5q21 deletion is often heterogeneous in prostate cancer.

Cancer heterogeneity represents a challenge for the analysis of prognostic molecular markers but can be used to study the evolution of molecular events in tumors. To assess the degree of heterogeneity of 5q21 deletions and their relationship with TMPRSS2:ERG status and 6q15 deletions in prostate cancer, a heterogeneity tissue microarray including 10 tissue spots from 10 different areas of 317 cancers was analyzed by fluorescence in situ hybridization for 5q21 deletion. Data on 6q and ERG were available from earlier studies. Deletions of 5q21 were found in 23% of 265 interpretable cancers and showed marked intratumoral heterogeneity. In the subset of 246 cancers with at least 3 interpretable spots, 23% had a 5q21 deletion. Heterogeneous 5q21 deletions were found in 71% and homogeneous in 29% of these cancers. The likelihood of 5q21 deletion was twice as high in ERG-negative (28%) than in ERG-positive cancers (16%, P = .024). In all 21 cases harboring both alterations, the tumor area containing a 5q21 deletion was smaller or equally large than the ERG-positive area but never larger. Deletions of 5q and 6q were significantly linked. However, the analysis of 32 tumors harboring both deletions did not suggest a specific order of appearance of these deletions. The 5q21 deletion preceded 6q15 in 10 tumors and 6q15 preceded 5q21 in 14 tumors. In summary, our study identifies 5q21 deletion as a highly heterogeneous aberration in prostate cancer that usually occurs late during cancer progression. This is a severe limitation for using 5q21 testing as a prognostic tool.

p16 overexpression and 9p21 deletion are linked to unfavorable tumor phenotype in breast cancer.

Overexpression of the p16 tumor suppressor, but also deletion of its gene locus 9p21, is linked to unfavorable tumor phenotype and poor prognosis in breast cancer. To better understand these contradictory observations, and to clarify the prognostic impact of p16 expression and 9p21 deletion, a tissue microarray (TMA) with 2,197 breast cancers was analyzed by fluorescence in-situ hybridization and immunohistochemistry (FISH) for 9p21 deletion and p16 expression. p16 immunostaining was weak in 25.6%, moderate in 7.1%, and strong in 12.7% of 1,684 evaluable cancers. Strong p16 staining was linked to advanced tumor stage (p = 0.0003), high-grade (p < 0.0001), high tumor cell proliferation (p < 0.0001), negative hormone receptor (ER/PR) status (p < 0.0001 each), and shorter overall survival (p = 0.0038). 9p21 deletion was found in 15.3% of 1,089 analyzable breast cancers, including 1.7% homozygous and 13.6% heterozygous deletions. 9p21 deletion was linked to adverse tumor features, including high-grade (p < 0.0001) and nodal positive cancers (p = 0.0063), high cell proliferation (p < 0.0001), negative hormone receptor (ER/PR) status (p ≤ 0.0006), and HER2 amplification (p = 0.0078). Patient outcome was worse in 9p21 deleted than in undeleted cancers (p = 0.0720). p16 expression was absent in cancers harboring homozygous 9p21 deletions, but no difference in p16 expression was found between cancers with (59.2% p16 positive) and without heterozygous 9p21 deletion (51.3% p16 positive, p = 0.0256). In summary, p16 expression is unrelated to partial 9p21 deletion, but both alterations are linked to aggressive breast cancer phenotype. High-level p16 expression is a strong predictor of unfavorable disease course in breast cancer.