Impact of a second FDG PET scan before adjuvant therapy for the early detection of residual/relapsing tumours in high-risk patients with oral cavity cancer and pathological extracapsular spread

PURPOSE: Extracapsular spread (ECS) to the cervical lymph nodes is a major adverse prognostic factor in oral cavity squamous cell carcinoma (OSCC). We prospectively examined the value of FDG PET immediately before postoperative radiotherapy/concurrent chemoradiotherapy (pre-RT/CCRT PET) to detect residual/relapsing disease in the early postsurgical follow-up period in high-risk OSCC patients with ECS.

METHODS: We examined 183 high-risk OSCC patients with ECS who underwent preoperative FDG PET/CT for staging purposes. Of these patients, 29 underwent a second pre-RT/CCRT FDG PET/CT scan. The clinical utility of the second FDG PET/CT was examined using Kaplan-Meier curve analysis.

RESULTS: Patients who underwent the second FDG PET/CT scan had baseline clinicopathological characteristics similar to those who did not undergo a second scan. Of the patients who underwent the second scan, seven (24 %) had unexpected, newly discovered lesions. Five eventually died of the disease, and two had no evidence of recurrence after a change in RT field and dose. In an event-based analysis at 2 months, rates of neck control (6/29 vs. 6/154, p = 0.001), distant metastases (3/29 vs. 4/154, p = 0.046), and disease-free survival (7/29 vs. 10/154, p = 0.003) were significantly higher in patients who received a second PET scan than in those who did not. The second pre-RT/CCRT PET scan was of particular benefit for detecting new lesions in OSCC patients with both ECS and lymph node standardized uptake value (SUV) of ≥ 5.2 in the first PET scan.

CONCLUSION: The present findings support the clinical value of pre-RT/CCRT FDG PET for defining treatment strategy in OSCC patients with both ECS and high nodal SUV, even when FDG PET had already been performed during the initial staging work-up.