This is a randomized, open-label study comparing the efficacy and safety of adjuvant sacituzumab tirumotecan (MK-2870) in combination with pembrolizumab compared to treatment of physician's choice (TPC) in participants with triple-negative breast cancer (TNBC) who received neoadjuvant therapy and did not achieve a pathological complete response (pCR) at surgery. The primary objective is to compare sacituzumab tirumotecan plus pembrolizumab to TPC (pembrolizumab or pembrolizumab plus capecitabine) with respect to invasive disease-free survival (iDFS) per investigator assessment. It is hypothesized that sacituzumab tirumotecan plus pembrolizumab is superior to TPC with respect to iDFS per investigator assessment.

This is a Phase 1b open-label, 2-part study in 3 treatment groups. The 3 treatment groups are as follows:

Treatment Group 1: Palazestrant (OP-1250) in combination with ribociclib (KISQALI, Novartis Pharmaceuticals Corporation).

Treatment Group 2: Palazestrant (OP-1250) in combination with alpelisib (PIQRAY, Novartis Pharmaceuticals Corporation).

Treatment Group 3: Palazestrant (OP-1250) in combination with everolimus.

Treatment Group 4: Palazestrant (OP-1250) in combination with atirmociclib.

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

The primary goal of this study is to evaluate the effectiveness of elacestrant versus standard endocrine therapy in participants with node-positive, Estrogen Receptor-positive (ER+), Human Epidermal Growth Factor-2 negative (HER2-) early breast cancer with high risk of recurrence.

This research study is looking to see how well male breast cancer responds to preoperative treatment with endocrine therapy and which endocrine therapy regimen is the most effective treatment for male breast cancer.

The drugs used in this study are:

* Tamoxifen
* Anastrozole
* Degarelix
* Abemaciclib

This phase II trial studies how well TPIV100 and sargramostim work in treating patients with HER2 positive, stage II-III breast cancer that has residual disease after chemotherapy prior to surgery. It also studies why some HER2 positive breast cancer patients respond better to chemotherapy in combination with trastuzumab and pertuzumab. TPIV100 is a type of vaccine made from HER2 peptide that may help the body build an effective immune response to kill tumor cells that express HER2. Sargramostim increases the number of white blood cells in the body following chemotherapy for certain types of cancer and is used to alert the immune system. It is not yet known if TPIV100 and sargramostim will work better in treating patients with HER2 positive, stage II-III breast cancer.

This phase II ADC MATCH screening and multi-sub-study treatment trial is evaluating whether biomarker-directed treatment with one of three antibody-drug conjugates (ADCs) (sacituzumab govitecan, enfortumab vedotin, and trastuzumab deruxtecan) works in treating patients with solid tumor cancers that have high expression of the Trop-2, nectin-4, or HER2 proteins and that may have spread from where they first started (primary site) to nearby tissue, lymph nodes, or distant parts of the body (advanced) or to other places in the body (metastatic). Precision medicine is a form of medicine that uses information about a person's genes, proteins, and environment to prevent, diagnose, or treat disease in a way that is tailored to the patient. ADCs such as sacituzumab govitecan, enfortumab vedotin, and trastuzumab deruxtecan are monoclonal antibodies attached to biologically active drugs and are a form of targeted therapy. Sacituzumab govitecan is a monoclonal antibody, called sacituzumab, linked to a drug called govitecan. Sacituzumab attaches to a protein called Trop-2 on the surface of tumor cells and delivers govitecan to kill them. Enfortumab vedotin is a monoclonal antibody, enfortumab, linked to an anticancer drug called vedotin. It works by helping the immune system to slow or stop the growth of tumor cells. Enfortumab attaches to a protein called nectin-4 on tumor cells in a targeted way and delivers vedotin to kill them. Trastuzumab deruxtecan is composed of a monoclonal antibody, called trastuzumab, linked to a chemotherapy drug, called deruxtecan. Trastuzumab attaches to HER2 positive tumor cells in a targeted way and delivers deruxtecan to kill them. Personalized treatment with sacituzumab govitecan, enfortumab vedotin, or trastuzumab deruxtecan may be an effective treatment option for patients with advanced or metastatic solid tumors that screen positive for high expression of Trop-2, nectin-4, or HER2, respectively.

This open-label research study is studying (Z)-endoxifen as a possible treatment for pre-menopausal women with ER+/HER2- breast cancer. (Z)-endoxifen belongs to a group of drugs called selective estrogen receptor modulators or "SERM", which help block estrogen from attaching to cancer cells. This study has two parts: a pharmacokinetic part and a treatment part.

The PK part (how the body processes the drug) will enroll about 18 participants. All participants will take (Z)-endoxifen capsules daily. Twelve participants will be randomly assigned (50/50 chance) to take (Z)-endoxifen alone or (Z)-endoxifen with a monthly injection of goserelin a drug that temporarily stops the ovaries from making estrogen. This part will help determine the best dose of (Z)-endoxifen by measuring the drug levels in the blood and how long the body takes to remove it.

The Treatment Cohort has been simplified to a single study arm (Z)-endoxifen + goserelin. Up to 20 participants will be enrolled that have a baseline Ki-67 10% and 45 participants will be enrolled that have a baseline Ki-67\>10%.

A key goal of the study is to see if (Z)-endoxifen can slow down or stop tumor growth as measured by a reduction in Ki-67 levels. Tumor tissue samples will be taken by breast biopsy after about 4 weeks of treatment to check levels of this biomarker. If the tumor shows signs of response, participants can continue treatment for up to 24 weeks or until they have surgery.

Study participation is up to 6 months (24 weeks of treatment) followed by surgery and a one-month follow up visit.

This phase II trial tests how well evaluating circulating tumor deoxyribonucleic acid (ctDNA) works to guide therapy-change decisions in treating patients with triple-negative breast cancer (TNBC) that has spread from where it first started (primary site) to other places in the body (metastatic). This study wants to learn if small pieces of DNA associated with a tumor (called circulating tumor DNA, or ctDNA) can be detected in investigational blood tests during the course of standard chemotherapy treatment for breast cancer, and whether information from such investigational ctDNA blood testing could possibly be used as an early indication of chemotherapy treatment failure. It is hoped that additional information from investigational blood testing for ctDNA could help doctors to switch more quickly from a standard chemotherapy treatment that typically has significant side effects and which may not be working, to a different standard treatment regimen against TNBC, called sacituzumab govitecan. Sacituzumab govitecan is a monoclonal antibody, called hRS7, linked to a chemotherapy drug, called irinotecan. hRS7 is a form of targeted therapy because it attaches to specific molecules (receptors) on the surface of cancer cells, known as TROP2 receptors, and delivers irinotecan to kill them. Studying ctDNA may assist doctors to change therapy earlier if needed, and may improve health outcomes in patients with metastatic TNBC.

This ComboMATCH patient screening trial is the gateway to a coordinated set of clinical trials to study cancer treatment directed by genetic testing. Patients with solid tumors that have spread to nearby tissue or lymph nodes (locally advanced) or have spread to other places in the body (advanced) and have progressed on at least one line of standard systemic therapy or have no standard treatment that has been shown to prolong overall survival may be candidates for these trials. Genetic tests look at the unique genetic material (genes) of patients' tumor cells. Patients with some genetic changes or abnormalities (mutations) may benefit from treatment that targets that particular genetic mutation. ComboMATCH is designed to match patients to a treatment that may work to control their tumor and may help doctors plan better treatment for patients with locally advanced or advanced solid tumors.