The Malignant Transformation Rate of Oral Carcinoma In Situ

Objectives: Oral carcinoma in situ (OCIS) is a Stage 0 malignant condition known to progress to invasive oral squamous cell carcinoma (OSCC). The rate and timeframe of this transformation are not well delineated. We present the largest study to date investigating the malignant transformation rate of OCIS to invasive OSCC. Methods: We performed a retrospective cohort analysis using the TriNetX Research database. Patients ≥ 18 years of age with a diagnosis of OCIS from 2008 to 2018 were included, allowing for up to 5 years of follow-up. The primary outcome was the 5-year rate of OSCC transformation compared to an age-matched control cohort. Secondary objectives included a description of treatment pathways and 5-year survival. Descriptive and comparative statistics were conducted using TriNetX software. Results: About 4130 patients diagnosed with OCIS were included. Mean age at diagnosis was 62.5 ± 13.1 with patients being 61.0% male (n = 2521), 74.0% white (n = 3058), and 73.3% not Hispanic/Latino (n = 175). Patients with OCIS had 15.3% nicotine dependence (n = 15.3) and 7.5% alcohol dependence (n = 308). The 5-year malignant transformation rate for OCIS to OSCC was 56.8% (n = 2349), with the mean time to transformation being 15.0 months. Patients had a 234.9 times greater risk of developing OSCC compared to the control (95% CI 126.4–436.5, p < 0.01). Five-year Kaplan–Meier survival probability for OCIS was 74.7%. Conclusions: Our results indicate a high rate of malignant transformation from OCIS to OSCC. A mean transformation time of 15 months underscores the need for prompt work-up and treatment. Level of Evidence: Retrospective cohort study—Level 3.