Is the phenotype mixed or mistaken? Hereditary nonpolyposis colorectal cancer and hyperplastic polyposis syndrome.

PURPOSE: Hereditary nonpolyposis colorectal cancer is a hereditary syndrome defined by personal and family history of colorectal and other cancers. Some patients with this condition have multiple serrated polyps, which are the hallmark of hyperplastic polyposis syndrome, a rare colorectal cancer syndrome characterized by multiple hyperplastic/serrated polyps and an increased risk of colorectal cancer. We hypothesized that this may represent a unique group of patients, and this study investigates a possible association between the two syndromes.
METHODS: A hereditary colorectal cancer registry was reviewed for patients who fit hereditary nonpolyposis colorectal cancer or familial colorectal cancer and hyperplastic polyposis syndrome criteria.
RESULTS: Twelve patients from seven families were identified. Four families had more than one person meeting the criteria. All patients were white, and four were women. Ten of 12 patients fit Amsterdam criteria, and two were designated with familial colorectal cancer. The median cumulative number of hyperplastic polyps resected per patient was 6, half of which were located in the right colon. Seven of the 12 patients developed colorectal cancer. Ten patients had personal or family history of other cancers: prostate, breast, testicular, salivary gland, lung, and Hodgkin's disease.
CONCLUSIONS: Patients meeting criteria for hereditary nonpolyposis colorectal cancer may also carry a diagnosis of hyperplastic polyposis syndrome. Possible explanations include: 1) two hereditary syndromes are present in the same patient, 2) serrated polyps are part of the phenotype of hereditary nonpolyposis colorectal cancer, or 3) hereditary nonpolyposis colorectal cancer is potentially misdiagnosed in some families who do, in fact, have hyperplastic polyposis.