Interesting ImagesDetection of Residual Tumor With 68Ga-Pentixafor PET/CT in a Patient With Waldenström Macroglobulinemia and Concurrent John Cunningham Virus–Related Progressive Multifocal LeukoencephalopathyPan, Qingqing MD∗,‡; Luo, Yaping MD∗,‡; Qian, Min MD†Author Information From the Departments of ∗Nuclear Medicine †Neurology, Chinese Academy of Medical Sciences and Peking Union Medical College Hospital ‡Beijing Key Laboratory of Molecular Targeted Diagnosis and Therapy in Nuclear Medicine, Beijing, China. Received for publication May 10, 2020; revision accepted July 6, 2020. Conflicts of interest and sources of funding: The authors declared no conflicts of interest. This work is supported by the National Natural Science Foundation of China (81701741) and the CAMS Innovation Fund for Medical Sciences (2017-I2M-3-001). Correspondence to: Yaping Luo, MD, Department of Nuclear Medicine, Chinese Academy of Medical Sciences and Peking Union Medical College Hospital, Dongcheng District, Beijing 100730, China. E-mail: email@example.com. Clinical Nuclear Medicine: October 2020 - Volume 45 - Issue 10 - p 792-794 doi: 10.1097/RLU.0000000000003250 Buy Metrics Abstract A 75-year-old man diagnosed with Waldenström macroglobulinemia (WM) complained of neurological symptoms. Baseline 18F-FDG PET/CT showed diffusely increased radioactivity in the bone marrow and decreased FDG uptake in the right cerebellum. After rituximab-containing immunochemotherapy, the patient had clinically partial response of WM, but the cerebellar lesion was enlarged. Repeated 18F-FDG PET/CT was similar to the baseline. 68Ga-pentixafor PET/CT detected residual tumor of WM in occipital bone and cervical lymph nodes, but there was no uptake in the cerebellar lesion. Finally, John Cunningham virus–related progressive multifocal leukoencephalopathy was confirmed. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.