Clinical Impact and Outcomes of Neoadjuvant Systemic Therapy for Invasive Lobular Carcinoma

Background Studies regarding therapeutic response of invasive lobular carcinoma (ILC) to neoadjuvant systemic therapy (NST) suggest that ILC is less favorable and the prognostic impact of a pathologic complete response (pCR) is unclear. Patients and Methods This study included 853 (NAC; n = 715 and NET; n = 138) non-metastatic classic ILC cases that received NST followed by surgery. Propensity-score matched analysis (PSMA) was performed to compare clinicopathologic groups. Survival outcomes were compared for patients with and without a pCR. Results Most had large primary tumors with nodal metastases (89.5% cT2–T4, 64% cN+) and luminal subtype tumors (87.6%). Patients receiving NAC were more likely to be clinically node-positive (69.1% versus 34.3%; p = 0.0005), have grade 3 disease (18.7% versus 8.7%; p = 0.0082), and undergo mastectomy (84.2% versus 69.6%; p < 0.001) and ALND (84.9% versus 57.3%; p < 0.0001) compared with NET. Overall, breast and axillary nodal pCR rates were 4.9% and 9.3%, respectively. Among 155 patients who had SLNB, there was 1 axillary nodal recurrence (0.6%). The 10-year distant recurrence-free survival (DRFS) for patients with a breast pCR was 61% versus 46% for those without ( p = 0.267). Patients with a nodal pCR demonstrated higher 10-year DRFS (49% versus 33%; p = 0.026) and OS compared with those without (65% versus 48%; p = 0.068). No survival outcome difference was seen for patients treated with NAC versus NET on PSMA. Conclusions Nodal pCR was associated with survival outcomes in ILC and systemic therapy decision-making should be reconsidered. SLNB after NST appears to be safe and effective in ILC.