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The development of the mammary gland is a hormone-regulated event. Several factors can dysregulate its growth and make the gland more susceptible to cellular transformation. Among these factors, perinatal exposure to xenoestrogens and hormone replacement therapy has been associated with increased risk of developing breast cancer. Here, we assessed the effects induced by estrogen replacement therapy (ERT) in ovariectomized (OVX) middle-aged rats and whether perinatal exposure to diethylstilbestrol (DES) or bisphenol A (BPA) modified these effects in the mammary gland. Pregnant rats were orally exposed to vehicle, 5 μg DES/kg/day, or 0.5 or 50 μg BPA/kg/day from gestational day 9 until weaning. Then, 12-month-old offspring were OVX and treated with 17β-estradiol for 3 months. Morphological changes and the percentage of epithelial cells that proliferated or expressed estrogen receptor alpha (ESR1) and progesterone receptor (PR) were analyzed in mammary gland samples of 15-month-old animals. ERT induced lobuloalveolar hyperplasia and ductal cysts in the mammary gland of middle-aged rats, associated with a higher proliferation index of epithelial cells. Perinatal exposure to DES followed by ERT increased the number of cysts and induced the formation of fibroadenoma and ductal carcinoma in situ, without modifying the expression of ESR1 or PR. Also, after 3 months of ERT, BPA-exposed rats had a higher incidence of ductal hyperplasia and atypical lobular hyperplasia than animals under ERT alone. In conclusion, perinatal exposure to xenoestrogens increases the susceptibility of the mammary gland to develop cysts and hyperplastic lesions when confronted with ERT later in life.

Our aim was to evaluate whether postnatal exposure to a glyphosate-based herbicide (GBH) modifies mammary gland development in pre- and post-pubertal male rats. From postnatal day 1 (PND1) to PND7, male rats were injected subcutaneously every 48 h with either saline solution (vehicle) or 2 mg GBH/kg·bw. On PND21 and PND60, mammary gland and blood samples were collected. Estradiol (E2) and testosterone (T) serum levels, mammary gland histology, collagen fiber organization, mast cell infiltration, proliferation index, and estrogen (ESR1) and androgen receptor (AR) expression levels were evaluated. At PND21, GBH-exposed male rats exhibited greater development of the mammary gland with increased stromal collagen organization and terminal end buds (TEBs) compared to control rats. At PND60, the number of TEBs remained high and was accompanied by an increase in mast cell infiltration, proliferation and ESR1 expression in GBH-exposed male rats. In contrast, no effects were observed in E2 and T serum levels and AR expression in both days studied. Our results showed that a postnatal subacute treatment with GBH induces endocrine-disrupting effects in the male mammary gland in vivo, altering its normal development.

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590 Background: Polymorphisms in cytochrome P450 2D6 gene affect the plasma concentration of tamoxifen active metabolites (endoxifen). Some drugs are known to be CYP2D6 inhibitors. We aim to determine the relationship between CYP2D6*4 polymorphisms, concomitant CYP2D6 inhibitors use and clinical outcomes of breast cancer patients receiving adjuvant tamoxifen (TAM). Patients and Methods: CYP2D6*4 (1934 G>A+1) genotype was determinated from DNA of blood samples using PCR-RFLP technique and Taqman Allelic Discrimination Assay in a series of 84 breast cancer patients receiving adjuvant TAM. CYP2D6 inhibitors were recorded. Chi-square test and logistic regression models were used to determinate association between genotype, use of concomitant CYP2D6 inhibitors and disease relapse rate. Results: In our 84 patients series mean age was 51.5y. (33–71). 14.8% were stage I, 58.0% stage II and 27.2% stage III. 61.4% were nodes positive and 98.7% tumors had positive hormonal receptors. We observed disease recurrence in 36.9% of cases. The mean following-up was 5.5 y. Genotype frequency was: wt/wt (57.1%), wt/*4 (40.5%) and *4/*4 (2.4%). 50% (18 of 36) of patients with the wt/*4 + *4/*4 genotypes had disease relapse compared with 27% (13 of 48) with wt/wt genotype (P= 0.041). Only 6 patients received concomitants CYP2D6 inhibitors, mainly antidepressants, all of them with the wt/*4 genotype. 50% presented disease relapse. Clinical pathological variables were evaluated and significant relation was found between stage and disease relapse by univariate analysis (P= 0.001). We investigated whether CYP2D6*4 genotype and stage to diagnosis could influence in disease relapse. For these analyses we use as reference group the genotype wt/wt. We observed that combined genotype wt/*4 + *4/*4 was more strongly associated with disease recurrence than wt/wt genotype (adjusted hazard ratio [HR], 2.82, 95% confidence interval [CI] 1.0- 7.9) P= 0.049. Conclusions: Breast cancer patients with the CYP2D6 *4/*4 or wt/*4 genotype could have lower benefit of TAM adjuvant treatment and tend to have a higher risk of disease relapse. Pre-treatment CYP2D6 genotype determination from blood sample could predicts TAM clinical outcomes and help to oncologist in treatment decision. No significant financial relationships to disclose.

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