A REGION OF HOMOZYGOUS DELETION ON CHROMOSOME 9P21-22 IN PRIMARY NASOPHARYNGEAL CARCINOMA

Using 21 microsatellite polymorphic markers spanning both p and q arms , we have performed detailed deletion mapping on chromosome 9 in 18 pr imary nasopharyngeal carcinomas. All 18 tumors were informative at mul tiple loci. Eleven of the 18 cases (61%) demonstrated allelic deletion of chromosome 9. Among these 11, 6 cases are likely to be tumors with monosomy of chromosome 9. The other 5 cases demonstrated partial dele tion by showing multiple areas of allelic loss. In one of the 5 cases, a homozygous deletion region was identified which includes D9S126, D9 S171, and IFNA loci at 9p21-22, situated between loci D9S161 (9p21) an d D9S162 (9p21-22). The presence of a homozygous deletion strongly sug gests the presence of tumor suppressor gene(s) involved in the tumorig enesis of nasopharyngeal carcinoma. The same region has been reported to include some potential tumor suppressor gene loci in other cancers. This is the first reported finding of frequent genetic loss observed on chromosome 9 in nasopharyngeal carcinomas in addition to allelic lo ss on chromosome 3p at specific regions. Our results suggest that tumo rigenesis and progression of nasopharyngeal carcinomas, like other sol id tumors, involves multiple genetic changes associated with the inact ivation of tumor suppressor genes.