The act of observation can affect the apparent incidence of cancer, as well as the apparent risk factors for the disease. The ideas and opinions piece from H. Gilbert Welch, MD, MPH, of The Dartmouth Institute for Health Policy and Clinical Practice and Otis Brawley, MD, FACP, of the American Cancer Society, is published in Annals of Internal Medicine.
‘Income and education are not the major risk factors for breast cancer. However, they are more likely to be the risk factors for screening cancer.’
The authors point to prostate cancer as an example of scrutiny-dependent cancer. When physicians look harder for it, more cases become apparent; when they look less hard, fewer cases become apparent. Indolent prostate cancer is common, which means increased detection is likely to be overdiagnosis.
Indolent thyroid cancer, melanoma, and breast cancer are also scrutiny-dependent cancers, according to the authors; and the degree of scrutiny can also affect the assessment of risk factors. For example, The more scrutiny, the more likely that biologically indolent (low grade) cases of breast cancer are found.
Relative to cancer found by women themselves, cases found by mammography, ultrasound, or MRI are more likely to be indolent. As physicians look harder, they find not only more cases of cancer, but those that are less important, or more likely to grow slowly.
This same scrutiny affects assessment of risk factors. Recent data shows that women in the highest quintile of neighborhood socioeconomic status had twice the rate of breast cancer diagnosis as women in the lowest quintile.
High socioeconomic status is not likely a true independent risk factor for breast cancer. Instead, women in these neighbrohoods are more connected to health care and more likely to undergo not just mammography, but ultrasound and MRI, as well.
The authors conclude that risk factor epidemiology must shift from diagnosis to "harder" outcomes more related to the disease process.
As cancer diagnosis becomes increasingly sensitive to scrutiny, those investigating the risk for cancer should focus on risk factors for death from cancer, and not just the cancer diagnosis.