Triple-negative breast cancers (TNBCs) 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 tumours remains limited.

Our objective was to investigate the impact of CT on survival in pT1abN0M0 TNBC. Patients were retrospectively identified from a cohort of 22,475 patients who underwent primary surgery in 15 French centres between 1987 and 2013. As rare pathological types may display very particular prognoses in these tumours, we retained only the invasive ductal carcinomas of no special type according to the last World Health Organisation (WHO) classification which is the most common TNBC histological 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, tumour size, Scarff Bloom and Richardson (SBR) grade and lymphovascular invasion.

Of a total of 284 patients with pT1abN0M0 ductal TNBC, 144 (51%) received CT and 140 (49%) did not. Patients receiving CT had more adverse prognostic features, such as tumour size, high grade, young age, and lymphovascular invasion. 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 versus without of 90% [81-94%] versus 84% [74-90%], and 90% [81-95%] versus 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.

This study did not identify a significant DFS or MFS advantage for CT in subcentimetric, node-negative ductal TNBC. Although current consensus guidelines recommend consideration of CT in all TNBC larger than 5 mm, clinicians should carefully discuss benefit/risk ratio with patients, given the unproven benefits.