Purpose: Our laboratory has recently identified a 1 to 2 Mb homozygous deletion at 12p12-13 in a prostate cancer specimen and determined that the p27/kip1 gene lies within the deletion. While immunohistochemical analysis has implicated p27/kip1 in prostate carcinoma, no previous studies had identified genetic abnormalities at this locus. Here, we examined primary and metastatic prostate tumors to determine if allelic loss occurs at this locus in localized disease and if it increases the risk of metastatic, high stage or high-grade disease.
Materials and methods: DNA was extracted from prostate tumors and normal tissue of 99 patients. 60 tumors were primary, 20 were metastatic pelvic lymph nodes, and 19 were distant metastases. Multiple metastases were analyzed from 11 of 19 patients with metastatic disease. Polymorphic markers spanning our region of interest were PCR amplified from tumor and normal DNA. PCR products were then scored for allelic loss.
Results: Loss of heterozygosity (LOH) was identified in 14/60 (23%) primary tumors, 6/20 (30%) lymph node metastasis, and 9/19 (47%) distant metastases. The difference between primary and distant metastatic disease was statistically significant (p = 0.045, Fisher's exact test). The pattern of LOH was identical in all metastatic sites obtained from individual patients, indicating that genetic loss occurred prior to metastasis. Subset analysis of the 60 primary tumors demonstrated no association between LOH and adverse pathological feature [nodal involvement, seminal vesicle invasion, margin positivity, high Gleason score (7-10)].
Conclusions: Demonstrating that 12p12-13 LOH is a prominent feature of primary prostate tumors and that multiple metastatic foci have an identical LOH pattern, provides evidence that gene inactivation in this region occurs prior to metastasis. In addition, the strong association between LOH and distant metastasis raises the possibility that mutational inactivation of a gene at 12p12-13, possibly p27/kip1, plays a pivotal role in the development of metastatic disease.