Low Total Pathologic Complete Response (tpCR) Rate to Preoperative Chemotherapy in Patients with Invasive Lobular Carcinoma of Breast (ILC): Analysis of Subgroup of Three Phase II Trials

Abstract

Background: Total pathologic complete response (tpCR; ypT0/is ypN0) after preoperative chemotherapy (PCT) is associated with better outcome in locally advanced breast cancers. However, the tpCR rate according to histology is not usually considered in trials. Patients and Methods: Patients with invasive lobular breast carcinoma (ILC), including in 3 phase II trials (AT, ATX and TXH), were eligible. Expression of markers and clinical phenotypes (CPh) were determined by immunohistochemistry. The primary end-point was tpCR rate in patients with ILC. Secondary end-points were breast conservation surgery rate (BCSR), event-free survival (EFS), and overall survival (OS). Results: In the subgroup of patients with ILC (n=16), median age was 50 years, 56.25% was premenopausal, median tumor size was 5 cm, and 68.75% had clinically node involvement. Six patients (37.5%) had clinical stage II and 10 (62.5%) had clinical stage III. Hormone receptor positive disease was present in 93.75% of the patients, and median Ki-67 was 25%. CPh were Luminal A-like in 37.5%, Luminal B-like in 50%, HER2-positive in 6.25% and triple negative in 6.25% of tumors. Only 1 patient (6.25%) had a tpCR, and another patient had a pCR only in the breast. With a median follow-up of 146 months, median EFS was 120 months (95% CI: 68-139), and median OS was not reached. Ten-year EFS and OS probability was 47% and 60%, respectively. BCSR