In this case-control study, we found essential data on blood group distribution and prognostic significance in MBC patients. Although we found that the AB blood group was more common in male breast cancer patients, we showed that it was not a prognostic factor for overall survival. Since the 1960s, researchers have studied the link between ABO blood groups and cancer. Blood type A was associated with an excess risk of developing stomach  and pancreatic cancer . Blood type AB was associated with an increased risk of developing nasopharyngeal carcinoma  and postmenopausal ovarian cancer . Also, B Blood type was found as a risk factor for ovarian  and esophageal cancer development . In our study, we found that the AB blood group ratio was 2.4 and the O blood group ratio 0.62 in male breast cancer patients compared to the healthy population. A meta-analysis found that blood type A may have a higher risk than other blood groups in FBC . But, Yuksel et al. did not detect any link between HER2 positive breast cancer and ABO blood type or Rh factor .
The underlying mechanisms of the ABO blood group with cancer development and progression are still poorly understood. The variant alleles (O, B, and A) of a single gene are located on chromosome 9q34. Genetic variants of the ABO locus may play a role in cancer development . Blood groups are carbohydrate antigens found on the surface of epithelial cells such as epidermis, genital tract, bronchopulmonary, and gastrointestinal cells . The blood type isoantigens are constantly expressed in healthy breast tissue, but the A and B isoantigens are likely to disappear in breast cancer . In addition, the antigens of the ABO blood type may affect the host's inflammatory response, and persistent inflammation may lead to cancer formation .
Many studies have been assessed the relationship between ABO blood group antigens and survival in various types of cancers. Although the results of studies on the prognostic importance of the blood group are still controversial, statistically significant results were obtained in some studies involving a high number of patients. According to Fukumoto et al.’s results that ABO blood type was a significant prognostic factor in resected non-small cell cancer patients. The patients with blood type O had higher 5-year overall and disease-free survival rates than patients with other ABO blood groups . Sun et al. discovered that the A blood group was significantly associated with an increased mortality ratio (HR, 1.38 95 percent CI) compared to the O blood group in gastric cancer after adjusting for demographic and clinical features . Similarly, Xu et al. found that blood type AB is a favorable prognostic factor for gastric cancer patients, but blood type A is an unfavorable prognostic factor for gastrectomy patients . In FBC, data on the prognostic significance of the ABO blood group is unclear and contradictory. In a prospective study, Gates et al. found no evidence of a link between blood type and overall or breast cancer-specific survival. The hazard ratios of death due to any cause were 1.00 for blood type A, 1.35 for AB, and 0.81 for B, compared to patients with blood type O . Inversely, in a study that included non-metastatic breast cancer patients, when comparing with A and O blood types to those with other blood groups, it was shown that overall and disease-free survival periods were longer in the A and O blood groups . In a nationwide study from the Kore, breast cancer patients with blood type O had a better prognosis when they were less than 40 years old than patients with blood group non-O . Also, Yu et al. showed that Triple-Negative Breast Cancer (TNBC) and its prognosis were not linked to a particular ABO blood type or Rh factor status . In our study, the ABO blood group’s prognostic significance was not found in MBC patients. The Rh factor was detected as a statistically significant prognostic factor in univariate analysis, but it was probably biased and not confirmed in multivariate analysis.
The relationship between the blood group distribution of the patients and their clinicopathologic features has been investigated in different cancer types. In gastric cancer, Yu H et al. found no link between ABO blood types and clinicopathological characteristics. Furthermore, Qiu et al. found no significant variations by ABO blood type in gastric cancer in terms of gender, tumor size, differentiation degree, P53 status, or tumor stage . Data on the relationship between breast cancer clinicopathological features and ABO/Rh blood group is limited. According to the results of the retrospective study published by Serkan et al.; the type, grade, stage, and hormonal state of breast cancer had no significant relationships with ABO blood grouping . Similarly, we could not find a relationship between blood group characteristics and the age at diagnosis, tumor stage, histopathologic features, and BRCA mutation status of male breast cancer patients.
Our study was a multi-center study. The study's limitations were the small number of patients due to being a rare tumor and its retrospective design. In addition, some data were missing and may have biased the statistical analysis.