Breast cancer is one of the most common types of cancer among women worldwide. The TMPRSS6 (Transmembrane Serine Protease 6) gene encodes matriptase-2, which plays an important role in iron hemostasis as the hepcidin regulator and may play a role in breast cancer susceptibility. In this study, we examined the expression levels of the TMPRSS6 gene in healthy tissues and tumor tissues of breast cancer patients; and the relationship between these levels and pathological findings. The relationship between TMPRSS6 polymorphisms (rs733655, rs5756506, rs2413450, rs855791, rs2235324, rs4820268) and patients' hematological parameters. The gene expression study encompassed 47 breast cancer patients and the gene polymorphism study consisted of 181 breast cancer patients and 100 healthy controls. Gene expression analysis was performed by qRT-PCR. The genotyping of TMPRSS6 polymorphisms was performed by RT-PCR. TMPRSS6 gene expression levels in tumor tissues were found to be 1.88 times higher than the expression levels in the control tissues. We examined the relationship between TMPRSS6 gene expression levels and pathological data, statistically significant relationship was found between patient's estrogen receptor (ER) and HER2 findings and TMPRSS6 gene expression (respectively p = 0.02, p = 0.002). When the relationship between TMPRSS6 gene polymorphisms related genotypes distributions and hematological findings was investigated, a significant relationship was identified between mean corpuscular hemoglobin concentration (MCHC) parameter and the polymorphism of only the rs733655. According to our findings, the increase in TMPRSS6 gene expression in cancerous tissues shows that matriptase-2 may be effective in the cancer process. Thus TMPRSS6 gene polymorphisms may affect the disease process by affecting the blood parameters of patients.