Effects of a pure antiestrogen on apoptosis and proliferation within human breast ductal carcinoma in situ.

Adjuvant antiestrogen (AE) therapy has been proposed for all women with ductal carcinoma in situ (DCIS). However, many cases of DCIS are of the high-grade, estrogen receptor (ER)-negative subtype that are unlikely to respond to AE treatment. Hormonal agents work by increasing apoptosis and/or decreasing cell proliferation; therefore, we studied the effect of a pure AE on levels of apoptosis and proliferation in human DCIS xenografts using an in vivo model. Women (n = 23) with mammographic microcalcification suggestive of DCIS were identified at the time of surgery (day 0), a sample of representative tissue was obtained, divided into multiple 2x2x1-mm xenografts, and implanted s.c. into female BALB/c nu/nu mice (eight xenografts/mouse). Day 0 grafts underwent immunohistochemical assessment of ER status. Fourteen days after implantation, four xenografts were retrieved and mice were randomly divided into one of three treatment groups: (a) insertion of a slow release 2-mg 17beta-estradiol pellet; (b) weekly 5-mg injections of the pure AE Faslodex (Zeneca Pharmaceuticals); and (c) injections of a control vehicle oil alone. After 2 weeks of treatment, the remaining four xenografts were retrieved from each mouse. Retrieved xenografts containing DCIS were assessed for morphological evidence of apoptotic cell death [apoptotic index (AI)] and cell proliferation (by immunohistochemical detection of the Ki67 proliferation antigen LI). Both AI and LI were higher in the day 0 specimens of 16 ER- DCIS lesions compared with 7 ER+ DCIS lesions (mean values, 1.47% versus 0.32% and 20.6% versus 3.1%; both P<0.0001). AI and LI values within ER- DCIS did not differ between xenografts exposed to 17beta-estradiol or AE treatment compared with the controls or pretreatment values (mean AI and LI in estradiol-treated, antiestrogen-treated, and control groups 1.04% versus 0.98% versus 1.29% and 17.2% versus 20.5% versus 17.7% respectively). In contrast, treatment of mice bearing ER+ DCIS xenografts with 17beta-estradiol raised both the AI (1.03% versus 0.40%, P = 0.03) and LI (11.0% versus 5.1%, P = 0.007) compared with controls. AE therapy of ER+ DCIS xenografts did not affect proliferation but resulted in higher apoptosis than in controls (0.9% versus 0.4% respectively, P = 0.04). AE therapy should be reserved for patients with estrogen receptor positive DCIS.