[P-14] Post-chemotherapy histiocyte-rich pseudotumour involving the pancreas

Thu D.A. Phan¹, Thao T.P. Ho², An T.T. Dao^2,3 and Hieu T. Le¹

1. Department of Pathology, Faculty of Medicine, University of Medicine and Pharmacy at Ho Chi Minh City, Ho Chi Minh City, Vietnam
2. Department of Haemato-Oncology, Children's Hospital 2, Ho Chi Minh City, Vietnam
3. Department of Paediatrics, Faculty of Medicine, University of Medicine and Pharmacy at Ho Chi Minh City, Ho Chi Minh City, Vietnam

Background: Histiocyte-rich pseudotumour (HPRT) developing post-chemoradiation therapy is a rare benign reaction. Although benign, it can clinically and radiologically mimic residual tumours or recurrent/relapsed disease, causing challenges in management.

Case Presentation: A 9-year-old boy presented with abdominal pain, weight loss for a week. CT scan revealed a solid, heterogeneous, ill-defined mass originated from the pancreas. We found the tumor invading the omentum and small intestine during surgery and resected these involved organs. The patient was diagnosed with Diffuse Large B-Cell Lymphoma (DLBCL), risk group B, and initiated chemotherapy based on LMB89 protocol. CT scan showed the incomplete response to treatment with the residual mass when the patient completed the first cycle of the third phase, so he was re-stratified into risk group C to initiate the other regimen. After the third phase, the patient underwent the second surgery to resect the pancreas tumour. The tumour exhibited a xanthogranulomatous appearance with central necrosis surrounded by loose oedematous fibrous tissue, numerous foamy macrophages, small lymphocytes, and no residual tumour cells. This pathological pattern was consistent with post-chemotherapy HPRT. The patient kept on receiving treatment with the LMB89 protocol at the maintenance phase.

Discussion and Conclusion: Despite sensitivity in assessing residual mass, a CT scan is less helpful in the differential diagnosis between residual tumour and necrotic mass. An excisional biopsy is of importance to confirm the diagnosis of post-chemotherapy HPRT and exclude other neoplasms. Awareness of this entity is needed to avoid misdiagnosis or overtreatment of the residual mass following chemotherapy.