Aneuploidy of chromosome 9 and the tumor suppressor genes p16(INK4) and p15(INK4B) detected by in situ hybridization in locally advanced prostate cancer

Introduction and Objectives: The linked p16(INK4)/MTS1 and p15(INK4B)/MTS2 genes on chromosome 9p21 encode proteins that inhibit the cyclinD dependent kinases CDK4/6. Biallelic homozygous deletions involving this locus have b een identified in a wide range of tumor cell lines, but in a lower frequenc y of primary tumors. As PCR based approaches analyzing for homozygous delet ions could be confounded by unavoidable contributions of normal cells in mi crodissected tissue, we performed in situ hybridization (ISH) on primary pr ostate carcinomas to accurately evaluate p16 and p15 copy numbers on a cell -by-cell basis. Material and Methods: p16 and p15 loci were evaluated in 28 pT3N0M0 prostat e cancer specimens. Of 28 patients, 15 (53%) were ascertained showing no re currence (mean follow-up 61+/-17 months), 13 (47%) developed recurrences wi thin 27+/-19 months. Tissues were provided for ISH analysis in a blinded fa shion. Isolated DNA derived from P1 clone 1063 compromising p16 and p15 as well as a centromeric probe for chromosome 9 were used for hybridization. S ignals were enumerated within 300 interphase nuclei per tumor specimen, and in 100 nuclei derived from 18 benign prostate tissues and 7 adjacent PIN r egions. Results: ISH detected aneuploid tumors in 12/13 (92%) patients with recurre nce and in 5/15 (33%) without recurrence (p<0.0014). Whereas 3/7 PIN specim ens associated with nonrecurrent PCA demonstrated euploidy, all 4/7 PIN ass ociated with recurrent disease demonstrated the same aneuploidy for chr9 as the primary tumor. All benign tissues evaluated exhibited euploidy for chr 9, p16 and p15. None of the PCA and PIN samples revealed homozygous deletio ns for p16(INK4)/MTS1/p15(INK4B)/MTS2; 2/28 (7.1%) PCA exhibited partial de letion for p16(INK4)/MTS1/p15(INK4B)/MTS2 and aneuploidy for chr9; both PCA derived from the recurrent group. Conclusions: Deletion of 9p21 was rare and therefore such genetic alteratio ns may not play an important role in the pathogenesis of PCA. Analysis of t he limited number of PCA examined suggest a strong association between chr9 aneuploidy and recurrenct disease. Aneuploidy in both PIN and PCA suggests that the clinical outcome of PCA might already be determined in the preinv asive PIN. Copyright (C) 2000 S. Karger AG, Basel.