A Phase II Neoadjuvant Study of Palbociclib in Combination with Letrozole and Trastuzumab as Neoadjuvant Treatment of Stage II-III ER+ HER2+ Breast Cancer (PALTAN)

Patients with ER+/HER2+ breast cancer are less likely to achieve pathological complete response (pCR) after neoadjuvant chemotherapy with dual HER2 blockade than patients with ER-/HER2+ breast cancer. Endocrine therapy plus trastuzumab is effective in advanced ER+/HER2+ breast cancer. Inhibition of CDK4/6 and HER2 results in synergistic reduction in cell proliferation in preclinical studies. We therefore combined palbociclib with letrozole and trastuzumab in ER+/HER2+ BC as a chemotherapy-sparing regimen.