Expression of Retinoblastoma Protein in Cutaneous Squamous Cell Carcinomas and Basal Cell Carcinomas

ABSTRACT

There is increasing evidence that inactivation of tumor-suppressor genes can promote tumor growth. Retinoblastoma protein (pRb) is the product of the retinoblastoma gene located on chromosome 13q14. pRb negatively regulates cell growth when functioning normally. Mutational inactivation of the Rb gene has been observed in retinoblastomas, osteosarcomas and soft tissue sarcomas. Recently, several other human cancers have also been shown to carry abnormalities of the Rb gene. The potential role of the Rb gene in cutaneous squamous cell carcinomas (SCCs) and basal cell caicinomas (BCCs), has not been determined and was the focus of this study. Immunohistochemical expression of pRb in 16 cutaneous SCCs and 17 BCCs was examined. The expression of PCNA was studied in parallel to assess the cellular proliferation rate in these lesions. The pRb and PCNA immunoreactivity were localized to the nuclei of tumor cells. A few pRb and PCNA positive cells were seen in normal squamous epithelium, sebaceous glands, sweat glands and hair follicles. The loss of expression of pRb was seen in 3 of 16 SCCs(18.8%) and 6 of 17 BCCs (35.3%). PCNA immunoreactivity was slightly high in pRb-negative or lower-positive cases. PCNA immunoreactivity was similar to that produced by pRb in some cases. These results suggest that mutational inactivation of the Rb gene may be related to the carcinogenesis of cutaneous SCC and BCC, though the frequency is relatively low.