Pitfalls of post-treatment PET after de-intensified chemoradiotherapy for HPV-associated oropharynx cancer: Secondary analysis of a phase 2 trial

Publication date: March 2018
Source:Oral Oncology, Volume 78
Author(s): Kyle Wang, Terence Z. Wong, Robert J. Amdur, William M. Mendenhall, Nathan C. Sheets, Rebecca Green, Brian D. Thorp, Samip N. Patel, Trevor G. Hackman, Adam M. Zanation, Mark C. Weissler, Bhishamjit S. Chera
ObjectivesWe evaluated patterns of nodal response and positive predictive value (PPV) of 3 month post-treatment PET in patients with HPV-associated oropharyngeal cancer treated on a multi-institutional de-intensification trial.Materials and methodsEligibility criteria included: (1) T0-3, N0-2c, M0, (2) HPV+/p16+ oropharyngeal squamous cell carcinoma, and (3) ≤10 pack-years smoking or ≤30 pack-years and abstinent ≥5 years. Patients received 60 Gy radiation alone (T0-2, N0-1) or with concurrent weekly cisplatin 30 mg/m² and surveillance PET three months post-radiation. Nodal responses were categorized as complete (CR), equivocal (ER), or incomplete (IR) using both local and central radiographic review. A "true positive" was ER/IR with clinical/radiographic progression or positive pathology.Results79 node-positive pts (84% N2) were analyzed. Distribution of nodal CR, ER, and IR was 44 (56%), 27 (34%), and 8 (10%), respectively. 29 (37%) had ER/IR in pre-treatment node-positive neck levels, whereas 14 (18%) had ER/IR in pre-treatment node-negative levels. Of patients with ER/IR, 5 were observed clinically, 19 received repeat imaging, and 11 received either biopsy (1) or neck dissection (10). The PPV was 9% for ER/IR and 13% for IR, with 3 patients found to have persistent disease on neck dissection. There was no difference in nodal relapse rate in patients with nodal CR vs. nodal ER/IR.ConclusionPost-treatment PET may not accurately predict the presence of persistent disease in patients with favorable-risk oropharynx cancer. These results support close surveillance rather than surgical evaluation in most favorable-risk patients.



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