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.