Cancer risk of Lichen planus: A cohort study of 13,100 women in Finland

The association between Lichen planus (LP) and cancer has been under debate for decades. We studied the connection via population‐based Finnish register data. All women with the diagnosis of LP (n = 13,100) were identified from the Finnish Hospital Discharge Registry from 1969–2012. These patients were linked with subsequent cancer diagnoses from the Finnish Cancer Registry until 2014. Standardized incidence ratios (SIRs) were counted for different cancers by dividing the observed numbers of cancers by expected numbers, which were based on national cancer incidence rates. In total, 1,520 women with LP were diagnosed with cancer (SIR 1.15, 95% confidence interval [CI] 1.09–1.20). LP was associated with an increased risk of cancer of lip (SIR 5.17, 95% CI 3.06–8.16), cancer of tongue (SIR 12.4, 95% CI 9.45–16.0), cancer of oral cavity (SIR 7.97, 95% CI 6.79–9.24), cancer of esophagus (SIR 1.95, 95% CI 1.17–3.04), cancer of larynx (SIR of 3.47, 95% CI 1.13–8.10) and cancer of vulva (SIR 1.99, 95% CI 1.18–3.13). The risk of cancer was not increased in other locations where LP manifests (pharynx and skin). Patients with diagnosed LP have an increased risk of developing cancer of lip, tongue, oral cavity, esophagus, larynx and vulva. These data are important when considering treatment and follow‐up of patients with LP diagnosis.