Quantification of insulin receptor mRNA splice variants as a diagnostic tumor marker in breast cancer

BACKGROUND: The mature human insulin receptor (INSR) has two isoforms: The A isoform and the B isoform. INSR upregulation has been suggested to play a role in cancer. OBJECTIVE: To establish quantitative PCR method for INSR transcript variants and examine their differential expression as a diagnostic tumor marker in breast cancer. METHODS: The differential expression of IR-A and IR-B were evaluated by TaqMan qRT-PCR assay in the commercially available Breast Cancer Disease cDNA and Cancer Survey cDNA arrays. RESULTS: The mRNA expression levels of IR-A was statistically significantly higher in breast cancer when compared to normal breast tissue while IR-B mRNA expression was down regulated significantly in breast cancer. Stratification of patients into groups according to metastatic stages indicated statistically significantly higher levels of IR-A mRNA in clinical stage (CS)-IV, and lower IR-B levels in CS-IIA, CS-IIIB and CS-IIIC. However, IR-A:IR-B ratio showed a statistically significant increase in all stages. Cancer Survey cDNA array demonstrated lower levels of IR-B mRNA in breast adenocarcinoma, liver carcinoma and lung carcinoma only while IR-A expression was significantly altered in kidney carcinoma without any significant differences in IR-A:IR-B ratios. CONCLUSIONS: The results demonstrate an increased IR-A:IR-B ratio in all clinical stages of breast cancer. Thus, IR-A:IR-B ratio may have a diagnostic biomarker utility in breast cancer.