Background

As a consequence of mammographic breast screening programmes, ductal carcinoma in situ is diagnosed with increasing frequency. Mastectomy for localised ductal carcinoma in situ is thought to be an overtreatment by many physicians, but there is much controversy as to whether complete local excision alone is sufficient. We aimed to assess the effectiveness of adjuvant radio-therapy and tamoxifen.

Methods

We used a 2×2 factorial design in a randomised controlled trial. Between May, 1990, and August, 1998, 1701 patients recruited from screening programmes were randomised to both treatments in combination or singly, or to none, or to either one (eg, radiotherapy) with an elective decision to give or to withhold the other (i.e., in this case tamoxifen). Patients had complete surgical excision of the lesion con-firmed by specimen radiography and histology. Patients have been followed up at least once a year. Median follow-up was 52·6 (range 2·4–118·3) months. Our primary endpoint was the incidence of ipsilateral invasive disease.

Findings

Ipsilateral invasive disease was not reduced by tamoxifen but recurrence of overall ductal carcinoma in situ was decreased (hazard ratio 0·68 [0·49–0·96]; p=0·03). Radiotherapy reduced the incidence of ips-ilateral invasive disease (0·45 [0·24–0·85]; p=0·01) and ipsilateral ductal carcinoma in situ (0·36 [0·19–0·66]; p=0·0004), but there was no effect on the occurrence of contra-lateral disease. There was no evidence of interaction between radiotherapy and tamoxifen.

Interpretation

Radiotherapy can be recommended for patients with ductal carcinoma in situ treated by complete local excision; however, there is little evidence for the use of tamoxifen in these women.