Incidence and location of metastatic disease in 369 patients with HNSCC imaged using PET/CT: impact on PET/MRI protocol design.

1578 Objectives Post-treatment surveillance in HNSCC relies on cross sectional imaging, including CT, MRI, and/or PET/CT in addition to clinical examination[1, 2]. PET/CT has the benefit of high sensitivity and specificity for early disease detection[3]. Determining optimal surveillance strategy relies also in determining the best timing and the ideal extent (full body vs. limited) of imaging in the post-treatment setting[4, 5]. This retrospective study aims to determine the timing, location, and extent of disease recurrence in patients treated for HNSCC. We hope these data can inform the need for whole-body versus bed-specific imaging using PET/MRI at different stages of patients with HNSCC. Methods A retrospective, HIPAA approved, study searched a pathology database for patients with pathology proven HNSCC. Patients with nasopharyngeal carcinoma were excluded from the dataset. The number and location of disease recurrence was obtained in all patients who underwent imaging with PET/CT. Locations of disease recurrence were identified as either local or distant, and specific locations of recurrence were tabulated for each study. Results A total of 141 underwent initial pre-treatment baseline PET/CT, and subsequent surveillance PET/CT between the years of 2011-2014. There were a total of 369 patients (80% male, 20% female) with a mean age of 60 (SD 12, min 22 max 95, range 73). Of these, 24 patients had a synchronous second primary malignancy at presentation. A total of 140 cases out of 141 had some degree of local activity at baseline evaluation, 186 (53%) at first follow up, 51 cases (37%) at second follow up, 19 cases (34%) at third follow up, and 9 cases (45%) at fourth follow up. There were a total of 2 (1%) patients who presented with distant disease at the time of baseline PET/CT. At first follow up, there were 30 instances (8.1%) of distant disease, 26 instances (19%) at second follow up, 14 instances (25%) at third follow up, and 8 instances (40%) at fourth follow up. A total of 701 PET/CT scans performed, which identified 80 foci (11.4%) of hypermetabolic activity in 50 patients (13.6%) beyond the neck. Of the 80 instances of disease identified beyond the neck, most common locations of disease were lung (41 cases, 82%), bone (10 cases, 20%), liver (4 cases, 8%), mediastinum (2 cases, 4%), paraesophageal (1 case, 2%), and diaphragm (1 case, 2%). Conclusions: There were 30 cases of distal disease at first follow up (29, 97% of which was to the lungs), compared to 2 cases at baseline PET/CT. The percentage of cases of distal disease decreased to 19% at second follow up, but the disease was only limited to the lung in 77% of cases (6 cases, 23% of osseous metastases) suggesting that full body imaging is important at this time point. Additionally, there was a high percentage of patients with local hypermetabolic activity at initial presentation (99%), and first follow up (53%), reiterating that local disease surveillance is necessary in the immediate post-treatment setting. The majority of cases of distant metastases were limited to the lungs at first follow up (97%) and baseline (100%). These data suggest that PET/MRI performed as the baseline scan after the completion of chemoradiation, may not require whole body PET/MRI, but rather can focus on evaluating local response to treatment[6]. Additionally, given the high incidence of pulmonary metastases, PET/MRI of the neck paired with a chest CT may be the most appropriate staging test immediately after initial treatment.