Assessment of hormone dependence of comedo ductal carcinoma in situ of the breast.

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Abstract
Background: Ductal carcinoma in situ (DCIS) represents 20%-30% of breast cancers detected by clinical screening (i.e., mammography). More than 50% of DCIS lesions may be estrogen receptor negative and, therefore, hormone independent. However, the role of estrogen in the natural history of DCIS is unknown. Purpose: A novel in vivo (i.e., xenograft) model was developed to determine to what degree DCIS lesions depend on estrogen for growth. Methods: Specimens of breast tissue were collected from 52 women during diagnostic or therapeutic surgical procedures. Portions of each specimen were randomly selected and analyzed by histology and thymidine labeling (to measure cell proliferation). The remainder of each specimen was implanted into five to 18 athymic BALB/c nu/nu mice (depending on the amount of tissue available), with eight pieces of approximately 2 mm × 2 mm × 1 mm implanted at different locations on the back of each mouse. Half of the mice received implants containing estrogen (2 mg 17β-estradiol), and the other half received placebo implants. Levels of cell proliferation in xenografts, recovered after 14, 28, 42, or 56 days in the mice, were measured by thymidine labeling or by immunohistochemistry through use of an antibody specific for the Ki-67 nuclear antigen. Immunohistochemistry was also used to measure the levels of estrogen receptor in the tissue specimens. Serum 17β-estradiol levels in the mice were measured by radioimmunoassay. Results: Initial levels of cell proliferation were approximately 10-fold higher in 10 specimens with estrogen receptor-negative, comedo (i.e., more malignant in appearance) DCIS than in four specimens with estrogen receptor-positive DCIS (mean proliferation indices: 22% versus 1.9%, respectively; two-sided P <.001). Xenografts from the majority of specimens survived up to 56 days in the mice and maintained good architectural and cellular preservation. Estrogen treatment of the xenograft-bearing mice had no effect on the high level of cell proliferation observed in estrogen receptor- negative, comedo DCIS specimens (two-sided P = .89). In contrast, increased levels of cell proliferation in response to estrogen supplementation were measured in three estrogen receptor- positive, noncomedo DCIS specimens (two-sided P <.001). However, even with estrogen treatment, cell proliferation levels in estrogen receptorpositive DCIS specimens did not reach those seen in estrogen receptornegative DCIS specimens. Conclusion and Implication: Estrogen receptornegative, comedo DCIS lesions appear to be estrogen independent; therefore, antiestrogen (e.g., tamoxifen) therapy may not benefit patients with comedo DCIS.