Though prostate cancer is often indolent, it is nonetheless a leading cause of 
cancer death. Defining the underlying molecular genetic alterations may lead to 
new strategies for prevention or treatment. Towards this goal, we performed 
array-based comparative genomic hybridization (CGH) on 86 primary prostate 
tumors. Among the most frequent alterations not associated with a known cancer 
gene, we identified focal deletions within 5q21 in 15 out of 86 (17%) cases. By 
high-resolution tiling array CGH, the smallest common deletion targeted just one 
gene, the chromatin remodeler chromodomain helicase DNA-binding protein 1 
(CHD1). Expression of CHD1 was significantly reduced in tumors with deletion 
(P=0.03), and compared with normal prostate (P=0.04). Exon sequencing analysis 
also uncovered nonsynonymous mutations in 1 out of 7 (14%) cell lines (LAPC4) 
and in 1 out of 24 (4%) prostate tumors surveyed. RNA interference-mediated 
knockdown of CHD1 in two nontumorigenic prostate epithelial cell lines, OPCN2 
and RWPE-1, did not alter cell growth, but promoted cell invasiveness, and in 
OPCN2-enhanced cell clonogenicity. Taken together, our findings suggest that 
CHD1 deletion may underlie cell invasiveness in a subset of prostate cancers, 
and indicate a possible novel role of altered chromatin remodeling in prostate 
tumorigenesis.