To observe the impact of internal mammary node irradiation (IMNI) on disease-free survival (DFS) and overall survival (OS) in postmastectomy women with breast cancer.

Between 1978 and 1996, 153 women with stage II–III breast cancer were treated with postmastectomy radiation therapy (RT) with IMNI. Their clinical, pathological and treatment characteristics were matched with 166 patients without IMNI. The RT dose was 35 Gy to the chest wall and 40 Gy to the supraclavicular fossa and IMN in 15 fractions over 3 weeks with photons. All patients were planned with two-dimensional technique. Adjuvant chemotherapy was administered to 41% and endocrine therapy to 52% of the patients. Symptomatic patients were further assessed for late pulmonary and late cardiac effects.

The median follow-up period was 203 months (range, 182–224), and the median age was 44 years (range 20–73 years). The IMNI group had significantly more right-sided and inner/central quadrant tumours. Other characteristics were comparable between both the groups. DFS at 15 years with and without IMNI was 64 and 49%, respectively (p=0·0001). On multivariate analysis, IMNI was an independent, positive predictor of DFS [hazard ratio (HR), 2·89; p=0·0001]. Benefit of IMNI on DFS was more apparent in inner/central tumours [HR, 1·48; 95% confidence interval (CI), 1·02–2·88], N2–N3 patients (HR, 1·44; 95% CI, 1·09–2·10) and in those who received chemotherapy (HR, 1·70; 95% CI, 1·07–2·71). OS at 15 years with and without IMNI was 68 and 54%, respectively (p=0·0001). Late pulmonary toxicity was 1·5 versus 1% with and without IMNI, respectively. Late cardiac toxicity was 2·6 versus 1·8% with and without IMNI, respectively.

IMNI significantly improved DFS and OS in postmastectomy breast cancer patients. Benefit of IMNI was seen in patients with central/inner tumours and N2–N3 disease. Late cardiopulmonary toxicities were comparable between the two groups.