BACKGROUND:

We have shown previously that lumpectomy with radiation therapy was more effective than lumpectomy alone for the treatment of ductal carcinoma in situ (DCIS). We did a double-blind randomised controlled trial to find out whether lumpectomy, radiation therapy, and tamoxifen was of more benefit than lumpectomy and radiation therapy alone for DCIS.

METHODS:

1804 women with DCIS, including those whose resected sample margins were involved with tumour, were randomly assigned lumpectomy, radiation therapy (50 Gy), and placebo (n=902), or lumpectomy, radiation therapy, and tamoxifen (20 mg daily for 5 years, n=902). Median follow-up was 74 months (range 57-93). We compared annual event rates and cumulative probability of invasive or non-invasive ipsilateral and contralateral tumours over 5 years.

FINDINGS:

Women in the tamoxifen group had fewer breast-cancer events at 5 years than did those on placebo (8.2 vs 13.4%, p=0.0009). The cumulative incidence of all invasive breast-cancer events in the tamoxifen group was 4.1% at 5 years: 2.1% in the ipsilateral breast, 1.8% in the contralateral breast, and 0.2% at regional or distant sites. The risk of ipsilateral-breast cancer was lower in the tamoxifen group even when sample margins contained tumour and when DCIS was associated with comedonecrosis.

INTERPRETATION:

The combination of lumpectomy, radiation therapy, and tamoxifen was effective in the prevention of invasive cancer.