Adjuvant trastuzumab for small, node-negative, human epidermal growth factor receptor 2 (HER2)-positive breast cancer remains controversial. The purpose of this study was to investigate the risk of recurrence in women with pathological tumour node (pTN) T1 N0 tumours.

Patients with pT1 N0 breast cancer diagnosed at the National Kyushu Cancer Centre between 2001 and 2007 were reviewed. Patients were categorized according to HER2 status.

Four hundred and fifty-four patients who had pT1 N0 tumours, and had not received adjuvant trastuzumab, were identified. The HER2-negative and -positive groups comprised 376 and 78 patients (17·2 per cent) respectively. At a median follow-up of 46·3 months, there were 18 recurrences. The 5-year relapse-free survival (RFS) rates were 97·2 and 88 per cent in the HER2-negative and -positive groups respectively (P < 0·001). Multivariable analysis identified HER2-positive tumour as an independent predictor of RFS in patients with pT1 N0 tumours (hazard ratio 6·65, 95 per cent confidence interval 2·53 to 17·49; P < 0·001).

Women with pT1 N0 HER2-positive breast cancer have a high risk of recurrence.