Accurate assessments of the risk of cancer among the family members of cancer patients are essential for clinical and genetic counseling. Knowledge of these risks may also help to identify environmental and/or heritable factors that are associated with the risks of specific cancers and may lead to prevention strategies. Because a person's diagnosis of cancer may trigger the medical examination of their relatives and the subsequent identification of more cancers, detection bias may be present and the familial risks of cancer may therfore be overestimated.
Justo Lorenzo Bermejo, Ph.D., of the German Cancer Research Centre in Heidelberg, and Kari Hemminki, M.D., Ph.D., of the German Cancer Research Centre and the Karolinska Institute in Huddinge, Sweden, followed nearly 1.7 million offspring and siblings of almost 850,000 people who had been diagnosed with cancer. They compared the incidence of melanoma and cancers of the breast, cervix, colon/rectum, lung, and prostate among relatives of patients with the incidence of those cancers in the general population.
The researchers found that daughters of women with breast cancer were more likely to be diagnosed with in situ breast cancer during the year following their mother's diagnosis than they were 5 or more years later. Similarly, the offspring of people diagnosed with melanoma were more likely to be diagnosed with melanoma in the year following their parent's diagnosis than they were 5 or more years later. In addition, the risks of in situ breast cancer, in situ cervical cancer, and invasive prostate cancer in siblings decreased with time after the diagnosis of the first familial tumor.
"The most likely reason for the detection of familial cancers close in time is that the first diagnosis leads to the earlier detection of some asymptomatic tumors by increased surveillance in relatives," the authors write.
In an editorial, Marvin Zelen, Ph.D., of the Harvard School of Public Health in Boston, notes that data on familial cancer risks may also be influenced by fluctuations in family size and that controlling for this may lead to more precise analyses. "It is apparent that in counseling, care must be taken with respect to using cancer risks derived from observations on families," he writes.
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