Reference: JAMA Dermatol. 2023 Apr 18 early online
Practice Point: Keep doing skin checks for patients at high risk of skin cancer and of course biopsy those with suspicious lesions, but think twice before doing a whole body exam for asymptomatic people at average risk.
EBM Pearl: Don’t mistake an “insufficient” evidence rating from the USPSTF for there not being any data. Sometimes there is plenty of data but a lack of proven clinical benefit due to problems with data or conflicting evidence.
When an individual study fails to show a meaningful impact of an intervention, we often call the study “negative,” with the implication that the evidence is either a) sufficient and good enough quality to say that the intervention does not truly have an impact or b) the evidence isn’t strong enough to draw a conclusion. The United States Preventative Service Task Force recently reviewed the evidence on skin cancer screening and reaffirmed their “I” grade for insufficient evidence to recommend for or against this practice. How can this be? Skin cancer is very common, and although its most dangerous form (melanoma) represents only 1% of skin cancer, it accounts for the majority of skin cancer deaths and is usually recognizable when seen. Not only that, but the screening itself basically only requires a clinician to look at an unclothed patient, and diagnosis and treatment of early stage melanoma has a far better prognosis than metastatic disease.
So why isn’t screening for skin cancer a no-brainer? The Task Force lists several possible reasons for a recommendation to be given an “I” grade, including lack of evidence, poor quality evidence, and conflicting evidence. In this case, the “I” recommendation is related to conflicting evidence. When we think about conditions that are good candidates for screening, a “critical point” is necessary at which the condition (cancer) can be identified before symptoms present in time to make a difference in outcomes. Because melanoma is a fast-growing cancer, it may lack this critical point, leading to the possibility of an “interval” cancer that develops between screenings. These “interval” cancers were a significant factor in a nationwide screening campaign conducted by Germany in the early 2000’s which influenced the USPSTF’s “I” recommendation, wherein all Germans were eligible for a free total body skin exam conducted by trained clinicians every two years. During that program, which had almost 1 ½ million participants and lasted over six years, more skin cancers were detected in participants but skin cancer mortality did not go down. In fact, melanoma mortality rates rose faster than for other European countries during this time period. As it turned out, most of the melanomas detected in the screening group were found by patients themselves during the interval phase.
The German data could be interpreted as being inadequate - perhaps screening exams should be more frequent than every two years - but it also could be interpreted as evidence against one of our basic assumptions about screening for cancer: that early detection saves lives. There have been many ideas in medicine that seemed to make sense but turned out to have the opposite effect of what was hoped for. This is due to the fact that when we think mechanistically, we are not always aware of all of the mechanisms at work. Thus there is no substitute for data that provides hard clinical outcomes, such as mortality.
Other prior “I” grade recommendations have been changed when technology advanced, such as low-dose CT for lung cancer screening. But when clinical examination methods to identify early skin cancer are already pretty good, we may wonder how a new or different diagnostic modality could shift the recommendation. One possibility: artificial intelligence (AI). It may come as no surprise that there is a race to figure out how to utilize AI to identify concerning skin lesions. Neither the “ABCDE'' nor the “Ugly Duckling” rules are that hard to learn. If AI can be quick/sensitive/accurate/cheap, trained assistants could facilitate screening at shorter intervals and flag patients who might benefit from a closer look by dermatologists. AI is being developed for this right now - if this is successful and skin cancer screening becomes widely available at shorter intervals, we will need to keep an eye not just on the number of skin cancers detected, but for the hoped-for mortality reduction. For now, however, there is insufficient evidence to routinely screen for skin cancer in those at average risk.
For more information, see the topic Melanoma in DynaMed.
DynaMed EBM Focus Editorial Team
This EBM Focus was written by Dan Randall, MD, Deputy Editor at DynaMed. Edited by Alan Ehrlich, MD, Executive Editor at DynaMed and Associate Professor in Family Medicine at the University of Massachusetts Medical School; Katharine DeGeorge, MD, MS, Deputy Editor at DynaMed and Associate Professor of Family Medicine at the University of Virginia; Nicole Jensen, MD, Family Physician at WholeHealth Medical; Vincent Lemaitre, PhD, Senior Medical Writer at DynaMed; Elham Razmpoosh, PhD, Postdoctoral fellow at McMaster University; and Sarah Hill, MSc, Associate Editor at DynaMed.