In patients with
hormone receptor positive
DCIS tamoxifen reduces recurrence rates by almost 50%. Few data are available with
aromatase inhibitors from randomised studies. In the ATAC study there were three
DCIS lesions in the
anastrozole arm and four in the
tamoxifen arm in the women with ER positive invasive
cancer. In the MA17 study which randomised patients to up to 5 years of
letrozole or placebo there was only one
DCIS event in the contralateral breast in patients taking
letrozole and five on placebo. There were also four patients in this study who had
DCIS in the conserved breast on placebo and none in the
letrozole treated group. The few clinical data that are available therefore suggest the
aromatase inhibitors are likely to be effective in
DCIS. A histological review of a study of 206 postmenopausal women with invasive oestrogen receptor positive
breast cancer who were randomised as part of a 14 day preoperative study to receive 2.5mg of
letrozole or 1mg of
anastrozole identified 27 patients with 28 pairs of tumours in whom there was sufficient ER positive
DCIS in invasive
cancer in the initial core biopsy and in the subsequent surgery specimen, to evaluate for PgR activity and proliferation. Within the
DCIS both
aromatase inhibitors significantly reduced PgR expression and both drugs also produced a significant fall in proliferation. There was a moderate degree of agreement between the fall in PgR in both the invasive
cancer and
DCIS (Kappa=0.5; p=0.0013) and between the fall in proliferation and between the invasive and in situ components (correlation coefficient=0.68; p<0.001). This study has shown significant effects of
aromatase inhibitors on
DCIS indicating that these agents are therapeutically active in this condition.