Identification of Pathogenic Mechanisms in Sebaceous Carcinoma by Gene Expression Analysis

Abstract

Purpose:: Sebaceous carcinoma is a malignant neoplasm that arises from the Meibomian glands, the glands of Zeis, and the sebaceous glands of the caruncle. Treatment options for more advanced sebaceous carcinoma generally result in limited success, in part because the tumor is typically highly resistant to topical chemotherapy and radiation. No reports to date have analyzed global gene expression patterns in sebaceous carcinomas. The objective of this study was to define the gene expression profile for sebaceous carcinoma tissue compared to matched control tissue in order to identify potential targets for therapy.

Methods:: Paraffin-embedded tumor specimens of patients previously diagnosed with sebaceous carcinoma were obtained from tissue blocks. Tumor tissue was deparaffinized and total RNA was isolated. Spectrophotometry was used to assess purity and amount of RNA obtained. Expression of a panel of known tumor suppressor genes in both sebaceous carcinoma tissue and control tissue was examined using reverse transcriptase polymerase chain reaction (rtPCR). Expression of genes encoding for ligands that stimulate the Wnt pathway and the RAS pathway were examined.

Results:: Spectrophotometry demonstrated that the median A260/280 for paraffin-embedded control tissue (fibrovascular stroma adjacent to tumor) and sebaceous carcinoma, respectively, were 2.2 and 1.67 (n=8). This finding indicates that pure RNA from tumor tissue and stroma was able to be consistently isolated from lid specimens that had been embedded in paraffin for years. The two genes found to be most consistently expressed in the tumor tissue but not in the control tissue were survivin1 and Wnt11.

Conclusions:: Survivin1 and Wnt11 were over-expressed in sebaceous carcinoma tissues compared to matched control tissue samples, suggesting a role for the Wnt pathway in tumorigenesis of this cancer. We are currently also identifying gene expression changes using microarrays which will extend these findings and help to create distinct molecular profiles correlated with prognosis. The identification of these genes will offer insight into sebaceous carcinoma pathogenesis and will provide a practical foundation for the future development of targeted drug therapy.

Keywords: tumors • eyelid • gene/expression