Postchemotherapy Histiocyte-rich Pseudotumor Mimicking Residual Lymphoma: A Report of 11 Cases Correlating Clinicopathologic and Radiologic Findings.

Postchemotherapy histiocyte-rich pseudotumor is a rare event in lymphoma patients and can cause elevated metabolic activity on positron emission tomography-computed tomography scan mimicking residual tumor. Here, we reported 11 lymphoma cases showing mass-like lesions with increased fluorodeoxyglucose uptake after chemotherapy. These postchemotherapy lesions occurred in various anatomic sites including spleen, mediastinum, lymph node, and other tissue locations, concerning for refractory or residual lymphoma. Their median size was 2.7 cm (range, 1.4 to 7.7 cm) and the median standardized uptake value on positron emission tomography-computed tomography was 10.6 (range, 5.2 to 13.8). Histologic examination of these lesions demonstrated reactive changes mainly composed of histiocyte-rich proliferation without viable lymphoma. Fat necrosis, cholesterol cleft, and calcium deposit were also commonly observed. After biopsies, 3 patients received additional chemotherapy, 2 had stem cell transplant with adjuvant chemotherapy or radiation, 1 had surgical excision, and the remaining 5 patients did not receive any further treatment. Follow-up imaging studies showed the resolved or decreased fluorodeoxyglucose activities in all patients including those without additional treatments, consistent with benign/reactive nature of these pseudotumor lesions. This study illustrates postchemotherapy mass-like lesions with elevated metabolic activity do not always represent residual disease and provides awareness of correlation between radiologic and histologic features of these lesions to avoid misinterpretation and overtreatment of lymphoma patients after chemotherapy.