Oral Squamous Cell Carcinoma Found Inline with the Fields of Repeat Stereotactic Radiosurgery for Recurrent Trigeminal Neuralgia

A case of an extremely healthy, active, 96-year-old patient, nonsmoker, is reviewed. He was initially treated for left V1, V2, and V3 trigeminal neuralgia in 2001, at age 80, with stereotactic radiosurgery (SRS) with a dose of 80 Gy to the left retrogasserian trigeminal nerve. He remained asymptomatic for nine years until his trigeminal pain recurred in 2010. He was first treated medically but was intolerant to increasing doses of carbamazepine and gabapentin. He underwent a second SRS in 2012 with a dose of 65.5 Gy to the same retrogasserian area of the trigeminal nerve, making the total cumulative dose 125.5 Gy. In late 2016, four years after the 2(nd) SRS, he was found to have invasive keratinizing squamous cell carcinoma in the left posterior mandibular oral mucosa. Keratinizing squamous cell carcinoma is seen primarily in smokers or associated with the human papillomavirus, neither of which was found in this patient. A review of his two SRS plans shows that the left lower posterior mandibular area was clearly within the radiation fields for both SRS treatments. It is postulated that his cancer developed secondary to the long-term radiation effect with a very localized area being exposed twice to a focused, cumulative, high-dose radiation. There are individual reports in the literature of oral mucositis immediately after radiation for trigeminal neuralgia and the delayed development of malignant tumors, including glioblastoma found after SRS for acoustic neuromas, but there are no reports of delayed malignant tumors developing within the general radiation field. Using repeat SRS is an accepted treatment for recurrent trigeminal neuralgia, but physicians and patients should be aware of the potential effects of higher cumulative radiation effects within the treatment field when patients undergo repeat procedures.