Sacituzumab Govitecan With or Without Atezolizumab Immunotherapy in Rare Genitourinary Tumors (SMART) Such as High Grade Neuroendocrine Carcinomas, Adenocarcinoma, and Squamous Cell Bladder/Urinary Tract Cancer, Renal Medullary Carcinoma and Penile C...

Background: Rare tumors of the genitourinary (GU) tract can appear in the kidney, bladder, ureters, and penis. Rare tumors are difficult to study because there are not enough people to conduct large trials for new treatments. Two drugs-sacituzumab govitecan (SG) and atezolizumab-are each approved to treat other cancers. Researchers want to find out if the two drugs used together can help people with GU. Objective: To test SG, either alone or combined with atezolizumab, in people with rare GU tumors. Eligibility: Adults aged 18 years and older with rare GU tumors. These may include high grade neuroendocrine carcinomas; squamous cell carcinoma of the bladder; primary adenocarcinoma of the bladder; renal medullary carcinoma; or squamous cell carcinoma of the penis. Design: Participants will be screened. They will have a physical exam with blood and urine tests. They will have tests of heart function. They will have imaging scans. They may need a biopsy: A small needle will be used to remove a sample of tissue from the tumor. Both SG and atezolizumab are given through a tube attached to a needle inserted into a vein in the arm. All participants will receive SG on days 1 and 8 of each 21-day treatment cycle. Some participants will also receive atezolizumab on day 1 of each cycle. Blood and urine tests, imaging scans, and other exams will be repeated during study visits. Treatment may continue for up to 5 years. Follow-up visits will continue for 5 more years.