You can participate in this study if you:

1. Male or female equal or greater than 18 years of age and willing and able to provide informed consent.
2. Histologically or cytologically confirmed malignancy other than de novo (i.e., non-transformed) Small Cell Lung Cancer (SCLC) or (neuroendocrine prostate cancer) NEPC. Must be stage IV (metastatic); participants with stage III disease are eligible provided that they are not candidates for surgery and/or radiotherapy with curative intent.
3. Positive DLL3 expression by immunohistochemistry on tumor biopsy.
4. Participants must have progressed on or following at least one line of therapy, if a standard of care therapy exists for the tumor type.
5. Measurable disease, as per RECIST 1.1
6. ECOG performance status of 0-1

You cannot participate in this study if you:

1. Diagnosis of SCLC (with the exception of SCLC transformed from previously-treated Non-Small Cell Lung Cancer (NSCLC)) or NEPC.
2. Tumor specimen is not evaluable for DLL3 expression or tumor has DLL3 surface expression less than 1 percent by immunohistochemistry.
3. Progressive or symptomatic brain metastases. Brain metastases that have been radiated, are asymptomatic, and on a stable or decreasing dose of steroids are allowed. Leptomeningeal disease is excluded.
4. Evidence of interstitial lung disease or active, non-infectious pneumonitis. Exception: pneumonitis related to prior radiation therapy that is grade 1 and stable or improving without treatment.
5. Concurrent enrollment in another clinical study, unless enrolled only in the follow-up period or an observational study. Use of any investigational anticancer therapy must not have been received within 28 days prior to the first dose of study drugs.
6. Any chemotherapy, antibody drug conjugate or immunotherapy for cancer treatment in the prior 21 days, or small molecular inhibitor in the prior 7 days.
7. Prior therapy with any selective inhibitor of the DLL3 pathway.
8. Prior history of severe or life-threatening events from any immune-mediated therapy.
9. Receiving systemic corticosteroid therapy or any other form of immunosuppressive therapy within 7 days prior to enrollment. Low-dose corticosteroids (prednisone less than or equal to 10 mg per day or equivalent is permitted)
10. Major surgical procedures within 28 days prior to first dose of study treatment.
11. Treatment with live virus, including live-attenuated vaccination, within 14 days prior to the first dose of study treatment. Inactive vaccines (e.g., non-live or non-replicating agent) and live viral non-replicating vaccines within 3 days prior to first dose of study treatment.
12. History of myocardial infarction and/or symptomatic congestive heart failure (New York Heart Association, class II) within 6 months prior to first dose of study treatment.
13. History of arterial thrombosis (e.g., stroke or transient ischemic attack) within 6 months prior to first dose of study treatment.
14. Human immunodeficiency virus (HIV) infection.
15. Active hepatitis C infection.
16. Active hepatitis B infection.
17. Participants with symptoms and/or clinical signs and/or radiographic signs that indicate an acute and/or uncontrolled active systemic infection within 7 days prior to the first dose of study treatment.
18. Female participants of childbearing potential unwilling to use protocol specified method of contraception during treatment and for an additional 60 days after the last dose of study treatment.
19. Female participants who are breastfeeding or who plan to breastfeed.