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 study will evaluate the efficacy and safety of the combination of inavolisib plus a cyclin-dependent kinase 4 and 6 inhibitor (CDK4/6i) and letrozole versus placebo plus a CDK4/6i and letrozole in the first-line setting in participants with endocrine-sensitive PIK3CA-mutated hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-), advanced breast cancer (ABC).

This is a multicenter, Phase 1b/2 trial in participants with estrogen receptor positive/human epidermal growth factor receptor 2 negative (ER+/HER2-) advanced/metastatic breast cancer. The phase 1b part of the trial will determine the recommended Phase 2 dose (RP2D) of elacestrant when administered in combination with alpelisib, everolimus, palbociclib, capivasertib, and ribociclib. The Phase 2 part of the trial will evaluate the efficacy and safety of the various combinations.

The phase III trial compares the effect of pembrolizumab to observation for the treatment of patients with early-stage triple-negative breast cancer who achieved a pathologic complete response after preoperative chemotherapy in combination with pembrolizumab. Immunotherapy with monoclonal antibodies, such as pembrolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. This trial may help researchers determine if observation will result in the same risk of cancer coming back as pembrolizumab after surgery in triple-negative breast cancer patients who achieve pathologic complete response after preoperative chemotherapy with pembrolizumab.

This is an open-label, multicenter, two-arm Phase II clinical trial that will evaluate the impact of 2nd line chemotherapy (i.e. capecitabine) on survival in patients with non-Luminal A hormone receptor-positive (HR+) metastatic breast cancer (MBC)

The goal of this clinical trial is to evaluate the safety and efficacy of TOS-358 in women with HR+ HER2- metastatic breast cancer whose tumors have a mutation in PIK3CA and who meet all other study enrollment criteria. The main questions it aims to answer are:

1. Phase 1a: what is the maximum tolerated dose and recommended dose for phase 2?
2. Phase 1a: how safe and tolerable is TOS-358 at different dose levels when taken orally once or twice per day?
3. Phase 1b: how safe and effective is TOS-358 when given with standard of care medicines for HR+HER2- metastatic breast cancer (fulvestrant and CDK4/6i)

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.

The purpose of this study is to test the safety and effectiveness of the sequence of two investigational drugs (trastuzumab deruxtecan followed by datopotamab deruxtecan, or datopotamab deruxtecan followed by trastuzumab deruxtecan) to learn whether the treatment works in treating HER2-negative (HER2-low or HER2-0) metastatic breast cancer.

The names of the study drugs involved in this study are:

* Datopotamab deruxtecan (a type of antibody drug conjugate)
* Trastuzumab deruxtecan (a type of antibody drug conjugate)

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.

The purpose of this study is to determine if a combination of two drugs sacituzumab govitecan and atezolizumab works as a treatment for residual cancer in the breast or lymph nodes and have circulating tumor DNA in the blood.

This research study involves the following investigational drugs:

* Sacituzumab govitecan
* Atezolizumab