Neoadjuvant Endocrine Therapy +/- the PI3K Inhibitor Inavolisib in HER2+, HR+, PIK3CA Mutant Early Breast Cancer

This is a multicenter, prospective, randomized, open-label, parallel-group, phase II study to evaluate the potential incremental efficacy and safety of inavolisib in the neoadjuvant treatment of early-stage HER2-positive, HR-positive, PIK3CA mutant breast cancer. 170 patients with confirmed eligibility criteria and PIK3CA mutant breast cancer will be randomized in a 1:1 ratio to receive: Neoadjuvant endocrine therapy in combination with dual anti-HER2 blockade consisting of ready-to-use fixed-dose combination of pertuzumab and trastuzumab as subcutaneous (PH-FDC SC) formulation q3w for 6 cycles (18 weeks) with (6cycles) or without inavolisib. Endocrine therapy consists of either tamoxifen 20mg or an aromatase inhibitor +/- GnRH analogue for premenopausal women and men. In both study arms, treatment will be given until surgery/core-biopsy, disease progression, unacceptable toxicity, or withdrawal of consent of the patient. All patients will undergo surgery or biopsy after completing study therapy to assess pCR rate.