Since 1985, 5411 patients were randomized in four large randomized clinical trials assessing the role of adjuvant radiotherapy and/or tamoxifen in breast conserving surgery for patients with ductal carcinoma in situ (DCIS).
First the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-17 trial proved relevance of postoperative radiotherapy in breast conserving surgery in DCIS patients: an approximately 50% reduction of ipsilateral tumour recurrences. This is confirmed by longer time of follow-up and validated by data from the European Organization for Research and Treatment of Cancer (EORTC) 10853 and UK Coordinating Committee on Cancer Research (UKCCCR) DCIS trials. A subset of patients who do not benefit of adjuvant radiotherapy cannot be identified. Completeness of excision proved to be the most important treatment variable to reduce local recurrence.
Both the NSABP B-24 and UKCCCR DCIS trials investigated the effect of tamoxifen resulting in contradictory findings. In addition a possible benefit seems to be restricted to oestrogen receptor-positive DCIS lesions nourishing the existent reserve in prescribing tamoxifen for all patients with DCIS.
The failure to materialize a difference in survival by the effect of either adjuvant radiotherapy or tamoxifen endorses the favourable outcome of DCIS. Currently, four other randomized clinical trials investigate the role of radiotherapy, tamoxifen, anastrazole, or no further treatment for a selected group of patients.