Haploinsufficiency of 8p22 may influence cancer-specific survival in prostate cancer

Although Knudsonʹs two-hit hypothesis with functional loss of a tumor suppressor gene has been widely accepted, accumulating evidence suggests that several genes are regulated by the quantity of their product in a dose-dependent manner (gene dosage effect). The study was designed to identify the influence of gene dosage effect of 8p22 on patient prognosis. With a median age of 71 years, 40 patients with prostate cancer (11 organ-confined, 13 capsular penetrating, and 16 nodal and/or distant metastatic) were followed for a median of 68.5 months. A fluorescence in situ hybridization (FISH) technique was applied using a region-specific cosmid probe combined with centromeric probe. Allelic losses of 8p22, 8p21.3, 8p21.1∼2, and 8p12 were found in 23, 22, 14, and 9 patients, respectively. A Cox proportional hazard model revealed that decreased fraction (i.e., the fraction of nuclei with a lesser number of cosmid signals than of centromeric probe signals) of 8p22 proved to be the sole independent prognostic factor predicting cancer-specific death, as well as disease progression—but allelic loss of 8p22 was not predictive. Cytogenetic estimation of 8p22 by FISH can yield quantitative evaluation of relevant gene dosage, which may become a useful biomolecular marker predicting poor patient prognosis.