None of the chemopreventive agents used, alone or in combination, were found to affect expression of any of the TGF-β isoforms or the LTBP in either ductal epithelium or periductal stroma after 6 weeks of chemopreventive intervention (Fig. 3). The 6-week time point was chosen as representative of the period of preneoplasia, as the majority of the animals had no palpable tumors at this time (Fig. 1). In the study set, eight out of 36 (22%) of the slides showed histologic evidence of hyperplasia, one out of 36 had a ductal carcinoma in situ (mammary intraepithelial neoplasia [22]), and one out of 36 had a carcinoma. We further investigated the effect of tamoxifen at higher doses and earlier time points. In rats that received tamoxifen at 10 mg/kg per day intragastrically (equivalent to 600 mg/day for a human) or 1 mg/kg per day intragastrically (equivalent to 60 mg/day for a human) for either 1 day or 3 weeks, again no consistent changes were seen in TGF-β expression, using either the TGF-β1-CC or the TGF-β2 antibodies (data not shown).