Association Between Health Maintenance Practices and Skin Cancer Risk as a Possible Source of Detection Bias.

Importance: Detection bias may influence the results of epidemiologic studies of skin cancer risk. An individual's degree of contact with the health care system, and, specifically, undergoing routine screening practices, may be a source of such bias. More intensive screening practices may be associated with increased diagnoses of basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and melanoma. Objective: To assess a possible association between health care screening practices and skin cancer risk. Design, Setting, and Participants: The cohort of participants for this study was drawn from the Nurses' Health Study (121 700 women) and Health Professionals Follow-up Study (51 529 men). Participants in the Nurses' Health Study were followed up from June 1, 1990, to June 1, 2012, and participants in the Health Professionals Follow-up Study were followed up from January 1, 1990, to January 1, 2012. Statistical analysis was performed from April 4, 2017, to May 16, 2018. Exposures: During cohort follow-up, Nurses' Health Study and Health Professionals Follow-up Study participants were asked whether they had undergone various health care screening practices including physical examination by a physician, sigmoidoscopy or colonoscopy, eye examination, serum cholesterol test, mammography, breast examination and pelvic examination, and prostate-specific antigen test and rectal examination. Main Outcomes and Measures: Incident BCC, SCC, and invasive melanoma. Cases of SCC and melanoma were confirmed with histopathologic findings. Hazard ratios (HRs) with 95% CIs were calculated for the association between screening practices and the various types of skin cancer. Results: This study included 77 736 women from the Nurses' Health Study (mean [SD] age at baseline, 56 [7] years) who were followed up for 1 388 523 person-years and 39 756 men from the Health Professionals Follow-up Study (mean [SD] age at baseline, 58 [10] years) who were followed up for 635 319 person-years. A total of 14 319 incident BCCs, 1517 SCCs, and 506 melanomas were identified in the Nurses' Health Study cohort and 8741 incident BCCs, 1191 SCCs, and 469 melanomas were identified in the Health Professionals Follow-up Study cohort. Positive associations were seen between various screening practices and diagnoses of BCC and SCC, with similar directions of associations seen with melanoma for some screening practices. In the Nurses' Health Study, the multivariable HR associated with undergoing a physical examination was 1.46 (95% CI, 1.30-1.64) for BCC, 2.32 (95% CI, 1.41-3.80) for SCC, and 1.66 (95% CI, 0.85-3.22) for melanoma. Similar results were seen in the Health Professionals Follow-up Study, with a multivariable HR associated with undergoing a physical examination of 1.43 (95% CI, 1.26-1.63) for BCC and 1.85 (95% CI, 1.17-2.92) for SCC, with an attenuated HR for melanoma of 1.04 (95% CI, 0.64-1.69). Conclusions and Relevance: Undergoing health care screening practices increases the likelihood of being diagnosed with skin cancer. Researchers should be aware of this association and, where appropriate and possible, condition analyses of skin cancer risk on measures of health care use, including screening, to address confounding associated with detection bias.