INFREQUENT INACTIVATION OF THE RETINOBLASTOMA GENE DESPITE FREQUENT LOSS OF CHROMOSOME 13Q IN HEAD AND NECK SQUAMOUS-CELL CARCINOMA

Our recent allelic analysis of head and neck squamous cell carcinomas identified a high incidence of chromosomal loss on 13q. To further def ine an area of minimal loss, we tested 60 primary head and neck squamo us cell carcinomas in 59 patients for loss of heterozygosity (LOH) by using 10 polymorphic microsatellite markers spanning the long arm of c hromosome 13. We examined the same primary tumors for inactivation of the retinoblastoma (Rb) gene by immunohistochemic al analysis of paraf fin-embedded specimens. Thirty-one of 60 (52%) tumors demonstrated LOH in at least one 13q marker. Twenty-nine of 31 (94%) lost a portion of 13q that included D13s133, which lies just telomeric to the Rb gene a t 13q14.3. However, immunohistochemical staining revealed absence of R b protein in only 6 of these 31 tumors (19.4%) with LOH. All but one t umor without LOH on 13q displayed normal Rb protein staining. Although Rb may be inactivated by an unusual mechanism in some head and neck s quamous cell carcinomas, our data suggest that another tumor suppresso r gene locus at 13q14 is likely to be involved in head and neck tumor progression.