255PPrognosis of selected triple negative apocrine breast cancer patients who did not receive adjuvant chemotherapy

Abstract Background Triple negative breast cancers are a heterogeneous group of breast cancer candidate to adjuvant chemotherapy in a large majority of cases. However, literature data indicate that the diagnosis of special types of breast cancer might be associated with a different outcome if compared with invasive ductal carcinoma with similar biological features and stages. Selected triple negative apocrine breast cancer can have an extremely good prognosis. Methods Among the 210 women with first primary invasive apocrine non metastatic breast cancer operated between January 1998 and December 2016 at European Institute Oncology, Milan, we identified 24 patients with pT1-pT2, node-negative, triple negative subtype and Ki-67 ≤20% who did not receive adjuvant chemotherapy. We compared the outcome of this cohort with a similar group of 48 patients with ductal tumors who received adjuvant chemotherapy, matched by pathological stage and biological features (matching ratio 1:2). Results The median age was 63 and 50 years in the apocrine and ductal group, respectively. The mean value of Ki-67 expression was 12% in the apocrine group and 14% in the ductal group. 83% of apocrine tumors had size less than 2 cm, compared with 71% of ductal tumors. After a median follow-up of 6.6 years no patients in the apocrine group experienced a breast cancer related event compared with 12 events (including 5 loco-regional recurrences, 3 distant recurrences e 4 contralateral tumors) in the ductal carcinoma group (Gray test p-value=0.015). Conclusions The outcome of selected apocrine triple negative breast cancer patients is excellent and possibly deserves a treatment de-escalation. Multicenter projects focusing on the possibility to avoid adjuvant chemotherapy in selected subtypes of triple negative breast cancers with favorable outcome are warranted. Legal entity responsible for the study The authors. Funding Has not received any funding. Disclosure G. Cancello: Honoraria (self): Pierre Fabre. E. Montagna: Honoraria (self): Pierre fabre; Honoraria (self): gentili. E. Munzone: Honoraria (institution), Advisory / Consultancy: Pierre Fabre; Honoraria (institution), Advisory / Consultancy: Genomic Health. S. Dellapasqua: Travel / Accommodation / Expenses: Roche. M.A. Colleoni: Advisory / Consultancy: Pierre Fabre; Advisory / Consultancy: Pfizer; Advisory / Consultancy: OBI Pharma; Advisory / Consultancy: Puma Biotechnology; Advisory / Consultancy: Celldex; Advisory / Consultancy: As