Study of the association between estrogen receptor alpha gene expression in the levels of RNA and protein in primary breast tumors

Estrogen receptor alpha protein status is determined by routine immunohistochemistry analysis in all malignant breast tumors. This assay has its limitations. RNA based techniques are potential complements for immunohistochemistry but it must be noticed that gene silencing may occur at different levels from RNA to protein. The aim of this study was the comparison of the results from these two assays and characterizing the tumors subgroup in which gene expression occurs at RNA level but the target protein is absent. 92 primary breast tumors including their clinical and IHC results were collected before treatment. Estrogen receptor gene expression of tumors was studied by Reverse Transcription Polymerase Chain Reaction (RT PCR). In this assay, GAPDH was used as a reference gene. 36.6 % of tumors with negative estrogen receptor protein showed gene expression at mRNA level. In this subgroup most of the patient were older than 50 years and in stages 3 or 4 of breast cancer and had poor prognosis according to Nottingham prognostic index. Most cases of the perineural invasion have been seen in this subgroup. It seems that RT-PCR assay would enable us to recognize a subgroup of breast tumors with poor prognosis which expresses RNA but not protein.