Low total pathologic complete response rate to preoperative chemotherapy in patients with invasive lobular carcinoma of the breast

Introduction
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.

Material and methods
Patients with invasive lobular breast carcinoma (ILC), who were included in three phase II trials (AT, ATX, and TXH), were eligible. Expression of markers and clinical phenotypes (CPh) were determined by immunohistochemistry. The primary endpoint was tpCR rate in patients with ILC. Secondary endpoints were breast-conserving surgery rate (BCSR), event-free survival (EFS), and overall survival (OS).

Results
In the subgroup of patients with ILC (n = 16) the median age was 50 years, 56.25% were premenopausal, median tumour 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 tumours. Only one patient (6.25%) had a tpCR, and another patient had a pathologic complete response (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 were 47% and 60%, respectively. BCSR was only 12.5%.

Conclusions
PCT in patients with ILC is associated with low tpCR rate because the majority of these patients have Luminal tumours with low chemo-sensitivity.