Loss of heterozygosity (LOH) involving the long arm of chromosome 13 has been reported to occur in as many as one third of primary prostate cancers. Candidate tumor suppressor genes on 13q that may be important in the development of prostate cancer include the retinoblastoma susceptibility gene (RB1) and a gene associated with inherited breast cancer (BRCA2). To define the pattern of allelic loss of 13q in prostate cancer, LOH analysis was performed using nine mapped polymorphic markers spanning the entire chromosomal arm. Nineteen (48%) of 40 prostate cancer cases obtained following radical prostatectomy demonstrated allelic loss with at least one marker. Furthermore, 13 (33%) of 40 cases had evidence of allelic loss involving a region of 13q14 containing RB1. To test the hypothesis that RB1 is the targeted tumor suppressor gene in this region, 37 of 40 cases were assessed for expression of pRB, the protein product of RB1 using immunohistochemical techniques. By this analysis, 8 (22%) of 37 prostate tumors demonstrated no pRB expression. However, allelic loss at RB1, assessed with an intragenic marker, did not correlate with absent pRB expression (Fisher's exact test, P = 0.375). Taken together, these data confirm that allelic loss of a common region of 13q14 occurs in approximately one third of prostate cancers. Lack of correlation of LOH at RB1 with absent pRB expression suggests the existence of another tumor suppressor gene in this region important in prostate cancer.

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Supported in part by a grant from the John and Suzanne Munn Endowed Research Fund of the University of Michigan Comprehensive Cancer Center (K. A. C.), by NIH Grant KO8 HL02839 (K. A. C.), by NIH Grant 3MO11RR00042-3451 (S. D. M.), by NIH Grant R29CA60948 (J. A. M.), by the Department of Veterans Affairs (J. A. M.), and by NIH Grant P50 CA69568.

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