The increased risk of breast cancer dissipates within 2 years after finishing HRT [33]. 50–70% of all invasive breast cancers are invasive ductal tumors, which arise in the milk ducts of the breast. According to the expression pattern of specific genes, cancers are further subdivided into four major molecular subtypes: luminal A, luminal B, triple negative/basal-like, and HER2 type tumors. Both luminal A and Inhibitors,research,lifescience,medical luminal B tumors express ERs, while the triple negative/basal-like tumors and HER2-type tumors are negative for ERs and PGs. Lobular see more carcinomas (10–20%) start from

cells in the lobuli and can also be divided in these subtypes [34]. The luminal A breast cancer is the most common subtype, representing 50–60% of the total. It is characterized by the expression of ER targeted genes that are typically present in the luminal epithelium lining the mammary ducts, absence of HER2, a low proliferation rate, and a low histological grade. Based on their molecular profile, Inhibitors,research,lifescience,medical all cases of lobular carcinoma in situ and most

of the infiltrating lobular carcinomas belong to this subtype. Luminal B molecular profile tumors (10%–20% of all breast cancers) are more aggressive, have a higher histological Inhibitors,research,lifescience,medical grade, and a worse prognosis [35]. Several data show that estrogens are enriched in breast cancer tissue as compared to normal tissue. They surplus the plasma levels by 23-fold in women at reproductive age and 23-fold in postmenopausal patients. In older women, nearly all E2 is locally produced,

but also in younger women up to 75% originate from the local production [35]. Inhibitors,research,lifescience,medical In breast cancer, the STS pathway with the reduction of E1 to E2 is catalyzed by reductive 17beta-HSDs. This is Inhibitors,research,lifescience,medical the most prominent pathway and prevail the aromatase pathway with estrogen production from testosterone and its precursors by 50–200-fold [6]. Indeed, many studies showed that STS activity is much higher than aromatase activity in breast tumors, the activity of the enzyme is also higher in the carcinoma than in the nonmalignant tissue, and expression of tissue-specific transcripts of STS is controlled by ERalpha signaling in normal and cancerous breast tissue [36]. Studies in patients with ERalpha-positive breast cancer showed that expression of more active STS isoforms under estrogen therapy may cause upregulation of E2, which would further promote cancer progression second [36]. Moreover, high levels of STS mRNA expression in tumors are associated with a poor prognosis [37]. Breast tumors expressing ERs may benefit from adjuvant endocrine therapy with antiestrogens such as tamoxifen, which is applied in pre- and postmenopausal women. In postmenopausal women blocking the estrogen production by inhibitors of estrogen formation, for example, aromatase inhibitors is an effective therapy for cancer prevention [38, 39].