A recent joint analysis from the NSABP B-24 and the NSABP B-17 studies evaluating 818 patients in total with DCIS who had conservative surgery, randomized to RT alone or complementary follow-up, documented a significant increase of the risk of death in cases of recurrent ipsilateral invasive cancer and found no association between DCIS recurrence and mortality. In addition, there was no difference in survival (global and breast cancer-related) among the different treatment groups: surgery, surgery + RT, and surgery + RT + TMX [3].

In 2011 an update of the results of a second study of UK/ANZ DCIS stage (the UK, Australia, and New Zealand ductal carcinoma in situ) was published, evaluating the role of RT and/or TMX in patients treated with conservative surgery for DCIS. The study enrolled 1701 patients, with the aim of analyzing the following therapeutic approaches: surgery alone, surgery followed by RT, surgery followed by RT and TMX (20 mg/daily for 5 years), and surgery followed by TMX (20 mg/daily for 5 years). In the arms treated with TMX, over a median of 12.7 years of follow-up, a significant reduction of all breast events (HR = 0.71; 95% CI 0.58–0.88; p = 0.002. Figure 11.2), of the risk of ipsilateral DCIS (HR = 0.70; 95% CI 0.51–0.86; p = 0.03), and of contralateral tumors (HR = 0.44, 95% CI 0.25 to 0.77; p = 0.005) was showed [4].

However, no difference in the incidence of ipsilateral invasive relapse in the various treatment groups was highlighted. Moreover, the subgroup analysis showed some benefit related to TMX in patients’ group treated with surgery alone but not in the other subgroups, including the arm combining surgery with RT + TMX (Fig. 11.3).

A recent combined analysis of NSABP-B24 trial and UK/ANZ19 concluded that TMX after breast- conserving surgery and radiation therapy led to a risk reduction of invasive ipsilateral breast cancer (pooled RR = 0.61; 95% CI 0.41–0.92) and contralateral DCIS (RR = 0.4; 95% CI 0.16–0.96), independently from the age; moreover, tamoxifen had no impact on overall survival or on breast cancer-related mortality [5].

In conclusion, whether or not to offer TMX in DCIS treatment should be based on an individual analysis between benefits and expected side effects. TMX may be considered for treatment of hormone receptor-positive DCIS either in the premenopausal or in the postmenopausal setting. Standard treatment lasts 5 years.

Currently there are several ongoing clinical trials aimed to assess the efficacy of endocrine therapy in DCIS. Nowadays, the treatment with aromatase inhibitors remains approved only in invasive breast cancer setting. In fact, there is still a lack of data regarding the use of aromatase inhibitors in the treatment of DCIS.