Familial Cancer Risk Overestimated
Is it really always genes or environmental influences that are responsible for increased incidences of cancer cases in individual families? Dr. Justo Lorenzo Bermejo and Professor Dr. Kari Hemminki of the German Cancer Research Center (Deutsches Krebsforschungszentrum, DKFZ) have identified and drawn attention to a reason why cancer incidence in some families is above average. The authors assume that, concerned about a cancer diagnosis of a close relative, the children or siblings of the affected are more likely to take advantage of early detection examinations. Thus, more tumors are diagnosed in an early stage, which might otherwise have gone undetected.
Based on data of the Swedish Family Cancer Register, the epidemiologists have studied the occurrence of cancer in nearly 1.7 million offspring and siblings of about 850,000 cancer patients and compared it to the general population of Sweden. The researchers studied cases of breast, colorectal, lung, cervical and prostate cancers as well as melanomas.
The epidemiologists argue that if individual health concerns do really play a role, then the number of cancers diagnosed in relatives of a cancer patient should be particularly high in the year of the first cancer diagnosis in the family. In the following years, this increased familial incidence should disappear.
This interrelation turned out to be clearly noticeable in daughters of breast cancer patients: In the year of the mother’s diagnosis, they were diagnosed with locally confined breast cancer 4.78 times more often than the general population, while five years later hardly any increase in familial incidence was observed. If a parent was diagnosed with melanoma, this type of skin cancer was diagnosed in the same year in his or her offspring eight times more often than in the general population.
In siblings of cancer patients the risk of locally confined breast or cervical cancers as well as prostate cancer also decreased with the years following the sibling’s diagnosis.
“Our data clearly show that cancer of a close relative artificially increases familial cancer risk”, concluded Kari Hemminki. “This effect must be taken into account in medical counseling about familial cancer risks so as not to cause unnecessary anxiety in advice seekers.”
Justo Lorenzo Bermejo, Kari Hemminki: Familial Risk of Cancer Shortly After Diagnosis of the First Familial Tumor. Journal of the National Cancer Institute, 97(21):1-5, 2005
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