A. Mutsaers1,2, E. Rival3, R. Fu4, C. Khalil5, M. Khoury5, I. Karam6, and A. Eskander4; 1Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada, 2Department of Oncology, Division of Radiation Oncology, Western University, London, ON, Canada, 3McMaster University, Hamilton, ON, Canada, 4Sunnybrook Health Sciences Centre, Toronto, ON, Canada, 5University of Toronto School of Medicine, Toronto, ON, Canada, 6Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, ON, Canada
Purpose/Objective(s): Oral Cavity Squamous cell carcinoma (OCSCC) is primarily a surgical disease, with post-operative radiation (PORT) improving locoregional control (LRC) in higher risk patients at the cost of treatment related morbidity. Opinions differ on appropriate volumes of local and regional coverage required to maximize LRC. Limited data exist on the patterns of failure in the context of PORT volumes, an important data point for clinical decision-making. Materials/
Methods: We performed a retrospective cohort study obtained from a quality-controlled database, queried for adult patients from 2000-2023 undergoing primary resection for OCSCC at a Canadian tertiary care institution. Patients receiving induction therapy, with distant metastasis, or in-situ disease were excluded. Primary outcome was LRC, defined as months from cancer diagnosis to the date of local or regional failure. Secondary outcomes included overall survival (OS) and disease-free survival (DFS). Radiation parameters including dose, fractionation, and volumes treated (primary, neck side and levels) were abstracted. Kaplan Meier method and multivariable Cox proportional hazards regressions were used to assess each of the three outcomes. Results: After exclusions, the study cohort included 1044 patients, with 38% (n=397) receiving PORT. Oral tongue was most common (55%) subsite. Patient groups were understandably imbalanced, with PORT having more advanced tumours (pT3/4 = 54% vs 8%, pN0=39% vs 40%, all standardized differences [std diff]>0.1), and patients with higher Charlson Comorbidity (CC) scores (mean 4.7 vs 2.8, std diff>0.1). Within the PORT cohort, median RT dose was 60 Gy (interquartile range 60-66) in 30 fractions. A minority (n=124/397, 31%) had concurrent chemotherapy. The total follow-up duration was similar between the two groups (mean 40 vs 44 months, std diff=0.097). At the study end, despite PORT to the primary, 21% (n=82/397) experienced local failure. In patients who had bilateral neck treatment, 18% (n=37/211) had regional failure. Local and regional failures were numerically similar (20% and 15%, respectively) in the non-PORT group. Overall, 28% developed LR failure (30% in PORT vs 27%). Distant failure rates were higher in PORT cohort (19% vs 6%). Three and 5-year LRC, DFS and OS probabilities (%) for PORT were (72, 64; 59, 52; 76, 73) respectively, compared to (75, 66; 71, 61; 88, 83) in non-PORT group. In the multivariable Cox model, any PORT was associated with improved LRC (HR 0.63, 95% CI 0.46-0.86) and DFS (HR 0.67, 95% CI 0.51-0.87), but not OS, despite the PORT group having notably worse disease and patient characteristics. Conclusion: We present a large cohort of OCSCC demonstrating that PORT is associated with improved LRC and DFS after primary surgery for OCSCC when adjusting for disease and patient factors. Future analysis will include propensity-matching and detailed predictors of failure in-and-out of radiated volumes to guide adjuvant radiation volumes.
