Progression-free survival (PFS) is defined as the time from the date of randomization to the date of the first documented progression or death due to any cause. PFS will be assessed by the Blinded Independent Review Committee (BIRC) according to RECIST 1.1.

PFS was defined as the time from the date of randomization to the date of the first documented progression or death due to any cause. PFS was assessed via a local radiology assessment according to RECIST 1.1. If a patient did not have an event, PFS was censored at the date of last adequate tumor assessment. The PFS distribution was estimated using Kaplan-Meier methodology. Progression was defined as at least a 20% increase in the sum of diameter of all measured target lesions, taking as reference the smallest sum of diameter of all target lesions recorded at or after baseline. In addition to the relative increase of 20%, the sum must also demonstrate an absolute increase of at least 5 mm.

The primary outcome is the percentage change in Ki67 expression comparing pre-treatment to on-treatment specimens. Ki67 values were log-transformed for analysis, and results are summarized as the mean percentage change with 95% confidence intervals.

Percentage of participants who were alive without disease progression at 6-month follow-up based on local investigator assessment per RECIST v1.1 in Cohort A, Cohort B and Cohort C. Participants who progressed, died, or discontinued study before 6 months were counted as a failure.

Pathologic complete response (pCR) defined as absence of any residual invasive cancer on hematoxylin and eosin evaluation of the resected breast specimen and all sampled ipsilateral lymph nodes following completion of 24 weeks of treatment by local assessment (ypT0/Tis ypN0). Patients who experienced progression of disease while undergoing neoadjuvant therapy, or who did not receive surgery for any reason, or received antineoplastic treatment other than study drug(s) before surgery were considered as non-responders for the calculation of pCR rate.

Pathologic complete response (pCR) defined as absence of any residual invasive cancer on hematoxylin and eosin evaluation of the resected breast specimen and all sampled ipsilateral lymph nodes following completion of 24 weeks of treatment by local assessment (ypT0/Tis ypN0). Patients who experienced progression of disease while undergoing neoadjuvant therapy, or who did not receive surgery for any reason, or received antineoplastic treatment other than study drug(s) before surgery were considered as non-responders for the calculation of pCR rate.

Objective Response Rate (ORR) defined as the proportion of patients with a Best Overall Response (BOR) of Complete Response (CR) or Partial Response (PR) based on local investigator's assessment according to Response Evaluation Criteria In Solid Tumors Criteria (RECIST) 1.1. BOR was assessed per MRI or Ultrasound and defined as per RECIST 1.1 as CR for a disappearance of all non-nodal target lesions (TL)/non-target lesions (NTL) and a reduction in short axis to \< 10 mm of any pathological lymph nodes assigned as TL/NTL and no new lesion; as PR if not qualifying for CR but with a decrease from baseline ≥ 30% in the sum of diameter of all TL, no progression of NTL and no new lesion.

Objective Response Rate (ORR) defined as the proportion of patients with a Best Overall Response (BOR) of Complete Response (CR) or Partial Response (PR) based on local investigator's assessment according to Response Evaluation Criteria In Solid Tumors Criteria (RECIST) 1.1. BOR was assessed per MRI or Ultrasound and defined as per RECIST 1.1 as CR for a disappearance of all non-nodal target lesions (TL)/non-target lesions (NTL) and a reduction in short axis to \< 10 mm of any pathological lymph nodes assigned as TL/NTL and no new lesion; as PR if not qualifying for CR but with a decrease from baseline ≥ 30% in the sum of diameter of all TL, no progression of NTL and no new lesion.

Standard 3+3 dose escalation design (three dose levels of alpelisib plus sacituzumab govitecan) with dose-limiting toxicities (DLT) assessed during the first treatment cycle. If two or more of the six patients experienced a dose-limiting toxicity, dosing escalation would cease and maximum tolerated dose (MTD) would be reached. RP2D was the next lower dose at which \<1/6 subjects experienced a DLT.