Abstract Recent data from our laboratory show that the follicle-stimulating hormone receptor (FSHR) is expressed on the endothelial surface of tumor peripheral blood vessels in different types of tumors including breast cancer. The main goal of the present study was to determine differences in the endothelial FSHR expression level among the breast cancer types, and within the same tumor type, among tumor stages. We have also compared the FSHR expression with the receptor status of three most important markers for breast cancer diagnosis and therapy (estrogen receptor, progesterone receptor, and HER-2/neu). By using a highly specific monoclonal antibody raised against the human FSHR, we determined the density of FSHR-positive vessels in a band with a width of 10 mm (centered on the demarcation line between the tumor and the normal breast tissue) on the tissue sections by standard peroxidase-immunohistochemistry and immunofluorescent confocal microscopy. We examined 35 patients of Luminal A, 13 patients of Luminal B, 19 patients of HER-2 positive, and 16 patients of Triple negative/basal breast cancer. All four groups expressed almost similar densities of FSHR stained blood vessels with 36.7 ± 4.0/mm2 in Luminal A, 31.4 ± 5.2/mm2 in Luminal B, 39.6 ± 6.0/mm2 in HER-2 positive tumors, and 38.4 ± 8.0/mm2 in triple negative/basal group. A positive correlation has been observed between the percentage of FSHR-positive vessels and total blood vessels in the tumor periphery (r = 0.551; p = 7e-08). We have also noticed a tendency (not reaching statistical significance) towards an overall decrease in the extent of the vascular bed in elder patients as compared to younger patients. No correlation was found between the percentage of FSHR-positive vessels and the expression of receptors for estrogen, progesterone, and HER-2/neu. In conclusion, our data show that: (i) FSHR is robustly expressed in breast cancer, and (ii) the main types of breast cancers and stages do not differ significantly in terms of vascular FSHR expression. These facts strongly increase FSHR potential relevance as a clinical target for breast cancer imaging and for therapy, especially for triple negative/basal breast cancers, a group with only chemotherapy options. Citation Format: François Planeix, Mohammad-Ahsan Siraj, François-Clément Bidard, Jean-Yves Pierga, Xavier Sastre, Martine Antoine, Nicolae Ghinea. Assessment of FSH receptor expression in the major molecular subtypes of breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 7. doi:10.1158/1538-7445.AM2014-7