The cytochrome P450 family (CYPs) and the glutathione S-transferase (GSTs) enzymes play an important role in the metabolism of environmental carcinogens and of oestrogen and can affect breast cancer risk. In this study we examine the role of the genes CYP1A1, CYP17, CYP2D6, GSTM1, GSTP1 and GSTT1 in breast cancer risk in Brazilian women. The study population consisted of 102 incident breast cancer cases and 102 healthy controls. Genotyping analyses were performed by PCR-based methods. A significant finding was observed between GSTP1 Ile-Val polymorphism and breast cancer risk (OR = 1.81; CI 95% = 1.04-3.16). A significant association was observed between women with 0-2 risk genotypes and those with 4 or more risk genotypes (OR = 2.42; CI 95% = 1.13-5.18) when the potential combined effects of the risk genotypes were examined. No significant differences between cases and controls were found correlating the genotypes and the clinical-histopathological parameters. In conclusion, in our population only GSTP1 was associated with breast cancer risk. However, when the genes were tested in combination, a significant association in the breast cancer risk was observed.

MTAP is a ubiquitously expressed gene important for adenine and methionine salvage. The gene is located at 9p21, a chromosome region often deleted in breast carcinomas, similar to CDKN2A, a recognized tumor suppressor gene. Several research groups have shown that MTAP acts as a tumor suppressor, and some therapeutic approaches were proposed based on a tumors´ MTAP status. We analyzed MTAP and CDKN2A gene (RT-qPCR) and protein (western-blotting) expression in seven breast cancer cell lines and evaluated their promoter methylation patterns to better characterize the contribution of these genes to breast cancer. Cytotoxicity assays with inhibitors of de novo adenine synthesis (5-FU, AZA and MTX) after MTAP gene knockdown showed an increased sensitivity, mainly to 5-FU. MTAP expression was also evaluated in two groups of samples from breast cancer patients, fresh tumors and paired normal breast tissue, and from formalin-fixed paraffin embedded (FFPE) core breast cancer samples diagnosed as Luminal-A tumors and triple negative breast tumors (TNBC). The difference of MTAP expression between fresh tumors and normal tissues was not statistically significant. However, MTAP expression was significantly higher in Luminal-A breast tumors than in TNBC, suggesting the lack of expression in more aggressive breast tumors and the possibility of using the new approaches based on MTAP status in TNBC.

Previous studies have suggested the involvement of the 9p region in the genesis and progression of several types of cancer. To perform a more in-depth investigation of the 9p region in samples from breast carcinomas, we analyzed loss of heterozygosity (LOH) in 230 patients with primary breast cancer using five microsatellite markers spanning a genomic region of approximately 16.2 megabases. Genomic DNA was obtained from frozen tumor tissue, and peripheral blood was used as a normal reference. Among all samples, 171 (74%) were informative for at least 1 marker and 44 (25.73%) showed LOH. The LOH rates detected for all markers ranged from 10.29% (D9S169) to 15.97% (D9S1749). Among the informative cases for intragenic markers D9S1748 (CDKN2A) and D9S1749 (MTAP), we noticed a concordant loss of 90% (9/10). Associations between LOH frequencies and clinicopathologic parameters were found between marker D9S200 and tumor grade (P < 0.05), and between marker D9S1748 and estrogen receptor (ER) status (P < 0.05). In conclusion, our results agree with other data from the literature that point to LOH as a secondary mechanism of tumor suppressor inactivation on 9p in breast cancer, showing lower frequencies than those observed in other types of cancer. On the other hand, our results point to an interesting association between the concordant loss of genes CDKN2A and MTAP, which was not sufficiently explored in primary breast cancer.

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