Rapid In-Field Failures Following Adjuvant Radiation for Buccal Squamous Cell Carcinoma

Abstract

Squamous cell carcinoma originating in the buccal mucosa and retromolar trigone (RMT) have historically poor outcomes. Difficulties in discriminating tumor origin often result in these subsites being combined in surgical and pathological reports. We aimed to determine if making this anatomical distinction has implications for treatment design and clinical outcomes. Following institutional review board approval, we reviewed all of our oral cavity cases from the last 10 years and identified 27 tumors from either the buccal mucosa or RMT which underwent surgery with reconstruction followed by radiation therapy. We reviewed all pre-operative imaging and examination reports to accurately determine the site of origin. For patients who developed a local failure, we fused the pre-treatment imaging, simulation CT, and follow up imaging to determine the location of failures relative to the radiation field. All recurrences were biopsy proven. We used the Kaplan-meier method to calculate 2-year locoregional control and 2-year disease free survival. Patient characteristics can be found in table 1. The median prescribed radiation dose was 60 Gy and the median time from surgery to radiation was 50 (32-133) days. The 2-year locoregional control rates for buccal mucosa versus RMT respectively were 32.7% versus 68.4%. The 2-year disease free survival rates were 35.9% versus 68.4%. The median times to failure were 12.00 (4.9-115.0) months versus 18.5 (4.5-61.0) months. All buccal mucosa failures occurred within the high dose PTV with a median dose of 60 Gy within the failure region. Following locoregional failure 10 of the 12 patients have died, with a median time from local failure to death of 109 (4-529) days. Squamous cell carcinomas of the buccal mucosa have a dismal prognosis characterized by rapid in field failure. By contrast, RMT cancers may have more favorable outcomes. Therefore, differentiating tumor origin is important for prognostication and treatment. For buccal cancers, interval diagnostic imaging before radiation and treatment intensification should be explored.Abstract MO_6_2507; Table 1Patient CharacteristicsCharacteristicBuccal n=13 (%)RMT n=14 (%)Median Age (y)5857Male10 (77)12 (86)Female3 (23)2 (14)T stageT13 (23)2 (14)T24 (31)2 (14)T301 (7)T4a6 (46)8 (57)T4b01 (7)N stageN09 (69)5 (36)N12 (15)2 (14)N2a00N2b2 (15)7 (50)Overall StageI2 (15)0II4 (31)1 (7)III02 (14)IVA7 (54)10 (71)IVB01 (7)Positive Margin4 (31)8 (57)PNI4 (31)6 (43)LVSI1 (8)6 (43)ECE1 (8)5 (36)Chemo6 (46)7 (50)RT Dose (Median)6066 Open table in a new tab