Aim The earlier detection of breast cancer through mammographic screening has resulted in a shift in stage distribution with patients who are node-positive tending to present with a lower number of positive lymph nodes (LN). This study aims to assess the prognostic value of absolute number of positive nodes in the pN1 TNM stage (1–3 positive LN) and whether the prognostic value of the number of nodes in this clinically important stage justifies its consideration in management decisions.

Methods This study is based on a large and well-characterised consecutive series of operable breast cancer (3491 cases), treated according to standard protocols in a single institution, with a long-term follow-up.

Results LN stages and the absolute number of LN are associated with both breast cancer specific survival (BCSS) and distant metastasis free survival (DMFS). In the pN1 stage, patients with three positive LN (14% of pN1) show shorter BCSS (HR=1.9, (95% CI 1.3 to 2.6)) and shorter DMFS (HR=2.2, (95% CI 1.6 to 2.9)) when compared with one and/or two positive nodes. This effect is noted in the whole series as well as in different subgroups based on tumour size (pT1c and pT2), histological grade (grade 2 and 3), vascular invasion and oestrogen receptor status (both positive and negative). Multivariable analyses showed that three positive LN, compared with one and two positive LN, are an independent predictor of shorter BCSS and DMFS.

Conclusion The number of LN in the pN1 stage yielded potentially informative risk assignments with three positive LN providing an independent predictor of poorer outcome.