[Pretreatment evaluation of ¹⁸F-FDG PET-CT in extranodal NK/T-cell lymphoma]

Objective: To investigate the clinical value of pretreatment ¹⁸F-fluorodeoxy glucose positron emission tomography/computed tomography (¹⁸F-FDG PET-CT) in extranodal NK/T-cell lymphoma. Methods: Eighty-one patients with pathologically confirmed extranodal NK/T-cell lymphoma and pretreatment with PET-CT scan in Cancer Hospital, Chinese Academy of Medical Sciences from August 2006 to December 2017 were enrolled in the study. The clinical, follow-up and imaging data were analyzed retrospectively. The relationship between maximum standard uptake value (SUV_max) and prognosis were evaluated by Mann-Whitney U test and Spearman rank correlation analysis. Results: Among the 81 patients, 98.8% (80/81) were upper aerodigestive tract (UAT) involved. Lesions at extra-UAT sites were detected in 7 cases, involving parotid gland (n=1), breast (n=1), spleen (n=1), pancreas (n=1), skin and subcutaneous soft tissue (n=1), muscle (n=1), lung (n=2) and bone (n=3). Lymph node involvement were demonstrated in 33 cases. All of the lesions had increased uptake of PET, the median SUV_max was 8.6. PET-CT changed staging in 15 cases, and 12 cases were adjusted treatment methods. 21 cases were changed radiotherapy target because of PET-CT. The 1-, 2-year progression-free survival (PFS) rates were 88.7% and 80.3% while 1-, 2-year overall survival (OS) rates were 97.2% and 94.4% respectively. The median SUV_max of patients with local lymph nodes involvement was significantly higher than those without local lymph nodes involvement (P=0.007). The SUV_max was positively associated with Ann Arbor stage (r=0.366, P=0.001), lactate dehydrogenase (r=0.308, P=0.005) and Ki-67 level (r=0.270, P=0.017). The SUV_max was inversely associated with lymphocyte count (r=-0.324, P=0.003) and hemoglobin content (r=-0.225, P=0.043). Conclusions: Extranodal NK/T-cell lymphoma predominantly occurs in extra-nodal organs, mainly in the upper respiratory and gastrointestinal tracts, with marked FDG-addiction. Compared with conventional imaging, ¹⁸F-FDG PET-CT is sensitive and comprehensive in detecting extra-nodal NK/T-cell lymphoma involvement, assisting in accurate clinical staging and treatment planning. Pretreatment SUV_max is potential for prognosis evaluation since it is correlated with prognostic factors.