PURPOSE: Familial ovarian cancer is most often associated with hereditary breast 
and ovarian cancer, implicating mutations in the BRCA1 and BRCA2 genes. 
Hereditary nonpolyposis colorectal cancer, another common syndrome, is also 
associated with ovarian cancer and is caused by DNA mismatch repair genes. We 
sought to identify the role of hereditary nonpolyposis colorectal cancer in 
women with family histories of ovarian cancer.
METHODS: The likelihood of a genetic syndrome in 226 oophorectomized women in 
the Gilda Radner Familial Ovarian Cancer Registry was determined by pedigree 
analysis using clinical criteria and by calculating the probability of a 
mutation in genes responsible for hereditary breast and ovarian cancer and 
hereditary nonpolyposis colorectal cancer using available risk models.
RESULTS: Some 86% had a BRCA gene mutation likelihood of 7.8% or higher, 
warranting consideration of hereditary breast and ovarian cancer. Of the 32 
women below this threshold, 4 (12.5%) had family histories that met criteria for 
clinical diagnosis of hereditary nonpolyposis colorectal cancer. In addition, 16 
women (7%) with a BRCA mutation likelihood greater than 7.8% met clinical 
criteria for hereditary nonpolyposis colorectal cancer or warranted its 
inclusion in the differential diagnosis. Among all study respondents, 9% had 
family histories warranting consideration of hereditary nonpolyposis colorectal 
cancer.
CONCLUSION: Hereditary nonpolyposis colorectal cancer should be considered in 
the differential diagnosis of women with family histories of ovarian cancer.