Impact of neoadjuvant chemotherapy plus HER2-targeting on breast conservation rates: Surgical results from CALGB 40601 (Alliance).

501 Background: Neoadjuvant systemic therapy improves breast conserving therapy (BCT) rates, but the magnitude of this benefit is unknown in operable breast cancer. We sought to quantify this benefit in CALGB 40601, a phase III trial of paclitaxel (T) + HER2 blockade with either trastuzumab (TH), lapatinib (TL), or both (THL), by requiring the treating breast surgeon to determine BCT eligibility before and after neoadjuvant therapy and examining surgical results. Methods: Eligible patients (pts) had operable, newly diagnosed, noninflammatory stage II-III HER2+ breast cancer randomized to receive TH, TL or THL. Prior to, and again after neoadjuvant therapy, the treating breast surgeon determined whether the patient was a BCT candidate based on clinical and radiographic criteria, but the subsequent breast cancer operation was at the discretion of the surgeon and patient. Two endpoints examined were: (1) the conversion rate from BCT-ineligible to BCT-eligible and (2) the rate of successful BCT as determined ...