Clinicopathological risk factors of oral second primary tumours.

Background: Oral second primary tumours (SPTs) have a poor prognosis due to late-stage diagnosis. This study evaluates the demographic and clinicopathological risk predictors of SPTs. Methods: Patients with oral squamous cell carcinoma, carcinoma in situ, or severe dysplasia were accrued into the Oral Cancer Prediction Longitudinal study within one year post-curative treatment. Data on demographics, risk habits, and primary tumour characteristics were collected. Clinical follow-up included assessing the presence of second oral premalignant lesions (SOPLs), clinicopathological features, and the results from toluidine blue staining and fluorescence visualization. Results: Among 296 patients, 23 (8 %) developed SPTs. Older age at primary cancer diagnosis (P = 0.008) and a history of chewing tobacco or betel nut (P = 0.043) increased the risk of SPTs. Patients with primary tumours located at low-risk sites had an increased risk of SPTs (P = 0.004), which often presented at high-risk sites. The presence of SOPLs (P < 0.001), and multiple lesions (P = 0.017) significantly increased the risk of SPTs. Positive toluidine blue staining indicated a trend toward higher risk of SPTs, whereas fluorescence visualization did not. The median time to SPT diagnosis was 3.25 years post-treatment. Conclusions: Identifying second or multiple oral premalignant lesions is critical for predicting the risk of SPTs regardless of their clinical or histological characteristics. Routine biopsy of these lesions should be prioritized to ensure timely diagnosis. Incorporating these risk predictors into clinical follow-up can enhance early cancer detection and improve patient outcomes.