Hormonal therapy with fulvestrant 500 mg will be administered intramuscularly on days 1, 15 of the first cycle, and thereafter on day 1 of every 28-day cycle for up to 5 cycles before surgery. Docetaxel (T) 75 mg/m2 every 3 weeks will be given for four cycles. Trastuzumab (H, 8mg/kg for 1st cycle, then 6 mg/kg in subsequent cycles before and after surgery), pertuzumab (P, 840 mg for 1st cycle, then 420 mg in subsequent 3 cycles) will be given concurrently with docetaxel for a total of 4 cycles before surgery.

Hormonal therapy with fulvestrant 500 mg will be administered intramuscularly on days 1, 15 of the first cycle, and thereafter on day 1 of every 28-day cycle for up to 5 cycles before surgery.

To determine pathological complete remission rate at the time of surgery in ER-positive and HER2-positive breast cancer patients undergoing neoadjuvant chemoimmunotherapy (docetaxel, trastuzumab, pertuzumab) concurrently with neoadjuvant hormonal therapy with fulvestrant. Note: pCR, defined as the absence of invasive neoplastic cells of the primary tumor in the breast, remaining in-situ lesions are allowed, ypT0-is;

Partial pathological response rate at the time of surgery and biomarker changes in breast cancer (biopsy vs residual tumor) before and after neoadjuvant chemotherapy Note: pPR, defined as residual invasive disease of 1cm, ypT1a-b.

Hormonal therapy with fulvestrant 500 mg will be administered intramuscularly on days 1, 15 of the first cycle, and thereafter on day 1 of every 28-day cycle for up to 5 cycles before surgery. Docetaxel (T) 75 mg/m2 every 3 weeks will be given for four cycles. Trastuzumab (H, 8mg/kg for 1st cycle, then 6 mg/kg in subsequent cycles before and after surgery), pertuzumab (P, 840 mg for 1st cycle, then 420 mg in subsequent 3 cycles) will be given concurrently with docetaxel for a total of 4 cycles before surgery.

To determine pathological complete remission rate at the time of surgery in ER-positive and HER2-positive breast cancer patients undergoing neoadjuvant chemoimmunotherapy (docetaxel, trastuzumab, pertuzumab) concurrently with neoadjuvant hormonal therapy with fulvestrant. Note: pCR, defined as the absence of invasive neoplastic cells of the primary tumor in the breast, remaining in-situ lesions are allowed, ypT0-is;

Data not collected. The study has been terminated due to the PI no longer being employed at CTCA and not having rights to the trial information."After much effort, results were not able to be retained.

Hormonal therapy with fulvestrant 500 mg will be administered intramuscularly on days 1, 15 of the first cycle, and thereafter on day 1 of every 28-day cycle for up to 5 cycles before surgery. Docetaxel (T) 75 mg/m2 every 3 weeks will be given for four cycles. Trastuzumab (H, 8mg/kg for 1st cycle, then 6 mg/kg in subsequent cycles before and after surgery), pertuzumab (P, 840 mg for 1st cycle, then 420 mg in subsequent 3 cycles) will be given concurrently with docetaxel for a total of 4 cycles before surgery.