Tumor Upstaging With MRI for HPV-Associated Oropharynx Cancer: Implications for De-Escalation Trials.

Objectives: Human papillomavirus (HPV)-associated oropharynx cancer (OPC) requires accurate staging to guide treatment and de-escalation clinical trial enrollment. MRI provides superior soft tissue contrast and assessment of tumor depth of invasion compared with CT with contrast and FDG-PET/CT. This study aims to evaluate the prevalence of HPV-associated OPC tumor upstaging and newly identified retropharyngeal lymph node (RPLN) metastases with MRI.

Methods: Fifty consecutive patients with newly diagnosed, previously untreated HPV-associated OPC planned for treatment with primary radiotherapy at Memorial Sloan Kettering Cancer Center from March 04, 2024, to July 09, 2024, were included. All had histologic confirmation of p16-positive squamous cell carcinoma. Tumor staging and nodal assessment were independently completed by a radiation oncologist and a diagnostic neuroradiologist according to the eighth edition of the American Joint Committee on Cancer. MRI findings were compared with CT with contrast and FDG-PET/CT.

Results: The median patient age was 65, 84% were male, and 80% had <10 pack years of smoking history. Primary tumor sites included the base of tongue (50%), tonsil (48%), and glossotonsillar sulcus (2%). The rate of tumor upstaging with MRI was 12% (6/50), all 6 cases upstaged from T2 or T3 to T4. MRI identified RPLN metastases in 10% (5/50) of cases not identified on CT or PET/CT. Overall, 18% (9/50) of patients had either primary tumor upstaging or newly identified RPLN metastases based on MRI.

Conclusions: MRI leads to meaningful changes in tumor stage and RPLN detection in HPV-associated OPC. Staging MRI should be incorporated into treatment planning and de-escalation clinical trial enrollment.