THE USE AND INTERPRETATION OF COMMERCIAL APC GENE TESTING FOR FAMILIAL ADENOMATOUS POLYPOSIS

Background The use of commercially available tests for genes linked to familial cancer has aroused concern about the impact of these tests o n patients. Familial adenomatous polyposis is an autosomal dominant di sease caused by a germ-line mutation of the adenomatous polyposis coli (APC) gene that causes colorectal cancer if prophylactic colectomy is not performed. We evaluated the clinical use of commercial APC gene t esting. Methods We assessed indications for APC gene testing, whether informed consent was obtained and genetic counseling was offered befor e testing, and the interpretation of the results through telephone int erviews with physicians and genetic counselors in a nationwide sample of 177 patients from 125 families who underwent testing during 1995. R esults Of the 177 patients tested, 83.0 percent had clinical features of familial adenomatous polyposis or were at risk for the disease - bo th valid indications for being tested. The appropriate strategy for pr esymptomatic testing was used in 79.4 percent (50 of 63 patients). Onl y 18.6 percent (33 of 177) received genetic counseling before the test , and only 16.9 percent (28 of 166) provided written informed consent. In 31.6 percent of the cases the physicians misinterpreted the test r esults. Among the patients with unconventional indications for testing , the rate of positive results was only 2.3 percent (1 of 44). Conclus ions Patients who underwent genetic tests for familiar adenomatous pol yposis often received inadequate counseling and would have been given incorrectly interpreted results. Physicians should be prepared to offe r genetic counseling if they order genetic tests. (C) 1997, Massachuse tts Medical Society.