This is an open-label study with multiple phases.
Eligible participants will receive neoadjuvant treatment with 12 administrations of weekly intravenous (IV) paclitaxel 80mg/m2 (or IV docetaxel 75mg/m2 every 3 weeks for 4 cycles), combined with subcutaneous injection (SC) fixed dose combination (FDC) of pertuzumab and trastuzumab (loading dose of 1200mg pertuzumab and 600mg trastuzumab, followed by 600mg pertuzumab and 60mg trastuzumab) every 3 weeks for 4 cycles.
Following this, all participants will undergo surgery, performed according to local guidelines.
After surgery, participants who achieve pathologic complete response (pCR, defined as pT0/Tis pN0) will receive adjuvant pertuzumab and trastuzumab FDC SC for an additional 14 cycles.
Participants with residual invasive disease will receive salvage adjuvant trastuzumab emtansine (T-DM1, 3.6 mg/kg, IV every 3 weeks) for 14 cycles.
In participants whose residual invasive disease is classified per Residual Cancer Burden (RCB) score as less than or equal to 2, 3 to 4 cycles of anthracycline-based chemotherapy may be administered, at the investigator's discretion, before the 14 cycles of T-DM1.