Questioning the benefits of current screening protocols for common cancers

Abstract

Screening is the application of a diagnostic test to a population of patients without suspicious clinical signs or symptoms of a disease. Applying screening protocols to detect cancer is especially attractive as cancer is a growing burden and earlier detection of malignancies can lead to better outcomes. While the initial excitement over screening for cancers has caused protocols to be put into practice, data analysis has cast doubt on the net benefit. Prostate-specific antigen (PSA) blood testing has been used as a screening test for prostate cancer. The harms of a positive PSA screen include invasive investigations and treatments with side effects such as infection and incontinence. The poor sensitivity and specificity of PSA screening caused the Canadian Task Force on Preventive Health Care to recommend against PSA as a screening tool. Similarly, mammography and ultrasound for detecting breast cancer lesions in asymptomatic women suffer from relatively low sensitivity and specificity. The harms of screening include emotional stress and invasive surgical procedures. Meta-analyses reveal that the risks outweigh the benefits for some age groups, but there may be a role in screening asymptomatic patients with a family history of breast cancer with more sensitive but more expensive modalities, such as magnetic resonance imaging (MRI). Finally, colonoscopy, which is the gold standard to diagnose colorectal cancers, has failed to show net benefit in screening. While screening protocols thus far have provided underwhelming results, the key in screening in the future may lie in using tests with high specificity and sensitivity, as in next generation screening modalities that rely on molecular markers and analytics.