Oral cancer of the retromolar area: A study of the anatomy, pathology and natural history

This thesis centres on cancer of the retromolar triangle (RMT), an uncommon head and neck cancer. The retromolar trigone area is the region within the oral cavity defined by the American Joint Committee on Cancer (AJCC) as the attached mucosa overlying the ascending ramus of the mandible from the level of the posterior surface of the last molar tooth to the apex superiorly, adjacent to the tuberosity of the maxilla. The main points of significance about this area are that diagnosis may be delayed, the region is less accessible, and reconstruction is somewhat more difficult. Review of the literature revealed that there is a paucity of information regarding factors affecting diagnosis, treatment and prognosis of RMT cancer. The aim of this study was to assess the anatomy of the RMT and the pathology and natural history of cancer in this area to evaluate the present strategies for treatment. Gross cadaveric dissections were performed in the RMT on both sides of the oral cavity to examine the normal anatomy and to identify anatomical structures that could possibly be affected by excisional surgery. Structures liable to damage were the lingual nerve, the inferior alveolar nerve, the buccal nerve, the palatoglossus muscle, the medial pterygoid muscle, the insertion of the temporalis muscle and less frequently the submandibular duct. Damage to these structures could affect sensation, speech, swallowing and chewing. The medical records of 113 patients with histologically proven squamous cell carcinoma of the RMT, treated at Canniesburn Hospital, Glasgow, between 1985 and 1999, were reviewed retrospectively in order to study the natural history of the disease. The male: female ratio was 2.2:1 and the average age was 65 years. A total of 9.7% of patients were clinically staged as Tl, 41.6% were T2, 16% were T3 and 32.7% were T4. At presentation 71 patients (63%) had a clinically negative neck, while 85 patients (75%) had a neck dissection at the time of treatment of the primary. A comparison between the clinical and pathological T and N stages highlighted the difficulties of clinical TNM staging with upstaging of the primary T stage in 15.5% of patients and downstaging in 11% and upstaging of neck disease in 21% and downstaging in 9%. Despite advances in treatment, this series has shown no significant improvement in survival over the 15-year study period. The determinant 5-year survival rates by the Kaplan-Meier method were pTl: 75%, pT2: 40%, pT3: 47%, pT4: 32% and overall 42%. In total 34%> of patients died of disease directly related to their retromolar trigone cancer and this included 12% with systemic failure. Loco-regional failure of the retromolar trigone cancer accounted for death in 21%. The understanding of the retromolar trigone tumours as a separate entity from other intraoral squamous cell carcinomas should allow us to formulate different strategies for its treatment in the future