Evolution of 18F-FDG Uptake as a Pitfall of Image Diagnosis for Systemic Anaplastic Large Cell Lymphoma.

In most patients, systemic anaplastic large cell lymphoma (sALCL) is an 18F-FDG-avid tumor. Both ALK-positive and ALK-negative tumors can be evaluated by PET scans as both tumor types uptake 18F-FDG in PET. The PET scan is also valuable in predicting prognosis during and after the treatment course. The evolution of 18F-FDG uptake in patients with sALCL has not been reported. For tumors lacking 18F-FDG uptake, there is a diagnostic pitfall of underestimating the cancer stage and misjudgment of metastases. In the present case, the PET scan results were negative at diagnosis but disseminated 18F-FDG avid lesions were found at relapse. Biopsy of bone marrow and lymph nodes revealed the pathological features were identical to the original tumor at the time of diagnosis. In the wake of such evolutional change, physicians dealing with sALCL should be cautious in interpretation of PET/CT scans.