Ph2 Study for Optimization of Adjunct Systemic Therapy in HER2+ Patients, MolecularPCR Trial

PRIMARY OBJECTIVES: I. To determine the 3-year event free survival (EFS) after breast surgery in patients with early triple negative breast cancer (TNBC) that achieve a pathologic complete response (pCR) after neoadjuvant systemic therapy (NST) with a pembrolizumab plus chemotherapy-based regimen and are minimal residual disease (MRD)-negative (negative circulating tumor deoxyribonucleic acid \[ctDNA\] with the NeXT Personal™ assay) at 4-6 weeks after breast surgery and discontinue standard of care (SOC) adjuvant pembrolizumab. II. To determine the 3-year EFS after breast surgery in patients with early HER2+ breast cancer that achieve a pCR after NST with a trastuzumab and pertuzumab plus chemotherapy-based regimen and are MRD-negative (negative ctDNA with the NeXT Personal™ assay) at 4-6 weeks after breast surgery and discontinue SOC adjuvant trastuzumab and pertuzumab. SECONDARY OBJECTIVES: I. To estimate the rate of conversion from negative to positive ctDNA and time to conversion from negative to positive ctDNA among patients who undergo de-escalation of SOC adjuvant systemic therapy. II. To establish the prevalence of patients with early TNBC or early HER2+ breast cancer who achieve a pCR after receiving NST and have a positive ctDNA with the NeXT Personal™ assay at 4-6 weeks after breast surgery. III. To determine the 3-year EFS after breast surgery in patients with early HER2+ breast cancer or early TNBC that achieve a pCR after NST and have a positive ctDNA with the NeXT Personal™ assay at 4-6 weeks after breast surgery. OUTLINE: Patients with triple negative breast cancer are assigned to cohort 1, patients with HER2 positive breast cancer are assigned to cohort 2. COHORT 1: Patients may receive 1 to 3 cycles of standard of care treatment with pembrolizumab. Patients with a positive ctDNA test 4-6 weeks after surgery continue to receive standard of care treatment per their treating physician in the absence of disease progression or unacceptable toxicity. Patients with a negative ctDNA test will not receive further treatment with pembrolizumab and will undergo monitoring with ctDNA tests every 3 months for 3 years in the absence of disease progression. COHORT 2: Patients may receive 1 to 3 cycles of standard of care treatment with trastuzumab with or without pertuzumab. Patients with a positive ctDNA test 4-6 weeks after surgery continue to receive standard of care treatment per their treating physician in the absence of disease progression or unacceptable toxicity. Patients with a negative ctDNA test will not receive further treatment with pembrolizumab and will undergo monitoring with ctDNA tests every 3 months for 3 years in the absence of disease progression. Patients may receive standard of care endocrine therapy per their treating physician throughout the study.