18F-FDG PET/CT in primary systemic anaplastic large cell lymphoma (ALCL): Differential FDG uptakes according to anaplastic lymphoma kinase (ALK) expression

561 Objectives Primary systemic ALCL is a kind of non-Hodgkin’s T-cell lymphoma and accounts for 2~8% of lymphoma. We evaluated the role of FDG PET/CT in primary systemic ALCL and assessed whether there are any differential PET/CT findings according to ALK expression. Methods Thirty-four patients (15 ALK+, 19 ALK-) with primary systemic ALCL who had baseline PET/CT before chemotherapy, from 2004 to 2011, were retrospectively reviewed. ALK expression was proven by immunohistochemistry staining. PET/CT images were analyzed visually and semi-quantitatively using peakSUV. In 24 patients (10 ALK+, 14 ALK-) who underwent interim PET/CT after at least 3 cycles of CHOP-based chemotherapy, PET/CT images were also evaluated for assessing the treatment response and progression-free survival. Results The baseline PET/CT of all 34 patients showed moderate-to-high FDG-avidity (peakSUV 15.0±8.6, range 5.5~38.6) with involvement of nodal and/or extra-nodal sites. The peakSUV of ALK+ ALCL was significantly higher than that of ALK- ALCL (20.5±9.7 vs. 10.7±4.2, p=0.006). In the receiver operating characteristics curve analysis, the sensitivity and specificity for differentiating ALK expression were 84.6% and 86.7% with a cut-off value of peakSUV 12.4(AUC=0.85). On visual analysis of interim PET/CT of 24 patients, 13 patients had no FDG-avid lesion with complete response (negative interim PET/CT). The 3-year progression-free survival was 77% for patients with a negative interim PET/CT, whereas 45.5% for patients with a positive interim PET/CT (p=0.14). Conclusions In baseline PET/CT, all patients with primary systemic ALCL showed moderate-to-high FDG-avidity, and ALCL with ALK expression showed higher FDG uptake than ALCL without ALK expression. Patients with negative interim PET/CT after chemotherapy tended to have better progression-free survival in primary systemic ALCL