174PAdjuvant chemotherapy in pT1ab node-negative triple negative breast carcinomas: Results of a national multi-institutional retrospective study

Background: Triple negative breast cancers (TNBC) are considered as associated with poor outcome, but prognosis of subcentimetric, node-negative disease remains controversial and evidence that adjuvant chemotherapy (CT) is effective in these small tumors remains limited. Methods: Our objective was to investigate the impact of adjuvant CT on survival in pT1abN0M0 TNBC. Patients were retrospectively identified from a cohort of 22,475 patients who underwent primary surgery in 15 French centers between 1987 and 2013. Since rare pathological types may display very particular prognoses in these tumors, we retained only the invasive ductal carcinomas of no special type according to the last WHO classification witch is most common TNBC histologic type. End-points were disease-free survival (DFS) and metastasis-free survival (MFS). A propensity score for receiving CT was estimated using a logistic regression including age, tumor size, SBR grade, and lymphovascular invasion. Results: Of a total of 284 patients with pT1abN0M0 ductal TNBC, 144 (51%) received post-operative CT and 140 (49%) did not. Patients receiving CT had more adverse prognostic features, such as tumor size, high grade, young age, and lympho-vascular invasion. Adjuvant CT was not associated with a significant benefit for DFS (Hazard ratio, HR = 0.77 [0.40-1.46]; p = 0.419, Log-rank test) or MFS (HR = 1.00 [0.46-2.19], p = 0.997), with 5-year DFS and MFS in the group with CT vs. without of 90% [81%-94%] vs. 84% [74%-90%], and 90% [81%-95%] vs. 90% [83%-95%], respectively. Results were consistent in all supportive analyses including multivariate Cox model and the use of the propensity score for adjustment and as a matching factor for case–control analyses. Conclusions: This study did not identify a significant DFS or MFS advantage for adjuvant CT in subcentimetric, node-negative ductal TNBC. Although current consensus guidelines recommend consideration of adjuvant CT in all TNBC larger than 5 mm, clinicians should carefully discuss benefit/risk ratio with patients, given the yet unproven benefits. Legal entity responsible for the study: SIRIC program (INCa-DGOS-Inserm 6038) Funding: SIRIC program (INCa-DGOS-Inserm 6038) Disclosure: All authors have declared no conflicts of interest.