Therapy-Related Extamedullary Hematopoiesis: An Unexpected Finding and Diagnostic Pitfalls
Daniel B Wimmer, Eric Salazar, Arthur W Zieske, Wayne L Chandler, Mary R Schwartz. Methodist Hospital, Houston, TX
Background: Hematopoiesis is a complex process involving progressive differentiation of diverse cellular blood components. Advances in understanding how regulatory factors affect hematopoiesis have dramatically impacted the clinical management of patients with cytopenias. Manufactured therapeutic cytokines and their analogs are now commonly used to stimulate or augment hematopoiesis in order to restore physiologic levels of hematopoietic cells. While the role of therapeutic cytokines in medullary hematopoiesis is well-established, the impact of therapeutic cytokines on extramedullary hematopoiesis (EMH) is less clear. The exact incidence of extramedullary hematopoiesis is unknown, and the phenomenon is uncommonly identified in surgical pathology specimens. Without a high index of suspicion, megakaryocytes and hematopoietic progenitor cells may morphologically mimic certain malignancies, especially when tissue sampling is limited. To avoid potential diagnostic pitfalls pathologists should be aware of extrinsic factors that could influence extramedullary hematopoiesis.
Design: We performed a retrospective analysis of surgical, cytology, autopsy, and hematopathology specimens from five hospitals from 2007-2012. Records for 486,800 cases were screened.
Results: Sixty cases satisfied our search criteria for a diagnosis of EMH. We found that EMH occurred at a rate of 0.012% for all specimens. Medical records were available for review in 54 of the 60 patients with documented EMH. Of these, 21% had received or were currently receiving the therapeutic cytokines filgrastim or darbopoietin. An additional 11% of patients with EMH were receiving levothyroxine, a lesser known, but well-documented factor involved in hematopoiesis. Therefore, of the patients with EMH and available medical records, 32% were receiving or had recently received medical therapy that stimulates hematopoiesis.
Conclusions: To our knowledge, this is the largest retrospective study examining the relationship between extramedullary hematopoiesis and medical therapy. While further studies are needed to evaluate the overall incidence and direct relationship between hematopoietic-stimulating agents and EMH, pathologists should have a higher level of suspicion for EMH in patients receiving these therapies. The morphologic features of EMH in an unexpected setting may be a potential diagnostic pitfall leading to possible overinterpretion of malignancy or suspicion for malignancy. Increased awareness of the factors influencing EMH can prevent such pitfalls when differentiating benign EMH from malignant entities.
Wednesday, March 6, 2013 9:30 AM
Poster Session V # 220, Wednesday Morning