High-risk factors of parotid lymph node metastasis in nasopharyngeal carcinoma: a case-control study

BACKGROUND Although parotid-sparing IMRT decreased the dose distribution of parotid, parotid region recurrence has been reported. Prophylactic irradiation in parotid area would be necessary in patients with high risk of parotid lymph node metastasis (PLNM). This study was to detect the high-risk factors of PLNM in nasopharyngeal carcinoma. METHODS This was a 1:2 case-control study. All patients in this study were newly diagnosed NPC with N2-3 classification from January 2005 to December 2012. Cases were 22 sides with ipsilateral PLNM. Controls were 44 patients who were randomly selected from N2-3 disease in database. RESULTS 20/1096 (1.82 %) NPC patients were found PLNM. Sum of the longest diameter for multiple lymph nodes (SLD) in level II was larger in case group than that in control group (6.0 cm vs. 3.6 cm, p = 0.003). Level II lymph node necrosis, level Va/b involvement, and rare neck areas involvement were more common in case group (p = 0.016, p = 0.034, and p < 0.001, respectively). RPN, level III, and level IV metastases showed no significant difference between the two groups. Multivariate analysis in logistic regression showed that only SLD ≥5 cm in II area (OR = 4.11, p = 0.030) and rare neck areas involvement (OR = 3.95, p = 0.045) were associated with PLNM in NPC patients. CONCLUSIONS PLNM was an uncommon event in NPC patients. SLD ≥5 cm in level II and involvement in rare-neck areas may be potentially high-risk factors for PLNM. Sparing parotid in IMRT was not recommended for NPC patients with high risks of PLNM.