c-kit and SCF expression in normal and tumor breast tissue

Several studies have shown a role of the tyrosine kinase receptor, c-kit, and its ligand, SCF, during organogenesis, normal cell development and growth of some tumor histotypes. In breast cancer, studies using different methodologies have shown conflicting results. In the present study we analyzed c-kit and SCF in 14 normal mammary epithelia samples, in 16 in situ and in 75 invasive breast cancers. The expression of c-kit and SCF protein was analyzed by immunohistochemistry and mRNA expression was evaluated by in situ hybridization and reverse-transcriptase polymerase chain reaction (RT-PCR). The different methodologies gave somewhat different results. Using immunohistochemistry and in situ hybridization, protein and mRNA expression of c-kit and SCF were high in normal mammary gland, significantly lower in in situ and almost completely undetectable in invasive breast cancer. Conversely, using RT-PCR, mRNA expression was observed in normal tissue and in all pathologic lesions of mammary gland, probably due to the high sensitivity of the methodology or to the positivity of elements other than tumor cells expressing the receptor and/or its ligand. These results suggest that the c-kit/SCF pathway plays an important role in the maintenance of normal growth of mammary epithelium and that the process of malignant transformation is accompanied by their progressive loss. Furthermore, we demonstrated that different results are attributable to different methodologies and that morphologic approaches are the most reliable for defining the cellular source of c-kit or SCF expression.