Recent research studies have linked rosacea to an increased risk of a variety of malignancies including thyroid cancer, basal cell carcinoma, glioma, hepatic cancer, breast cancer, and nonmelanoma skin cancers.1 Though the pathogenesis of rosacea is poorly understood, rosacea and cancer are thought to be linked by the commonality of inflammatory and immune response dysfunction.2 In examining the relationship between rosacea and cancer, it is important to understand the difference between relative and absolute risk.
Absolute risk is the probability of an event occurring, while the relative risk is a comparison ratio of the probability of an event occurring in the exposed group against the probability of an event occurring in the non-exposed group. The difference between the absolute risk in the exposed group and the non-exposed group is the attributable risk, a clinically useful value used to determine the amount of risk a patient faces (Figure). This is often expressed as numbers needed to treat; for example, the number of patients with rosacea who would need to be seen before there is a single additional case of cancer due to rosacea. Unfortunately, clinicians are often provided only relative risk estimates instead of absolute estimates of adverse outcomes, which, in this analysis, is the risk of developing cancer in a patient with a history of rosacea.
A recent analysis of a PubMed search of cohort studies in which rosacea was associated with malignancy calculated the attributable risks of thyroid cancer, glioma, and hepatic cancer to be 1.41, 1.44, and 0.46 per 10,000 patient-years, respectively.1 Hence, the numbers of rosacea patients needed to be treated in 1 year to attribute one additional case of these cancers to rosacea were 7080, 6963, and 21645, respectively.1 While these cancers may be more common in patients with rosacea than in the general population, they are still rare events; the increased risk is of questionable significance; and the minute increase in risk alone does not imply that patients with rosacea need to be screened for these cancers.
A survey distributed to 139 practicing internists and residents at the Colorado Chapter of the American College of Physicians found that physicians demonstrated an inclination to obscure the difference between relative risk and absolute risk in affiliation with cancer screens.3 Furthermore, a similar pattern was shown by a questionnaire study, in which approximately 32% of physicians agreed with the following inaccurate statement: “Being diagnosed with rosacea increases the chance of developing hepatocellular carcinoma by 42%. This means that for every 10 people who developed rosacea, about 4 people will get hepatocellular carcinoma.”1,3 On the contrary, over 20,000 patients would have to be seen in 1 year to attribute a case of hepatocellular carcinoma to rosacea.1
Although studies associate rosacea with an increased risk of malignancy, the risk represents a relative risk and must be appropriately evaluated, not exaggerated. While cancer screenings may provide benefit, they can lead to unnecessary costs, complications, and anxiety in patients. Physicians should gain a better understanding of relative and absolute risk to accurately assess and educate patients. Furthermore, additional studies using absolute indicators are needed to gain further insight into the relationship between rosacea and malignant comorbidities.
Maureen Ezekor, BBA, is a MD candidate at The University of Texas Medical Branch, School of Medicine.
Steven Feldman, MD, PhD, is a professor of dermatology at Wake Forest School of Medicine, Department of Dermatology.
1. Tjahjono LA, Cline A, Huang WW, Fleischer AB Jr, Feldman SR. Rosacea: relative risk vs absolute risk of malignant comorbidities [published ahead of print January 14, 2019]. J Am Acad Dermatol. doi:10.1016/j.jaad.2019.01.013.
2. Li WQ, Zhang M, Danby FW, Han J, Qureshi AA. Personal history of rosacea and risk of incident cancer among women in the US. British J Cancer. 2015;113(3):520.
3. Caverly TJ, Prochazka AV, Binswanger IA, Kutner JS, Matlock DD. Confusing relative risk with absolute risk is associated with more enthusiastic beliefs about the value of cancer screening. Medical Decision Making. 2014;34(5):686-692.