According to a new study appearing in the American Journal of Roentgenology (AJR), using a 6-mm threshold, rather than a 5-mm threshold, helps facilitate better risk stratification and treatment decisions in patients with nasopharyngeal carcinoma (NPC).
“Future American Joint Committee on Cancer (AJCC) staging updates should consider incorporation of the 6-mm threshold for N-category and tumor-stage determinations,” writes corresponding author Zhiying Liang, MD, from the radiology department at China’s Sun Yat-sen University Cancer Center.
This AJR accepted manuscript by Liang and his coauthors included 1,752 patients (median age, 46 years; 1,297 men, 455 women) with NPC treated by intensity-modulated radiotherapy from January 2010 to March 2014 from two hospitals; 438 patients underwent MRI 3-4 months after treatment. Two radiologists measured the minimal axial diameter (MAD) of the largest retropharyngeal lymph node (RLN) for each patient via consensus. Then, to assess interobserver agreement, a third radiologist measured MAD in 260 randomly selected patients. Initial ROC and restricted cubic spline analyses were used to derive an optimal MAD threshold for predicting progression-free survival (PFS).
Ultimately, in patients with NPC, overall survival was significantly different between patients with stage-I and stage-II disease defined using a 6-mm threshold (p = .04)—but not using a 5-mm threshold (p = .09). The 5-year PFS rate was associated with post-radiotherapy MAD ≥ 6 mm (HR=1.68, p=.04) but not with post-radiotherapy MAD ≥ 5 mm (HR=1.09, p=.71).
“Given the absence of a defined size threshold in the AJCC 8th Edition Staging Manual, we propose that future updates to the manual incorporate this threshold for N-category and tumor-stage determinations,” the study authors note.
Featured image: (A) Axial T2-weighted image from MRI examination performed before treatment. Largest RLN is on right side (red line) and has MAD measuring 5 mm. Patient was treated by IMRT. (B) Axial T2-weighted image obtained 3-4 months after completion of IMRT shows decrease in size of right RLN (red line), now with MAD measuring 4 mm. Patient would be considered to have RLN involvement at baseline based on ≥5-mm threshold commonly used in practice, but not by ≥6-mm threshold supported by current study. Patient would not be considered to have RLN involvement using either threshold on examination after IMRT. No disease progression, locoregional recurrence, distant metastasis, or death occurred during follow-up period of 60.7 months. NPC = nasopharyngeal carcinoma; RLN = retropharyngeal lymph node; MAD = minimal axial diameter; IMRT = intensity-modulated radiotherapy.