Overexpression of sphingosine kinase 1 is predictive of poor prognosis in human breast cancer

Sphingosine kinase 1 (SPHK1) is a bioactive lipid mediator that has been identified as a biomarker in various cancers and is considered to play an important role in tumor progression. In the present study, the expression level of SPHK1 was examined in breast cancer clinical specimens, and its association with patient survival was investigated to clarify the clinical significance of SPHK1 in breast cancer. SPHK1 mRNA expression was increased in breast cancer tissues compared with that in matched adjacent breast tissues in 19 of 32 paired tissue specimens (59.4%). Immunohistochemical analysis of 122 breast cancer cases revealed that the expression levels of SPHK1 were upregulated in 64 tumor tissues (52.5%), and increased expression levels of the protein were significantly associated with the presence of lymph node metastasis (P=0.0016), number of positive lymph nodes (P=0.0268) and presence of distant metastasis (P=0.0097). Increased SPHK1 protein expression was also associated with human epidermal growth factor receptor 2 status (P=0.0100), initial symptoms (P=0.0025) and tumor location (P=0.0457). Patients with increased SPHK1 protein expression had shorter overall survival and disease-free survival times compared with patients with lower SPHK1. Univariate and multivariate analyses indicated that high SPHK1 expression may be a poor prognostic factor. These results indicated that SPHK1 may perform an important role in breast cancer and may be a predictive factor in patients with breast cancer.