Besides known prognostic factors in breast cancer, disseminated tumor cells are regarded as a surrogate marker for minimal residual disease in breast cancer. Their prognostic significance is comparable to that of lymph node status. However, the mechanism by which the primary tumor directs cells to disseminate into lymph nodes or into blood vessels is unclear. Aquaporins (AQPs) are small integral membrane proteins that provide a major pathway for water transport throughout several organs, and have been shown to be of potential importance in various types of cancer. Here, we analyzed the single nucleotide polymorphism (SNP) A(−1364)C in AQP5 in 107 patients with early stage breast cancer in order to test the hypothesis that this polymorphism is associated with lymphogenous and hematogenous tumor cell dissemination and overall survival. Paraffin-embedded tumor tissue was dewaxed, and DNA was extracted from tumor tissues using the QIAamp Blood DNA Mini Kit. The quantification and quality of the extracted DNA were determined spectrophotometrically. Genotyping of the −1364A>C polymorphism was performed by Pyrosequencing. Cytokeratin-positive (CK+) bone marrow (BM) cells were isolated by density gradient centrifugation followed by immunocytochemistry, applying the pan CK antibody A45-B/B3. There was no evidence of an association between the AQP5C>A genotypes and an increased risk of developing breast cancer, nor between the genotypes and tumor size, lymph node involvement, distant metastasis, grade, histopathology, expression of estrogen receptor and HER2, or the dissemination of tumor cells to BM. In contrast, when comparing C-allele carriers with patients carrying the AA genotype, expression of the progesterone receptor differed significantly between these genotype groups (mean AA genotype 51%, mean AC and CC genotype 73%; p=0.039). Additionally, a significant correlation was found between progesterone receptor expression and adjuvant chemotherapy (p=0.021) and adjuvant endocrine therapy (p=0.017), respectively. SNPs in AQP5 are not associated with hematogenous or lymphogenous tumor cell spread. However, we observed for the first time an association between SNPs in AQP5 and progesterone receptor positivity, which might have implications for future adjuvant treatment. Further investigations must include more than one AQP as well as factors promoting angiogenesis to elucidate the different modes of tumor cell dissemination.

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