This research study is studying a combination of HER2-directed therapies (trastuzumab and pertuzumab) and hormonal therapy as a treatment after surgery for hormone receptor positive breast cancer.

The study drugs involved in this study are:

* A combination of trastuzumab and pertuzumab given as an injection under the skin (PHESGO)
* Hormonal (endocrine) Treatment

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.

The goal of this trial is to see if active surveillance monitoring and hormonal therapy in patients diagnosed with ductal cell carcinoma in situ (DCIS), an early stage of breast cancer, can be an effective management of the disease.

Participants will be asked to receive control hormonal therapy or an investigational hormonal therapy treatment. Participants will be asked to return for evaluation with MRI at three months and six months. Depending on the evaluation participants will have the option to continue on the treatment. If the evaluation suggests surgery is recommended, the participant will discontinue the study treatment and will undergo surgery. In addition to the treatment and MRI evaluation, participants will be asked to provide blood sample to understand their immune status, provide saliva sample for genetic testing, provide the study with a portion of the tissue or slides generated from tissue removed during surgery performed as part of their standard of care.

This is an umbrella study evaluating the efficacy and safety of multiple treatment combinations in participants with metastatic or inoperable locally advanced breast cancer.

The study will be performed in two stages. During Stage 1, four cohorts will be enrolled in parallel in this study:

Cohort 1 will consist of Programmed death-ligand 1 (PD-L1)-positive participants who have received no prior systemic therapy for metastatic or inoperable locally advanced triple-negative breast cancer (TNBC) (first-line \[1L\] PD-L1+ cohort).

Cohort 2 will consist of participants who had disease progression during or following 1L treatment with chemotherapy for metastatic or inoperable locally-advanced TNBC and have not received cancer immunotherapy (CIT) (second-line \[2L\] CIT-naive cohort).

Cohort 3 will consist of participants with locally-advanced or metastatic HR+, HER2-negative disease with PIK3CA mutation who may or may not have had disease progression during or following previous lines of treatment for metastatic disease (HR+cohort).

Cohort 4 will consist of participants with locally-advanced or metastatic HER2+ /HER2-low disease with PIK3CA mutation who had disease progression on standard-of-care therapies (HER2+ /HER2-low cohort).

In each cohort, eligible participants will initially be assigned to one of several treatment arms (Stage 1). In addition, participants in the 2L CIT-nave cohort who experience disease progression, loss of clinical benefit, or unacceptable toxicity during Stage 1 may be eligible to continue treatment with a different treatment combination (Stage 2), provided Stage 2 is open for enrollment.

This Phase III Trial evaluates whether breast conservation surgery and endocrine therapy results in a non-inferior rate of invasive or non-invasive ipsilateral breast tumor recurrence (IBTR) compared to breast conservation with breast radiation and endocrine therapy.

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)