Abstract PO4-17-03: Neoadjuvant chemotherapy in invasive lobular carcinoma of the breast: A retrospective study on survival outcomes

Abstract Background: Neoadjuvant chemotherapy (NAC) is a well-established component of breast cancer management. Invasive lobular carcinoma (ILC) and invasive ductal carcinoma (IDC) are often treated similarly, but many studies are demonstrating a major difference in treatment responses according to the histopathological type of cancer. Aim: To evaluate the overall survival of patients with ILC after NAC compared with adjuvant chemotherapy. Methods: This retrospective cohort study included patients treated for breast ILC between 1998 and 2016 at the Center for Breast Diseases of de CHU de Québec – Université Laval, a tertiary breast cancer center. The primary outcomes were the overall survival (OS) and the recurrence-free survival (RFS) of ILC patients receiving NAC compared with patients who received only adjuvant chemotherapy. The follow-up was censored at the last hospital contact. The secondary outcomes were the locoregional recurrence, pathological complete response (pCR), and pCR impact on survival. Results: During the study period, 265 women were treated for ILC, of which 72 had NAC, and 193 had adjuvant therapy. No significant differences were observed regarding the patient’s characteristics (age, BMI, smoking, menopausal status, and use of hormonal replacement therapy). A T4 disease was found in 29.2% of the NAC group (vs. 0 in the adjuvant group), but the N2-3 rate was lower in the NAC group (5.6% vs. 22.3%, P=0.011). More patients in the NAC group underwent mastectomy (65.3% vs. 29.5%, P 0.0001) and axillary dissection (80.6% vs. 50.8%, P 0.0001). Three (4.2%) patients in the NAC group achieved a pCR. The rates of radiotherapy (P=0.851) and hormonal therapy (P=0.694) were similar between the two groups. The mean follow-up was 8 years. After adjustment for age, T, N, surgery type, radiotherapy, and hormonal therapy, the NAC group showed significantly lower 10-year OS (56.2% vs. 80.7%, P 0.0001) and RFS (51.8% vs. 72.7%, P=0.0004) compared with the adjuvant group. There were no differences in the 10-year local recurrence rate (90.6% vs. 93.5%, P=0.11). In a Cox regression analysis of RFS considering the previously mentioned covariables, more events in the NAC group (OR=2.52, 95%CI: 1.39-4.58, P=0.002) and patients with N2-N3 (OR=3.68, 95%IC: 2.00-6.80, P 0.01). Conclusion: Despite the general belief that ILC and IDC should be treated similarly, this study strongly suggests that ILC seems to have a poorer response to NAC. Patients diagnosed with ILC might benefit from a more aggressive surgical approach followed by adjuvant chemotherapy, no matter the severity of the disease. Additional long-term prospective comparative studies are needed to support this statement and improve the management of these patients. Citation Format: Virginie Gauthier, Anne-Julie Simard, Christine Desbiens, Brigitte Poirier, Julie Lemieux, Dominique Boudreau, Dominique Leblanc, Claudya Morin, Jean-Charles Hogue, Éric Poirier. Neoadjuvant chemotherapy in invasive lobular carcinoma of the breast: A retrospective study on survival outcomes abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-17-03.