Editor—The main purpose of offering predictive genetic testing for hereditary cancer is to reduce unnecessary worry among those with a low risk of cancer (mutation negative) and to recognise those with a high risk (mutation positive), so as to promote preventive measures.1 2 Ideally, those shown to be at high risk would understand this, would learn to live with the knowledge, and, most importantly, would attend cancer surveillance programmes regularly. Those at low risk would feel relieved and no physically and emotionally uncomfortable surveillance would be needed. This result would be seriously hampered if those tested did not fully understand the meaning of the test results, which could lead to unnecessary worry or failure to adhere to surveillance. At present, most predictive tests are performed in carefully organised settings, which include comprehensive pre- and post-test counselling that would be expected to minimise the risk of misunderstanding the test result. However, commercial tests predicting cancer are already available,3 and this has raised concerns about predictive testing with minimal counselling or even without personal contact with a health care professional.1 4

The impact of genetic counselling on risk perception and impact of risk perception on genetic testing intentions has been studied previously.5 However, this is the first report on the comprehension of test results (perception of cancer risk) after predictive genetic testing for cancer, in this case hereditary non-polyposis colorectal cancer (HNPCC), which is the most common form of hereditary colon cancer. HNPCC is an autosomal dominant disease of adulthood with an 80-90% lifetime risk for colorectal cancer and a lesser risk of extracolonic cancers, the most common of which are endometrial and gastric cancer.6 Hereditary colorectal cancer differs essentially from other hereditary cancers, of which hereditary breast cancer is a good example. Firstly, in …