Abstract P1-15-03: Eight-Year Update of a Prospective Study of Wide Excision Alone for Ductal Carcinoma In Situ (DCIS) of the Breast

Abstract Background: The need for radiation therapy (RT) in conservatively managed DCIS is a source of ongoing debate. This is an updated analysis of a phase II prospective study of wide excision alone for DCIS. The study was activated in May 1995 and closed in July 2002 following accrual of 158 patients because the number of local recurrences (LR) met the predetermined stopping rules. The objective of the analysis is to update the distribution and cumulative incidence of events (LR, contralateral breast cancer [CBC], second malignancy and death from other causes). Materials and Methods: A total of 158 patients had DCIS with predominant nuclear grade 1 or 2, a mammographic extent of ≥2.5 cm, and excision with final microscopic margins of ≥1 cm or a re-excision without residual DCIS. Tamoxifen was not permitted. The results presented are from the 8-year analysis (8-year minimum potential follow-up time). Twenty-six patients without recurrence who were followed less than 8 years were excluded from the analysis as were 7 first events (4 LR) that occurred beyond 8 years of follow-up; the analysis thus includes 132 patients and 36 first events. Cumulative incidence curves were generated to assess the rates of LR or other events. Median follow up time was 10 years. Results: Overall, 36/132 patients (27%) had a first event as of April 2010. Of these 36 events, 19 were LR, 13 were CBC, 1 was a second malignancy, and 3 were deaths from other causes. Of the 19 LR, 13 (68%) were DCIS only and 6 (32%) were invasive. Fourteen occurred in the same quadrant and 5 were elsewhere in the ipsilateral breast. The 8-year estimated cumulative incidence of LR was 14.4% (95% CI: 8.4-20.4%). For all other events, the 8-year estimated cumulative incidence was 12.9% (95% CI: 3.6-13.1%). The estimated annual percentage rates of LR, CBC, and other events were 2.1%, 1.5% and 0.4%, respectively. Discussion: The results of this prospective study demonstrate a substantial and ongoing risk of LR and CBC in patients with small, nuclear grade 1 or 2 DCIS treated with wide excision with margins of ≥1cm in the absence of RT. Most LRs occurred in the same quadrant, rather than elsewhere in the breast, suggesting that excision alone is inadequate even for this highly selected population. Further study is warranted to determine if there is a subgroup of DCIS patients with nuclear grade 1 or 2 disease who are at low enough risk of LR following wide excision that RT can be omitted safely. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P1-15-03.