Additional Study Information: The purpose of this study is to learn if the HBV medicine called tenofovir alafenamide can help reduce the chance that HBV gets worse or comes back during cancer treatment. It is not known if starting tenofovir alafenamide (TAF) with chemotherapy is better than waiting until HBV returns or becomes more active. Tenofovir alafenamide (TAF) is FDA approved and commercially available for the treatment of chronic HBV infection. There will be about 444 people taking part in this study. The purpose of this study is to compare taking tenofovir alafenamide when you start chemotherapy (study approach), versus taking tenofovir alafenamide if your chronic HBV becomes more active during your chemotherapy (usual approach). The study approach could prevent liver damage but might also cause side effects. This study will allow the researchers to know whether the study approach is better, the same, or worse than the usual approach. If better, the study approach should decrease liver damage in patients with HBV who undergo cancer treatment for cancer. Cancers include: bladder cancer, breast cancer, esophageal cancer, kidney cancer, adrenal cancer, lung cancer, sarcoma, thyroid cancer, gynecologic cancer, pancreatic cancer, stomach cancer, colorectal cancer, head and neck cancer, oral cancer, skin cancer, prostate cancer, and testicular cancer.