Incidence of Radiographically Occult Nodal Metastases in HPV+ Oropharyngeal Carcinoma: Implications for Reducing Elective Nodal Coverage

Publication date: Available online 27 March 2018
Source:Practical Radiation Oncology
Author(s): Gokoulakrichenane Loganadane, Jacqueline R. Kelly, Nicholas C. Lee, Benjamin Kann, Amit Mahajan, James E. Hansen, Yazid Belkacémi, Wendell Yarbrough, Zain Husain
PurposeInitial de-escalation studies for HPV-driven oropharyngeal squamous cell carcinomas (HPV+ OPSCC) altered radiotherapy dose or the systemic agent used. Newer trials examine the disease control achieved with a reduced elective nodal field. We examined patterns of nodal involvement in patients with HPV+ OPSCC with a focus on implications for radiation field design for treatment de-escalation.Methods and materialsRecords of patients with HPV+ OPSCC with preoperative imaging (CT or FDG-PET/CT) who underwent neck dissection without neoadjuvant therapy from 2010 to 2017 were retrospectively reviewed. The number and location of clinically positive lymph nodes on preoperative imaging were compared with those documented on pathology. These data were then used to establish the probability of missing nodal disease in three modified radiation field designs.ResultsOne hundred patients were included. The median time between imaging and surgery was 22 days. The most common clinical N stage was cN2a (35%), while the most common pathologic N stage was pN2b (45%). The median number of radiographically and pathologically involved nodes was 1 (range 0-6) and 2 (range 0-11), respectively. 43% of patients had more pathologically involved nodes than predicted on imaging, while 21% had pathologic involvement at an additional nodal level not predicted on imaging. Of the 21 patients with additional pathologically involved nodal levels, 14 had involvement of a directly adjacent station, four were patients with a cN0 hemineck with pathologically positive level II disease, and three had pathologic involvement of a level two echelons removed from that predicted on imaging.ConclusionOur study suggests that radiation fields encompassing only clinically involved nodes or levels has an unacceptably high likelihood of missing subclinical disease. Alternatively, treating the first uninvolved echelon nodes in addition would cover pathologic sites of disease in 97% of patients. This approach merits further study in prospective trials.



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