Background: The role of mutations in protooncogenes and their regulatory sequences in the pathogenesis of cancer is under close scrutiny. Minisatellites are unstable repetitive sequences of DNA that are present throughout the human genome. The highly polymorphic HRAS1 minisatellite locus just downstream from the protooncogene H-ras-1 consists of four common progenitor alleles and several dozen rare alleles, which apparently derive from mutations of the progenitors. We previously observed an association of the rare mutant alleles with many forms of cancer, and we undertook the present study to pursue this observation further.
Methods: We conducted a case-control study, typing 736 HRAS1 alleles from patients with cancer and 652 from controls by Southern blotting of leukocyte DNA. We also carried out a meta-analysis of this study and 22 other published studies, estimating the relative risk of cancer (such as bladder, breast, or colorectal cancer) when one of the rare HRAS1 alleles was present.
Results: Both the present case-control study (odds ratio, 1.83; 95 percent confidence interval, 1.28 to 2.67; P = 0.002) and the present study combined with our previous study (odds ratio, 2.07; 95 percent confidence interval, 1.47 to 2.92; P < 0.001), as well as the meta-analysis of all 23 studies (odds ratio, 1.93; 95 percent confidence interval, 1.63 to 2.30; chi-square = 57.58; P < 0.001), replicated our original finding and demonstrated a significant association of rare HRAS1 alleles with cancer. We found significant associations for four types of cancer: carcinomas of the breast, colorectum, and urinary bladder and acute leukemia. We also identified suggestive but not statistically significant associations for cancers of the lung and prostate and for non-Hodgkin's lymphoma.
Conclusions: Mutant alleles of the HRAS1 minisatellite locus represent a major risk factor for common types of cancer. Although the relative risk associated with the presence of one rare allele is moderate, the aggregate prevalence of one rare allele is moderate, the aggregate prevalence of this class of mutant alleles implies an extremely important attributable risk: 1 in 11 cancers of the breast, colorectum, and bladder.