Abstract P3-11-05: Neoadjuvant chemotherapy in invasive lobular breast carcinoma: Comparison of response, surgery and disease free survival with invasive ductal carcinoma

Background Lobular breast cancer (ILC) has been reported to be associated with a lower rate of pathologic complete response (pCR) and breast conserving surgery following neoadjuvant chemotherapy compared with ductal carcinoma (IDC). ILC is predominantly oestrogen receptor positive, HER-2-ve and histologic grade 1 or 2. Oestrogen receptor positive breast cancer has been shown to have poorer responses to neoadjuvant chemotherapy. HER-2 positivity is associated with better responses to anthracycline based neoadjuvant chemotherapy than HER-2 negative, and substantially improved pathological complete response (pCR) rates relative to HER-2 negative disease with the use of HER-2 targeted agents in this patient group. This study investigates response and disease free survival of ILC compared with IDC. Methods Patients with ILC and IDC treated with neoadjuvant chemotherapy were identified from the prospectively collated breast unit database at the Royal Marsden Hospital. Demographic, tumour, treatment and outcome data was obtained from the database and hospital electronic patient record system. Statistical analysis was undertaken comparing IDC and ILC. Clinical response rates, pCR rates, breast conserving surgery rates, and disease free survival were analysed. Clinical response was defined as those with partial response (≥50% reduction in the product of breast tumour size from baseline measurement), or complete clinical response (no clinically palpable breast tumour). Subgroup analysis was performed on ER+ve, HER-2–ve and HER-2 unknown cases. Results A total of 1017 patients were identified. Of these, there were 920 IDC and 97 ILC cases. Median age at commencement of neoadjuvant chemotherapy was 47.9 years (range 23.6-74.9). Median follow-up was 7.6 years (range 0.2-26.5). Pathologic response rates were available for 717 patients. 119 (19%) IDC had pCR, and 1 (1.1%) ILC (p Within the ER+ve, HER2-ve/unknown group there were 403 IDC and 82 lobular patients. pCR results were available for 148 (30%) of the patients. 41 (15.8%) in the IDC and 1 (1.3%) in the ILC group had pCR (p=0.001). 335 (83.1%) in the IDC group and 64 (78.0%) in the ILC group had a clinical response (p 0.27). Breast conserving surgery rates were 212 (57.6%) in the ductal group and 30 (39.0%) in the lobular group (p 0.003). Conclusion Within the cohort entire rates of pCR and of breast conserving surgery were lower for those with ILC compared with IDC. Despite lower rates of pCR and breast conserving surgery in ILC, there was no difference in clinical response rates or in disease free survival compared with IDC. Significant differences in pCR and breast conserving surgery rates between ILC and IDC persisted on subgroup analysis of those with ER+ve HER2-ve/unknown breast cancer. Citation Format: Hilary L Martin, Geraldine Walsh, Komel Khabra, Tabitha Skinner, Ian E Smith. Neoadjuvant chemotherapy in invasive lobular breast carcinoma: Comparison of response, surgery and disease free survival with invasive ductal carcinoma [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-11-05.