Clinical indicators of the development of a second oral malignancy at a previously treated cancer site : early results of a longitudinal study

Oral squamous cell carcinoma (SCC) has a poor 5-year survival rate of just over 50%, largely due to a high rate of second oral malignancies (SOM) including both recurrences and second primary tumours. Current dinicopathological indicators for oral premalignant lesions (OPLs) at high-risk of progressing into cancer are based on primary OPLs. Little is known whether these risk indicators apply to OPLs at previously treated cancer sites, which are particularly difficult to differentiate from reactive changes resulting from aggressive treatment of the tumours. Objective, to discover which clinicopathological indicators, if any, could significantly predict a SOM at the previously treated cancer site at around 1 year (8 - 16 months) after treatment of the cancer. Method. 84 patients with oral cancer (treated with intent to cure) being followed prospectively in the Oral Oncology/Oral Dysplasia Clinic were used in this thesis. Three categories of data were collected: (1) demographic and habit information (age, gender, ethnicity and tobacco habits) (2) primary tumour information (stage, site, histology and treatment of the tumour) and (3) dinicopathological features of post-treatment cancer site during follow up (the presence of an OPL, size, appearance, toluidine blue (TB) staining, histopathology and treatment of the OPLs). Results. 18 patients (21%) have developed a SOM at the treated cancer site (SOM group) within an average of 26 (± 14) months. Follow-up time for 66 patients who did not develop SOM (non-SOM group) was 28 (± 15) months. Demographics, smoking habit and features of the primary oral cancer did not predict SOM. Of the clinicopathological features of post-treatment cancer site during follow up, appearance, histopathology and treatment of OPLs did not predict SOM. There was a trend in increasing size of OPLs in the SOM group (14 ± 16 mm in diameter vs. 6 ± 5 for non-SOM group, P =0.07). However, 2 significant predictors were found. The presence of leukoplakia at the prior cancer site was significantly associated with SOM both at one-year post tumour treatment (72% vs. 15% in non-SOM group, P< 0.001) and ever during follow up (83% vs. 36%, P= 0.001). Uptake of TB stain was also significantly associated with SOM both at one-year post tumour treatment (50% vs. 11% in non-SOM group, P- 0.001) and during the entire follow-up (67% vs. 25%, P= 0.002). Conclusion: The results showed that presence of an OPL at the previous tumour site (regardless of its appearance and size) and TB positivity were significant risk predictors for SOM.Dentistry, Faculty ofGraduat