Risk stratification and corresponding postoperative treatment strategies for occult contralateral lymph node metastasis in pyriform sinus squamous cell carcinoma patients with ipsilateral node-positive necks

BACKGROUND: To quantitatively predict the probability of occult contralateral lymph node metastasis (cLNM) for pyriform sinus squamous cell carcinoma (PSSC) patients with ipsilateral node-positive necks to guide postoperative adjuvant treatment. METHODS: Two hundred and twenty-seven PSSC patients with ipsilateral lymph node metastasis (iLNM) were retrospectively analyzed. RESULTS: Multivariate logistic analyses showed that five factors including maximum tumor diameter (MTD) of more than 4.0 cm, existence of tumor extension across the midline (EAM), internal jugular vein adhesion (IJVA), lymphovascular invasion (LVI), and lymph nodal fusion (LNF) were independent risk factors for cLNM. A predictive nomogram was created based on these factors. The accuracy and validity of our model were verified by concordance index (C-index) 0.862 [95% confidence interval (CI): 0.810–0.914] in development cohort and 0.860 (95% CI: 0.820–0.900) after 1,000 bootstrapping. The calibration curve also showed a relatively favorable agreement. We then stratified patients into three groups based on their cLNM risk scores. Possible cLNM rates for low-risk, moderate-risk, and relatively high-risk subgroups were 3.6%, 21.8%, and 60.7%, respectively. CONCLUSIONS: A new postoperative adjuvant radiotherapy (PART) strategy selection flow chart was created for PSSC patients based on our newly built nomogram which can effectively predict the individualized possibility of cLNM. For patients in high-risk subgroup, therapeutic-dose PART is highly recommended even for those with contralateral clinical N0 neck disease. For those in moderate-risk subgroup, prophylactic-dose PART is recommended. However, for patients in low-risk subgroup, regular follow-up is sufficient given the extremely low occult cLNM rate.