Nasopharyngeal carcinoma: relationship between 18F-FDG PET/CT maximum standardized uptake value and lesion size with TNM classification

Abstract

Objectives: To evaluate the relationship between tumour SUVmax and size and TNM staging in patients with nasopharyngeal carcinoma (NPC).

Methods: We retrospectively analyzed the PET/CT findings of 25 consecutive patients (age range 15-80 yrs, mean 51.1 ± 14.3) with histologically proven NPC at initial diagnosis (n=11) or recurrence (n=14) over a 8-month period. Histological type was undifferentiated carcinoma in all except one of squamous cell carcinoma. All pts were scanned prior to commencement of treatment or had completed treatment at least 1-year ago. SUVmax of the 18F-FDG-avid lesion in the nasopharynx and maximum diameters were measured on axial PET reconstruction and the co-registered contrast-enhanced CT scan respectively by two radiologists in consensus blinded to the clinical details. All patients were staged using the AJC/UICC TNM staging system. Multiple linear regression analysis was performed to study the simultaneous influence of tumour SUVmax and size on T-, N-, and M staging.

Results: Mean SUVmax and tumour size was 5.6 ± 3.91 (range: 1.80 – 16.00) and 4.58 ± 5.92 cm2 (range: 0.18 – 27.5), respectively. Using univariate analysis, there were significant correlations between T-stage and tumour size (r=0.671, p<0.001), T-stage and SUVmax (r=0.436, p=0.030) and tumour size and SUVmax (r=0.758, p<0.001). Multiple linear regression analysis revealed tumour size to be the only independent variable that significantly affected T-stage (adjusted R2=0.351, p=0.003). Similar results were found when new and recurrent cases were separately analyzed.

Conclusions: No significant correlation was found between SUVmax of the primary tumour and the TNM stages. Tumour size was the only independent predictor of T-stage.