• Subject is considered an adult according to local regulation at the time of signing the informed consent form (ICF).
• Subject has measurable disease by RECIST Version 1.1.
• Subject has accessible archival tumor tissue from either the primary tumor or a metastatic site, for which source and availability have been confirmed prior to study treatment. If no archival tumor tissue is available, the subject will have a biopsy to obtain tumor tissue prior to study treatment. If the subject is unable to undergo a biopsy due to safety concerns, enrollment into the study must be discussed with the medical monitor.
• For cohort 9 only: Subject should submit archival or fresh tumor tissue sample for programmed cell death-ligand 1 (PD-L1) central testing during screening if no local PD-L1 test result is available. Central test result for PD-L1 will be required prior to subject enrollment. For cohort 9 subjects with local PD-L1 test result confirming CPS ≥ 1, archival or fresh tissue sample for exploratory analysis should be submitted within 5 days of enrollment.
• Subject has ECOG performance status of 0 or 1.
• Subject has the following baseline laboratory data. If a subject has received a recent blood transfusion, the hematology tests must be obtained ≥ 28 days after any blood transfusion.
• absolute neutrophil count (ANC) ≥ 1.0 × 10^9/L
• platelet count ≥ 100 × 10^9/L
• hemoglobin ≥ 9 g/dL
• serum total bilirubin ≤ 1.5 × upper limit of normal (ULN) or ≤ 3 × ULN for subjects with Gilbert's disease
• creatinine clearance (CrCl) ≥ 30 mL/min as estimated per institutional standards or as measured by 24-hour urine collection (glomerular filtration rate [GFR] can also be used instead of CrCl).
• alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3 × ULN
• Subject agrees not to participate in another interventional study while receiving study treatment in the present study.
• Additional contraceptive requirements exist for male and female subjects. Disease Specific
• Evidence of progression on or after the last regimen received.
• Locally advanced or metastatic disease that is not amenable to curative intent treatment. Cohort 1: HR+/HER2- breast cancer
• Subject has evidence of radiographic progression on or after the last regimen received.
• Subject has histologically- or cytologically-confirmed HR+/HER2- (estrogen receptor [ER] positive and/or progesterone receptor [PR] positive, and HER2 negative) breast cancers and are not considered a candidate for further hormonal therapy. Subject will be considered HR+ if biopsies show ≥ 1% expression of ER or PR as per current American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) guidelines.
• Subject has locally advanced or metastatic disease that is not amenable to curative intent treatment.
• Subject must have received a taxane or anthracycline in the neoadjuvant, adjuvant or incurable, locally advanced or metastatic setting.
• Prior cytotoxic regimen received in the neoadjuvant or adjuvant setting will count as a prior cytotoxic regimen if disease recurrence occurred during or within 6 months of completing the regimen.
• Subject has progressed, relapsed, or discontinued for toxicity during or after at least 1 prior standard of care cytotoxic regimen in the incurable, unresectable locally advanced or metastatic setting, and has not received > 2 prior lines of cytotoxic therapy in the locally advanced or metastatic setting. No limit applies to endocrine therapies. Poly(ADP-ribose) polymerases (PARP) inhibitors do not count as a line of cytotoxic therapy.
• Subject has progressed, relapsed, or discontinued for toxicity during or after receiving endocrine therapy or with hormonally-directed therapy with cyclin-dependent kinase (CDK) inhibitors. Prior therapy with CDK inhibitors is not required. Cohort 2: triple negative breast cancer (TNBC)
• Subject has evidence of radiographic progression on or after the last regimen received.
• Subject has histologically- or cytologically-confirmed TNBC; defined as unequivocal TNBC histology (ER-negative/PR-negative/HER2-negative). This is defined by < 1% expression of ER and PR by immunohistochemistry (IHC), and that are, for HER2, either 0 to 1+ by IHC, or IHC 2+ and fluorescence in situ hybridization (FISH) negative (not amplified) as per current ASCO/CAP guidelines.
• Subject has locally advanced or metastatic disease that is not amenable to curative intent treatment.
• Subject must have received a taxane or anthracycline in the neoadjuvant, adjuvant or incurable, locally advanced or metastatic setting.
• Prior cytotoxic regimen received in the neoadjuvant or adjuvant setting will count as a prior cytotoxic regimen if disease recurrence occurred during or within 6 months of completing the regimen.
• Subject has progressed, relapsed, or discontinued for toxicity during or after at least 1 prior standard of care cytotoxic regimen in the incurable, unresectable locally advanced or metastatic setting, and has not received > 2 prior lines of cytotoxic therapy in the locally advanced or metastatic setting. Poly(ADP-ribose) polymerases (PARP) inhibitors do not count as a line of cytotoxic therapy.
• Subject has received prior therapy with an anti-programmed cell death protein-1 (PD-1) or an anti-programmed cell death-ligand 1 (PD-L1) based on subject's tumor PD-1 or PD-L1 expression and local treatment guidelines and has progressed or discontinued treatment due to toxicity, or therapy is contraindicated for subject. Cohort 3: squamous non-small cell lung cancer (NSCLC)
• Subject has evidence of radiographic progression on or after the last regimen received.
• Subject has histologically or cytologically-confirmed squamous NSCLC.
• Subjects with mixed histology NSCLC are eligible provided there is not any component of neuroendocrine histology.
• Subjects with known epidermal growth factor receptor (EGFR), anaplastic lymphoma kinase (ALK), reactive oxygen species (ROS), BRAF, or other actionable mutations are eligible if treated with mutation targeted therapy and have progressed, relapsed, or discontinued treatment due to toxicity.
• Subject has locally advanced or metastatic disease that is not amenable to curative intent treatment.
• Subject has progressed, relapsed, or discontinued treatment due to toxicity after 1 platinum-based standard of care regimen for locally advanced or metastatic disease, and has not received > 2 prior lines of cytotoxic anticancer therapy in the locally advanced or metastatic setting. 1. Subjects with locally advanced disease who previously received curative intent treatment with platinum-based standard of care regimen in the adjuvant or neoadjuvant setting or as part of concomitant chemoradiation therapy are eligible if they have progressed or relapsed within 6 months of completion. 2. Maintenance therapy does not constitute a new chemotherapy regimen provided there was no progression after the initial platinum-based regimen. 3. Changing chemotherapy agents during platinum-based treatment for the management of toxicities does not constitute a new chemotherapy regimen provided no progression had occurred while on the initial therapy.
• Subject has received prior therapy with an anti-PD-1 or anti-PD-L1 based on subject's tumor PD-1 or PD-L1 expression and local treatment guidelines and has progressed, relapsed, or discontinued treatment due to toxicity, or therapy is contraindicated for subject. Cohort 4: non-squamous non-small cell lung cancer
• Subject has evidence of radiographic progression on or after the last regimen received.
• Subject has histologically- or cytologically-confirmed non-squamous NSCLC.
• Subjects with mixed histology NSCLC are eligible provided there is not any component of neuroendocrine histology.
• Subjects with known EGFR, ALK, ROS, BRAF, or other actionable mutations are eligible if treated with mutation targeted therapy and have progressed, relapsed, or discontinued treatment due to toxicity.
• Subject has locally advanced or metastatic disease that is not amenable to curative intent treatment.
• Subject has progressed, relapsed, or discontinued treatment due to toxicity after 1 platinum-based standard of care regimen for locally advanced or metastatic disease, and has not received > 2 prior lines of cytotoxic anticancer therapy in the locally advanced or metastatic setting. 1. Subjects with locally advanced disease who previously received curative intent treatment with platinum-based standard of care regimen in the adjuvant or neoadjuvant setting or as part of concomitant chemoradiation therapy are eligible if they have progressed or relapsed within 6 months of completion. 2. Maintenance therapy does not constitute a new chemotherapy regimen provided there was no progression after the initial platinum-based regimen. 3. Changing chemotherapy agents during platinum-based treatment for the management of toxicities does not constitute a new chemotherapy regimen provided no progression has occurred while on the initial therapy.
• Subject has received prior therapy with an anti-PD-1 or anti-PD-L1 based on subject's tumor PD-1 or PD-L1 expression and local treatment guidelines and has progressed, relapsed, or discontinued treatment due to toxicity, or therapy is contraindicated for subject. Cohort 5: second-line or later head and neck cancer
• Subject has evidence of radiographic progression on or after the last regimen received.
• Subject has histologically- or cytologically-confirmed head and neck cancer.
• Primary tumor site must arise from the oral cavity, oropharynx, hypopharynx, and larynx; tumors arising from the nasopharynx are excluded. Salivary gland tumors and/or parotid gland tumors are not eligible for Cohort 5.
• Subject has locally advanced or metastatic disease that is not amenable to curative intent treatment.
• Subject has progressed, relapsed, or discontinued treatment due to toxicity after 1 platinum-based standard of care regimen for locally advanced or metastatic disease, and has not received > 2 prior lines of cytotoxic anticancer therapy in the locally advanced or metastatic setting.
• Subjects with locally advanced disease who previously received curative intent treatment with platinum-based standard of care regimen in the adjuvant or neoadjuvant setting or as part of concomitant chemoradiation therapy are eligible if they have progressed or relapsed within 6 months after completion.
• Subject has received prior therapy with an anti-PD-1 or anti-PD-L1 based on subject's tumor PD-1 or PD-L1 expression and local treatment guidelines and has progressed, relapsed, or discontinued treatment due to toxicity, or therapy is contraindicated for subject. Cohorts 6, 7 and 8: gastric or gastroesophageal junction (GEJ) or esophageal adenocarcinoma
• Subject has evidence of radiographic progression on or after the last regimen received.
• Subject has histologically- or cytologically-confirmed gastric, GEJ, or esophageal cancer.
• Subject has locally advanced or metastatic disease that is not amenable to curative intent treatment.
• Subject has progressed, relapsed, or discontinued due to toxicity after 1 platinum-based standard of care regimen for locally advanced or metastatic disease, and has not received > 2 prior lines of cytotoxic anticancer therapy in the locally advanced or metastatic setting.
• Neoadjuvant or adjuvant cytotoxic regimens will count as a prior regimen if relapsed or progressed ≤ 6 months after completion.
• Subject must have received a HER2 directed therapy if known to have HER2 positive cancer.
• Subject has received prior therapy with an anti-PD-1 or anti-PD-L1 based on subject's tumor PD-1 or PD-L1 expression and local treatment guidelines and has progressed, relapsed, or discontinued treatment due to toxicity, or therapy is contraindicated for subject. Cohort 9: 1L HNSCC
• Subject has histologically- or cytologically-confirmed head and neck squamous cell carcinoma. a. Primary tumor site must arise from the oral cavity, oropharynx, hypopharynx, and larynx; tumors arising from the nasopharynx are excluded. Salivary gland tumors and/or parotid gland tumors are not eligible for Cohort 9.
• Subject has recurrent or metastatic disease that is incurable by local therapies.
• Subject's tumor sample has PD-L1 combined positive score (CPS) of ≥ 1 as determined by local or central IHC testing.
• Subject has had no prior systemic therapy administered with the exception of systemic therapy completed > 6 months prior if given as part of multimodal treatment for locally advanced disease. Subjects who have received a PD-1 or PD-L1 inhibitor in the curative setting are eligible if it has been at least 12 months since last dose of the anti PD-L1 agent.
• Subject has ANC ≥ 1.5 × 10^9/L.
• International normalized ratio (INR) OR prothrombin time (PT) and activated partial thromboplastin (aPTT) both ≤ 1.5 × ULN unless subject is receiving anticoagulant therapy as long as PT or aPTT is within the therapeutic range of intended use of anticoagulants. PTT may be used if local lab is unable to perform aPTT.
• For subjects with oropharynx tumors, subject has results from testing of HPV status by p16 testing. For All Cohorts:
• Subject has preexisting sensory or motor neuropathy Grade ≥ 2.
• Subject has active central nervous system (CNS) metastases. Subjects with treated CNS metastases are permitted on study if all the following are true:
• CNS metastases have been clinically stable for ≥ 6 weeks prior to screening
• If requiring steroid treatment for CNS metastases, the subject is on a stable dose ≤ 20 mg/day of prednisone or equivalent for ≥ 2 weeks
• Baseline imaging scans show no evidence of new or enlarged brain metastasis
• Subject does not have leptomeningeal disease
• Subject has ongoing clinically significant toxicity (Grade 2 or higher with the exception of alopecia) associated with prior treatment (including systemic therapy, radiotherapy or surgery).
• Subjects with ongoing ≥ Grade 3 immunotherapy-related hypothyroidism or panhypopituitarism are excluded. Subjects with ongoing immunotherapy-related colitis, uveitis, myocarditis or pneumonitis, or subjects with other immunotherapy-related AEs requiring high doses of steroids (> 20 mg/day of prednisone or equivalent), are excluded. Subject with ≤ Grade 2 immunotherapy-related hypothyroidism or panhypopituitarism may be enrolled when well maintained/controlled on a stable dose of hormone replacement therapy (if indicated).
• Subject has a history of uncontrolled diabetes mellitus within 3 months before the first dose of study treatment. Uncontrolled diabetes (within 3 months before first dose) is defined as hemoglobin A1c (HbA1c) ≥ 8% or HbA1c between 7 and < 8% with associated diabetes symptoms (polyuria or polydipsia) that are not otherwise explained. The lowest HbA1c during the screening period will be used to determine eligibility.
• Subject has prior treatment with enfortumab vedotin or other monomethyl auristatin E (MMAE) based antibody-drug conjugates (ADCs).
• Subject has a second malignancy diagnosed within 3 years before first dose of study drug, or any evidence of residual disease from a previously diagnosed malignancy. Subjects with non-melanoma skin cancer, localized prostate cancer treated with curative intent with no evidence of progression, low-risk or very low-risk (per standard guidelines) localized prostate cancer under active surveillance/watchful waiting without intent to treat, or carcinoma in situ of any type (if complete resection was performed) are allowed.
• Subject is currently receiving systemic antimicrobial treatment for viral, bacterial, or fungal infection at the time of first dose of study treatment. Routine antimicrobial prophylaxis is permitted.
• Subject has known active hepatitis B (e.g., hepatitis B surface antigen [HBsAg] reactive) or active hepatitis C (e.g., hepatitis C virus [HCV] RNA [qualitative] is detected).
• Subject has known history of human immunodeficiency virus (HIV) infection (HIV 1 or 2).
• Subject has documented history of a cerebral vascular event (stroke or transient ischemic attack), unstable angina, myocardial infarction or cardiac symptoms (including congestive heart failure) consistent with New York Heart Association Class III-IV within 6 months prior to the first dose of study drug.
• Subject has major surgery within 4 weeks prior to first dose of study drug.
• Subject had radiotherapy, chemotherapy, biologics, investigational agents, and/or antitumor treatment with immunotherapy that is not completed 2 weeks prior to first dose of study drug.
• Subject has known hypersensitivity to enfortumab vedotin or to any excipient contained in the drug formulation of enfortumab vedotin (including histidine, trehalose dihydrate and polysorbate 20) OR subject has known hypersensitivity to biopharmaceutical produced in Chinese hamster ovary cells.
• Subject has known active keratitis or corneal ulcerations. Subject with superficial punctate keratitis is allowed if the disorder is being adequately treated.
• Subject has any condition which makes the subject unsuitable for study participation. Cohort 9: 1L HNSCC
• Had PD within 6 months of completion of curatively intended systemic treatment for locoregionally advanced HNSCC.
• Has had an allogeneic tissue/solid organ transplant. Has severe hypersensitivity (≥grade 3) to pembrolizumab and/or any of its excipients.
• Has a history of (non-infectious) pneumonitis / interstitial lung disease that required steroids or has current pneumonitis / interstitial lung disease.
• Has a history of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, idiopathic pneumonitis, or evidence of active pneumonitis on screening chest CT scan.
• Has a life expectancy of less than 3 months and/or has rapidly progressing disease (e.g. tumor bleeding, uncontrolled tumor pain) in the opinion of the treating investigator.
• Active autoimmune disease that has required systemic treatment in past 2 years (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive drugs). 1. Replacement therapy (e.g., thyroxine, insulin, physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency) is not considered a form of systemic treatment and is allowed. 2. Brief (<7 days) use of systemic corticosteroids is allowed when use is considered standard of care. 3. Subjects with vitiligo, psoriasis, type 1 diabetes mellitus, hypothyroidism, or resolved childhood asthma/atopy will not be excluded. 4. Subjects requiring intermittent use of bronchodilators, inhaled steroids, or local steroid injections will not be excluded. 5. Subjects with hypothyroidism that is stable with hormone replacement or Sjögren's syndrome will not be excluded.
• Has an active infection requiring systemic therapy.
• Has received prior therapy with an anti-PD-1 or anti-PD-L1 agent in the recurrent/metastatic setting. If anti-PD-1 or anti-PD-L1 agent was given as part of curative intent therapy, it must be at least 1 year since last dose.
• Has received a live vaccine within 30 days of planned start of study therapy. Examples of live vaccines include, but are not limited to, the following: measles, mumps, rubella, varicella/zoster (chicken pox), yellow fever, rabies, Bacillus Calmette Guérin, and typhoid vaccine. Seasonal influenza vaccines for injection are generally killed virus vaccines and are allowed; however, intranasal influenza vaccines (e.g., FluMist®) are live attenuated vaccines and are not allowed.
• Subject has active tuberculosis

• Subjects with advanced or metastatic solid tumor in subjects whose disease has progressed despite standard therapy, or who has no further standard therapy, or who is unsuitable for available standard treatment options.
• Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1 with adequate organ function
• Have known PD-L1 status with prior testing by immunohistochemistry and a corresponding combined positive score (CPS) For dose expansion study only:
• Advanced or metastatic gastric cancer, gastroesophageal junction carcinoma, and esophageal adenocarcinoma without further standard therapy or unsuitable for available standard treatment options.
• Must have CLDN18.2-positive tumor expression as determined by the CLDN18.2 IHC assay Exclusion Criteria
• Prior exposure to CLDN18.2 -targeted therapy
• Prior exposure to 4-1BB agonists
• Second malignancy within the last 3 years with the exception of cutaneous squamous cell carcinoma or cutaneous basal cell carcinoma or cervical carcinoma in situ
• Known active or chronic Hepatitis B or Hepatitis C, other hepatitides
• Unstable/active ulcer or digestive tract bleeding within 6 weeks
• Active autoimmune disease requiring systemic treatment within the past 2 years
• Active interstitial lung disease (ILD) or pneumonitis or a history of ILD or pneumonitis requiring treatment
• Known active CNS metastases and/or carcinomatous meningitis. Subjects with previously treated brain metastases may participate provided they are clinically stable and without requirement of steroid treatment for at least 14 days prior to first dose of study treatment;
• New York Heart Association (NYHA) Class 3 or 4 congestive heart failure, severe/unstable angina, myocardial infarction (MI), symptomatic congestive heart failure, cerebrovascular accident, transient ischemic attack (TIA), arterial embolism, pulmonary embolism, percutaneous transluminal coronary angioplasty (PTCA), deep vein thrombosis, or coronary artery bypass grafting (CABG) in the previous 6 months
• Diagnosis of immunodeficiency such as known active HIV
• Any active infection requiring parenteral treatment

• STEP 0 INCLUSION CRITERIA
• Histologically proven mucosal melanoma by local pathology
• Central PD-L1 tumor tissue submission
• STEP 1 INCLUSION CRITERIA
• Receipt of the central PD-L1 testing results available
• Disease status-Resected R0 or R1 disease patients. Patients eligible for randomization have resected R0 or R1 disease (with negative margins or positive microscopic margins) that must meet one of the following 4 criteria as defined below:
• Regional lymph node (LN) involvement; OR
• In-transit metastases/satellite primary disease; OR
• Single localized, primary disease meeting one of the following site-specific requirements:
• Head/neck
•Sinonasal (including nasopharynx): any primary lesion; Nasal or oral cavity; pT4a or above, given slightly improved OS
• NOTE: Conjunctival: does not meet the qualification for eligibility
• Anorectal
•any primary lesion
• Vaginal/cervical
•any primary, as they have 5 year OS rates of 5-25
• Urinary tract
•any primary urethral or bladder tumor
• Penile
• Vulvar- AJCC cutaneous stage IIB or higher
• Esophageal/gallbladder
•any primary
• Locoregionally recurrent following prior resection, meeting at least one of the above criteria
• In addition, patients must have undergone cross-sectional imaging of the brain, chest, abdomen and pelvis with no evidence of distant metastatic disease
• Disease status-Non-resected R2 or metastatic disease patients
• Non-resected R2 or metastatic disease that is assessable and measurable radiographically or by physical examination
• Prior Treatment:
• No prior systemic checkpoint inhibitor therapy of mucosal melanoma, including in the adjuvant setting, is allowed. Prior adjuvant chemotherapy or interferon is allowed.
• No other active, concurrent malignancy that requires ongoing systemic treatment or interferes with radiographic assessment of melanoma response as determined by the investigator. Exceptions may allow for adjuvant no evidence of disease (NED) cancers undergoing hormone based therapy may be eligible pending the other eligibility criteria are met and the principal investigator (PI) affirms the hormonal agent would not change the melanoma response.
• Any radiation must have completed 28 days prior to randomization and the patient must have adequately recovered from its effects.
• For resectable patients only: Surgery must have completed 28 days prior to randomization.
• For resectable patients only: Surgery must have completed no more than 84 days prior to randomization.
• Not pregnant and not nursing, because this study has an agent that has known genotoxic, mutagenic and teratogenic effects. Therefore, for women of childbearing potential only, a negative pregnancy test done =< 7 days prior to registration is required
• Age >= 18 years
• Eastern Cooperative Oncology Group (ECOG) performance status 0-2
• Absolute neutrophil count (ANC) >= 1,500/mm^3
• Platelet count >= 100,000/mm^3
• Creatinine =< 1.5 x upper limit of normal (ULN) OR creatinine clearance (CrCl) >= 50mL/min/1.73 m^2 for patients with creatinine levels above institutional normal
• Albumin >= 2.8 g/dL
• Total bilirubin =< 1.5 x upper limit of normal (ULN)
• Aspartate aminotransferase (AST)/alanine aminotransferase (ALT) =< 2.5 x upper limit of normal (ULN)
• No cardiovascular disease, including:
• No history of acute coronary syndromes (including myocardial infarction and unstable angina), coronary artery bypass graft (CABG) coronary angioplasty, or stenting within 6 months prior to study entry.
• No history of current class II or higher congestive heart failure as defined by the New York Heart Association (NYHA) functional classification system.
• No refractory hypertension defined as a blood pressure of systolic > 140 mmHg and/or diastolic > 90 mmHg despite adequate attempts at anti-hypertensive therapy.
• No history of myocarditis.
• No history of syncope of cardiovascular etiology, uncontrolled cardiac arrhythmia, history of Mobitz II second degree or third degree heart block without a permanent pacemaker in Association (NYHA) class II to IV heart failure, or stroke/transient ischemic attack (TIA) within the past 3 months.
• No corrected QT interval by Fridericia's formula (QTcF) > 500 msec. Note: if initial QTcF is found to be > 500 ms, two additional EKGs separated by at least 3 minutes should be performed. If the average of these three consecutive results for QTcF is =< 500 ms, the subject meets eligibility in this regard.
• No underlying hematologic issues, including:
• Congenital bleeding diathesis
• Gastrointestinal (GI) bleeding requiring intervention within the past 6 months, unless directly related to mucosal melanoma
• Active hemoptysis within 42 days prior to study enrollment.
• Active tumor lesions with cavitations or tumor lesions which invade, encase, or abut major blood vessels. The anatomic location and characteristics of primary tumors or metastases as well as the medical history should be carefully reviewed in the selection of subjects for treatment with cabozantinib/placebo.
• Pulmonary emboli or deep vein thromboses (DVT) that require an active anticoagulation regimen.
• No known or suspected history of cytopenia (low white blood cell [WBC], hemoglobin or platelet count) of greater than 3 months duration with an unknown cause, myelodysplastic syndrome, or hematologic malignancies.
• No clinical, laboratory or radiographic evidence of an active bacterial, fungal, or viral infection requiring treatment at the time of pre-registration (e.g., active symptoms of COVID-19 infection or a post-infectious symptomatic autoimmune syndrome, serious bacterial infections requiring antibiotics).
• No known or suspected gastrointestinal disorder affecting absorption of oral medications.
• Comorbid conditions:
• No active autoimmune disease or any condition requiring systemic treatment with either corticosteroids (> 10 mg daily of prednisone equivalents) or other immunosuppressive medications within 14 days of study drug administration. Inhaled or topical steroids and adrenal replacement doses > 10 mg daily prednisone equivalents are permitted in the absence of active autoimmune disease.
• No history of autoimmune motor neuropathy (e.g., Guillain-Barre syndrome, myasthenia gravis) or non-infectious pneumonitis.
• No history of severe allergic reactions to an unknown allergen or any components of the study drugs or its excipients.
• No history of gastrointestinal perforation or abdominal fistula.
• No clinically suspected central nervous system (CNS) (leptomeningeal or parenchymal) metastases. Patients with a history of CNS metastasis(s) will be allowed as long as
• The metastatic site(s) were adequately treated as demonstrated by clinical and radiographic improvement, AND
• The patient has recovered from the intervention (no residual adverse events > Common Terminology Criteria for Adverse Events [CTCAE] grade 1), AND
• The patient has remained without occurrence of new or worsening CNS symptoms for a period of 28 days prior to enrollment.
• No history of seizure or any condition that may increase the patient's seizure risk (e.g., prior cortical stroke, significant brain trauma) within 2 years.
• No clinically active or chronic liver disease resulting in moderate/severe hepatic impairment (Child-Pugh class B or C), ascites, coagulopathy or bleeding due to liver dysfunction.
• No untreated spinal cord compression or evidence of spinal metastases with a risk of impending fracture or spinal cord compression. Spinal metastases must have completed planned radiation or surgical therapy prior to registration.
• Concomitant medications:
• Chronic concomitant treatment with strong inhibitors of CYP3A4 is not allowed on this study. Patients on strong CYP3A4 inhibitors must discontinue the drug for 5 days prior to the start of study treatment.
• Chronic concomitant treatment with strong CYP3A4 inducers is not allowed. Patients must discontinue the drug 5 days prior to the start of study treatment.

• Participants with a cancer diagnosis: Documentation of disease:
• Histologic documentation: Histologically confirmed diagnosis of invasive cancer
• Stage: Stage I-IV per American Joint Committee on Cancer (AJCC) 7th edition, with the exception of patients with leukemia, lymphoma, and multiple myeloma
• For leukemia: Type (chronic lymphocytic leukemia [CLL], chronic myeloid leukemia [CML], acute lymphoblastic lymphoma [ALL], acute myeloid leukemia [AML])
• For lymphoma: Stage I-IV based on Ann Arbor staging
• For multiple myeloma: Stage I, II, III based on Revised International Staging System (RISS)
• One of the following tumor types:
• Colorectal
• Bladder
• Head and neck
• Hepatobiliary
• Lung
• Lymphoma
• Leukemia
• Ovary *** For these specific cancer types only, patients may be enrolled prior to histologic confirmation of malignancy. Sites are required to contact the study chairs to review appropriateness for enrollment
• Pancreas *** For these specific cancer types only, patients may be enrolled prior to histologic confirmation of malignancy. Sites are required to contact the study chairs to review appropriateness for enrollment
• Multiple myeloma
• Gastric, esophageal or gastroesophageal
• Breast
• Thyroid
• Kidney
• For these specific cancer types only, patients may be enrolled prior to histologic confirmation of malignancy. Sites are required to contact the study chairs to review appropriateness for enrollment
• Endometrium
• Prostate
• Melanoma *** For these specific cancer types only, patients may be enrolled prior to histologic confirmation of malignancy. Sites are required to contact the study chairs to review appropriateness for enrollment
• Sarcoma
• Participants with a cancer diagnosis: No prior definitive systemic or local anti-cancer intervention
• Participants with a cancer diagnosis: Age >= 40 and =< 75
• Participants with a cancer diagnosis: No known current pregnancy by self-report
• Participants with a cancer diagnosis: No known or prior history of in situ or invasive malignancy (excluding in situ non-melanoma skin cancers) other than the current cancer diagnosis
• Participants with a cancer diagnosis: Willingness to provide blood samples for research use
• Participants with a cancer diagnosis: Absence of medical contraindications to a research blood draw volume of 60 mL
• Participants with a cancer diagnosis: No history of organ transplantation
• Participants with a cancer diagnosis: Ability to read and comprehend English or Spanish * Eligibility is restricted to individuals who can comprehend and read English or Spanish given that participation in the study will require the ability to read and complete questionnaires that are available only in those two languages
• Participants without a cancer diagnosis and without suspicion of cancer: Age >= 40 and =< 75
• Participants without a cancer diagnosis and without suspicion of cancer: No known current pregnancy by self-report
• Participants without a cancer diagnosis and without suspicion of cancer: No known or prior history of in situ or invasive malignancy (excluding in situ non-melanoma skin cancers)
• Participants without a cancer diagnosis and without suspicion of cancer: Willingness to provide blood samples for research use
• Participants without a cancer diagnosis and without suspicion of cancer: Absence of medical contraindications to a research blood draw volume of 60 mL
• Participants without a cancer diagnosis and without suspicion of cancer: No history of organ transplantation
• Participants without a cancer diagnosis and without suspicion of cancer: Ability to read and comprehend English or Spanish * Eligibility is restricted to individuals who can comprehend and read English or Spanish given that participation in the study will require the ability to read and complete questionnaires that are available only in those two languages
• Participants with a high suspicion of cancer: High suspicion of ovarian cancer, pancreatic cancer, kidney cancer, or melanoma by clinical and/or radiological assessment, with plans for histologic or cytologic confirmation within 28 days after study blood draw * Examples of highly suspicious cases include: elevated CA125 and abnormal transvaginal ultrasound, suspicious renal or pancreatic mass on imaging, suspicious cutaneous lesion concerning for melanoma
• Participants with a high suspicion of cancer: Central review of radiology reports and/or clinical documentation conducted by study chairs
• Participants with a high suspicion of cancer: Age >= 40 and =< 75
• Participants with a high suspicion of cancer: No known current pregnancy by self-report
• Participants with a high suspicion of cancer: No known or prior history of in situ or invasive malignancy (excluding in situ non-melanoma skin cancers) other than the current cancer diagnosis
• Participants with a high suspicion of cancer: Willingness to provide blood samples for research use
• Participants with a high suspicion of cancer: Absence of medical contraindications to a research blood draw volume of 60 mL
• Participants with a high suspicion of cancer: No history or organ transplantation
• Participants with a high suspicion of cancer: Ability to read and comprehend English or Spanish * Eligibility is restricted to individuals who can comprehend and read English and Spanish given that participation in the study will require the ability to read and complete questionnaires that are available only in those two languages

Key
• Availability of tumor tissue (archived and fresh tumor biopsy, if medically feasible)
• Select advanced or metastatic solid tumor that is likely to express CLDN18.2 such as gastric/GEJ, pancreatic and esophageal cancer
• ≥ 18 years of age
• ECOG performance status (PS) 0 or 1 at Screening
• Progressed on or after standard therapy, or are intolerable for available standard therapy, or there is no available standard therapy
• Have at least one measurable extra-cranial lesion as defined by RECIST v1.1
• Adequate organ function
• Life expectancy > 12 weeks
• Ability to understand the nature of this study, comply with protocol requirements, and give written informed consent
• Willingness of men and women of reproductive potential to observe conventional and effective birth control for the duration of treatment and for 3 months following study completion Key
• Pregnant or breastfeeding
• Symptomatic or untreated brain metastases
• Have previously received CLDN18.2 antibody drug conjugates (ADCs) or any ADC containing an auristatin payload (prior monoclonal antibody against CLDN18.2 may be eligible)
• Have peripheral neuropathy Grade ≥2
• Have history of non-infectious pneumonitis/interstitial lung disease
• Have diagnosis of another malignancy, or history of systemic treatment for invasive cancer within last 3 years. Note: Patients with Stage I cancer who have received definitive local treatment and are considered unlikely to recur are eligible. Diagnosis of non-melanoma skin cancer, carcinoma in situ of the cervix or breast, or noninvasive tumor does not affect eligibility
• Have active ocular surface disease at baseline (based on screening ophthalmic examination)
• Have serious concurrent illness or clinically relevant active bacterial, fungal or viral infection
• Have previous hypersensitivity to any known components of EO-3021 or history of severe infusion reaction or hypersensitivity (CTCAE Grade 3 or higher) with monoclonal antibody treatment
• Clinically significant cardiac disease, including but not limited to symptomatic congestive heart failure, unstable angina, acute myocardial infarction within 6 months of planned first dose, or unstable cardiac arrhythmia requiring therapy (including torsades de pointes)
• Have history of allogenic hematopoietic stem cell transplantation or solid organ transplantation with ongoing systemic immunosuppressive therapy
• Patients who are not appropriate candidates for participation in this clinical study for any other reason as deemed by the Investigator