Incidence of small lymph node metastases in patients with nasopharyngeal carcinoma: Clinical implications for prognosis and treatment

Background: Patients with nasopharyngeal carcinoma (NPC) often present small lymph nodes. The purpose of this study was to determine the prognostic impact on local recurrence of small lymph nodes, defined as smaller than 10 mm in greatest diameter. Methods: Consecutive patients treated by intensity-modulated radiotherapy (IMRT) for pathologically confirmed NPC were analyzed retrospectively. Those without small lymph nodes were excluded from the study. From January 2005 to January 2011, 275 patients with NPC represented with 2722 small lymph nodes, which were analyzed. Small lymph node axial diameter was measured using CT/MRI before radiotherapy (RT), at 50 Gy, and 6 months after the end of RT. The dose received by the small lymph nodes and the changes in lymph node diameter were recorded. Clinical endpoints were overall survival (OS), locoregional control, disease-specific survival (DSS), and distant metastasis-free survival. Median follow-up time was 55 months (range, 5–96 months). Results: Patients were grouped according to the dose received by the small lymph nodes and the number of small lymph nodes. Only 27 patients (9.8%) had a decrease ≥50% in the small lymph node diameter at 50 Gy and 53 patients (19.3%) had a decrease ≥50% at 6 months after RT. The 5-year locoregional control, distant metastasis-free survival, DSS, and OS were 93.5%, 85.2%, 88.8%, and 87.0%, respectively. Multivariate analyses showed that T classification and N classification are independent prognostic factors for OS. However, the dose received and the numbers of small lymph nodes were not statistically associated with any of the survival endpoints. Conclusion: In the IMRT era, N classification remains an independent prognostic factor in NPC. However, the incidence of small lymph nodes is not a significant prognostic factor in patients with NPC. The presence of small lymph nodes should not influence the nodal contouring or the dose delivered to nodal areas.