Controversies in Cancer Screening: Focusing on Colorectal Cancer Recommendations

Abstract

Screening recommendations for common malignancies, such as cervical, breast, and prostate cancer, have been ques­ tioned in the past year, and vigorous professional, public, and private debates have ensued. For breast cancer screen­ ing, mammography recommendations have been rethought, most notably by the U.S. Preventive Services Task Force. Their recommendations support the use of mammography, but changes have been suggested regarding the ages to begin and end screening, as well as the frequency of the screening studies. Whereas for breast cancer very few have questioned a benefit of mammography in the appropriate population and situation (however, for opposing viewpoints, see Zahl et al), the case is different regarding prostate cancer screen­ ing. The use of prostate­specific antigen as a screening tool has been studied and found to be of questionable benefit. In certain clinical situations it might even lead to more harm than benefit. A fourth group of malignancies for which scree­ ning procedures are commonly used is colorectal cancers. Most physicians consider that colorectal cancer screening is beneficial and underutilized. Recent articles have discussed this underutilization, but have also noted that in various clinical scenarios, there is, surprisingly, inappropriate and over utilization, particularly regarding colonoscopies. For instance, the U.S. Preventive Services Task Force has issued guidelines for appropriate follow­up colonoscopic surveil­ lance after initial colonoscopy, including addressing when the initial exam reveals polyps. Despite these guidelines, it is common clinical practice to perform follow­up colonos­ copies more frequently and at shorter intervals than those recommended by expert committees. The controversies over breast and prostate cancer screen­ ings have highlighted a paradox: Inappropriate and overuse of screening tests can lead to adverse consequences, as well as incurring significant financial costs (thereby reducing financial resources that can be used for other important medical needs). Far beyond patients experiencing anxiety due to a large number of false positive screening studies, patients undergo considerable noninvasive and invasive testing, and a substantial number of patients are even treated for malignancies that would never impact on the quality or length of their lives. This unnecessary treatment scenario is widely recognized with prostate cancer, where patients undergo major procedures, not infrequently leading to incontinence and sexual dysfunction, for malignancies that would never progress in their lifetime. This is also true, though not as well known, for breast cancer. It is commonly known, exp­ ected and accepted that a percentage of patients will have an abnormal mammogram that will lead to further proce­ dures, including biopsies, which will ultimately rule out an invasive malignancy. Though this is known, it is enlighten­ ing to appreciate the frequency with which this occurs. Varying slightly with the age of the woman, if 1000 women were screened biennially for 10 years, approximately 200 will have an abnormal mammogram, and 60 will eventually have a biopsy. What isn’t as well known is that beyond the diagnosis and recognized conundrum of ductal carcinoma in situ, a clinical situation that will not progress to invasive breast cancer in most women, there is also a substantial overdiagnosis of invasive breast cancer, which then leads to treatment, including some combination of breast sur­ gery, radiation therapy, chemotherapy, and hormonal therapy. Though it seems counterintuitive and far beyond what one would expect, this overdiagnosis and subsequent treatment has been calculated to be as high as 30% to 40% of all the invasive breast cancers diagnosed. Balancing these nega­ tive consequences of screening mammography, it is esti mated that the number of lives saved for every 1000 women screened for 10 years is (age 40­50 years) 0.5 women, (age 50­60 years) 2 women, (age 60­70 years) 3 women, (age 70­80 years) 2 women. Screening controversies have arisen primarily due to the natural biological processes of these malignancies, which were not well appreciated until recently. Screening, as presently practiced, is based on the assumption that tumors, when small, are localized, and that if they are not removed while still small, they eventually grow and metastasize. Therefore, it is postulated that if they are discovered early, this metastatic spread can be prevented. However, it has become clear that not only do some tumors,