Researchers are looking for new ways to treat ovarian cancer (OC). Current treatment for OC may start with surgery to remove as much of the cancer as possible. After surgery, people may receive chemotherapy. After chemotherapy, standard care options may include:

* Maintenance treatment, which is used after another therapy to keep the cancer from growing, spreading, or coming back. Bevacizumab is a targeted therapy used as standard maintenance treatment. Targeted therapy works to control how specific types of cancer cells grow and spread.
* Observation, which is watching to see if cancer grows or worsens

The study medicine, sacituzumab tirumotecan (also called sac-TMT), is a targeted therapy. The goal of this study is to learn if people who receive sac-TMT maintenance treatment with or without bevacizumab live longer without the cancer getting worse than people who receive standard care.

Researchers are looking for new ways to treat types of breast cancer that are both:

* High-risk, which means the cancer may have a higher chance of getting worse or coming back after treatment
* Early-stage, which means the cancer is in the breast or the lymph nodes around the breast The 2 types of breast cancer in this study are triple-negative breast cancer (TNBC) and hormone receptor (HR)-low positive/human epidermal growth factor receptor-2 (HER2) negative breast cancer. These cancers have zero or a low amount of a protein called HER2 and other proteins that attach to the hormones estrogen or progesterone.

Sacituzumab tirumotecan (also known as sac-TMT or MK-2870), the study medicine, is a type of targeted therapy. A targeted therapy is a treatment that works to control how specific types of cancer cells grow and spread.

The main goals of this study are to learn if people who receive sac-TMT, pembrolizumab, and chemotherapy:

* Have fewer cancer cells found in the tumors and lymph nodes removed during surgery compared to those who receive only pembrolizumab and chemotherapy
* Live longer without the cancer growing, spreading, or coming back compared to people who receive only pembrolizumab with chemotherapy