Determining the potential for malignant transformation of oral lichen planus (OLP) is complicated by difficulties in diagnosis, differentiation from oral lichenoid lesions (OLLs) and the phenomenon of premalignant lesions' exhibiting lichenoid characteristics. The authors of this systematic review evaluated evidence regarding malignant transformation of OLP and characterized transformation prevalence, clinical characteristics of OLP lesions developing into squamous cell carcinoma (SCC) and time to transformation.

The authors searched PubMed, Embase and Thomson Reuters Web of Science in a systematic approach. They evaluated observational English-language studies involving human participants published in peer-reviewed journals. Inclusion required patients to have the diagnosis of OLP or OLL as confirmed with biopsy results on initial enrollment. They excluded all patients who had dysplasia on initial biopsy of OLP or OLL lesions.

Sixteen studies were eligible. Among 7,806 patients with OLP, 85 developed SCC. Among 125 patients with OLL, four developed SCC. The rate of transformation in individual studies ranged from 0 to 3.5 percent. The overall rate of transformation was 1.09 percent for OLP; in the solitary study in which investigators evaluated OLL, the rate of transformation was 3.2 percent. Patients' average age at onset of SCC was 60.8 years. The authors noted a slight predominance of female patients among those who experienced malignant transformation. The most common subsite of malignant transformation was the tongue. The average time from diagnosis of OLP or OLL to transformation was 51.4 months.

A small subset of patients with a diagnosis of OLP eventually developed SCC. The most common demographic characteristics of patients in this subset were similar to the most common demographic characteristics associated with OLP in general (that is, being female, being older and being affected in areas common to this condition). It is prudent for clinicians to pursue continued regular observation and follow-up in patients with these conditions, even in patients who do not fit a traditional high-risk category for oral SCC.