Postchemotherapy Histiocyte-rich Pseudotumor Mimicking Residual Lymphoma

Abstract

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.

Resistance of B-Cell Lymphomas to CAR T-Cell Therapy Is Associated With Genomic Tumor Changes Which Can Result in Transdifferentiation

“…The histologic features at relapse were puzzling since they consisted of histiocytic cells without major atypia, arousing suspicion for a reactive process. Postchemotherapy histiocyte-rich pseudotumors have been recently reported in lymphoma patients, with indolent behavior and favorable outcome despite the elevated metabolic activity 32. In case #6, however, the rapid clinical progression and the clonal link evidenced by identical IGH rearrangements in both paired tumors supported the hypothesis of a lymphoma relapse with histiocytic transdifferentiation.…”