Radiographic retropharyngeal lymph node involvement in HPV‐associated oropharyngeal carcinoma: Patterns of involvement and impact on patient outcomes

Abstract

Background The objective of the current study was to characterize the incidence, pattern, and impact on oncologic outcomes of retropharyngeal lymph node (RPLN) involvement in HPV‐associated oropharyngeal cancer (OPC). Methods Data regarding patients with HPV‐associated OPC who were treated at The University of Texas MD Anderson Cancer Center with intensity‐modulated radiotherapy from 2004 through 2013 were analyzed retrospectively. RPLN status was determined by reviewing pretreatment imaging and/or reports. Outcomes analysis was restricted to patients with lymph node‐positive (+) disease. Kaplan‐Meier survival estimates were generated and survival curves were compared using the log‐rank test. Bayesian information criterion assessed model performance changes with the addition of RPLN status to current American Joint Committee on Cancer staging. Competing risk analysis compared modes of disease recurrence. Results The incidence of radiographic RPLN involvement was 9% (73 of 796 patients) and was found to vary by primary tumor site. The 5‐year rates of freedom from distant metastases (FDM) and overall survival were lower in patients with RPLN(+) status compared with those with RPLN‐negative (‐) status (84% vs 93% [P = .0327] and 74% vs 87% [P = .0078], respectively). RPLN(+) status was not found to be associated with outcomes on multivariate analysis. Bayesian information criterion analysis demonstrated that current American Joint Committee on Cancer staging was not improved with the inclusion of RPLN. Locoregional and distant disease recurrence probabilities for those patients with RPLN(+) status were 8% and 13%, respectively, compared with 10% and 6%, respectively, for those with RPLN(‐) status. RPLN(+) status portended worse 5‐year FDM in the low‐risk subgroup (smoking history of <10 pack‐years) and among patients who received concurrent chemotherapy but not induction chemotherapy. Conclusions RPLN(+) status was associated with worse overall survival and FDM on univariate but not multivariate analysis. In subgroup analyses, RPLN(+) status was associated with poorer FDM in both patients with a smoking history of <10 pack‐years and those who received concurrent chemotherapy, suggesting that RPLN(+) status could be considered an exclusion criteria in treatment deintensification efforts seeking to omit chemotherapy.

Retropharyngeal Lymph Node Involvement in Oropharyngeal Carcinoma: Impact upon Risk of Distant Metastases and Survival Outcomes

“…The imaging used in prior reported series to identify RPLN (Table 4) had varied widely and would be expected to impact upon the rates of RPLN identification. In several prior series examining the incidence of RPLN in oropharyngeal carcinoma, very limited numbers of patients had PET-CT staging [12,13,20,21]. In contrast, in our series, all patients had a staging PET-CT scan in addition to MRI and/or CT.…”

“…This study analysed the impact of RPLN involvement on outcomes in a large retrospective cohort of patients with oropharyngeal carcinoma treated with chemoradiotherapy. This is the largest reported series other than the two overlapping publications from the MD Anderson Cancer Centre [13,20]. The accurate identification of RPLN involvement is critical to this analysis.…”

“…The accurate identification of RPLN involvement is critical to this analysis. Determination of abnormal RPLN was based on established radiological criteria, including size, necrosis and FDG activity [20,23,[26][27][28] by a dual-certified radiologist and nuclear medicine physician. Among patients, 84% in our series had a diagnostic MRI; MRI has been shown to be superior to contrast-enhanced CT for identification of RPLN metastases [11,29,30].…”

“…Surgical series are small and restricted to highly selected operable patients [18,19], hence limiting their applicability to the wider group of oropharyngeal carcinoma. Imaging studies have reported a very variable incidence of RPLN involvement, with larger series reporting RPLN involvement in 9-21% of oropharyngeal carcinomas [12][13][14][20][21][22][23].…”

“…Some studies have suggested that RPLN involvement in patients with oropharyngeal carcinoma is associated with inferior survival and higher risk of development of distant metastatic disease [13,15]. The prognostic implications of RPLN in patients with HPV-related oropharyngeal disease are controversial, with some, but not all, studies suggesting a negative relationship [12,15,20]. Elucidating the prognostic impact of RPLN involvement is important to accurately stratify risk in oropharyngeal carcinoma.…”