Myeloma‐Related Disorders in Cats Commonly Present as Extramedullary Neoplasms in Contrast to Myeloma in Human Patients: 24 Cases with Clinical Follow‐up

Abstract

Radiographic bone lesions are uncommon in cats with MRD and extramedullary presentation is common, relative to human myeloma.

Histopathologic, Immunohistochemical, and Cytologic Analysis of Feline Myeloma-Related Disorders: Further Evidence for Primary Extramedullary Development in the Cat

“…We previously reported that marked extramedullary involvement at initial clinical presentation is significantly more common in cats than in human MRD patients (67% versus ,5%, P , 0.001). 49 In the current report, we demonstrate that cats with well-differentiated tumors more commonly have extramedullary involvement than human patients with well-differentiated tumors (90% versus 20%, P , 0.0002). The multistep transformation model of human myeloma hypothesizes that the neoplastic transformation of a well-differentiated myeloma cell occurs primarily in the intramedullary compartment, and, over time, the neoplasm evolves a poorly differentiated (plasmablastic) morphology and extramedullary metastases.…”

“…Signalment, historical, clinical, clinicopathologic, and imaging features, as well as response to treatment for 24 of these confirmed cases, have been reported elsewhere. 49 …”

“…8,48,53 Historically, feline MRD has been assumed to resemble human myeloma with intramedullary involvement as a key diagnostic feature. 16,29,39,45,54 However, we and others have recently reported that extramedullary involvement is more common at initial presentation in feline than in human MRD (67% versus ,5%, P , 0.001), 49 and systemic effects and malignant neoplastic behavior are common in both cutaneous and noncutaneous feline extramedullary plasmacytomas (EMP). 10,17,30,39,49,54,59,66 It is unknown whether feline MRD with extramedullary involvement commonly arise from the extramedullary compartment or metastasize from the intramedullary compartment.…”

“…33 Since then, a diverse array of sometimes confusing terminology and diagnostic criteria have been used for feline MRD, including multiple myeloma, lymphoma, plasmacytoid lymphosarcoma, plasma cell dyscrasia, plasmacytoma, plasma cell sarcoma, and plasma cell tumor. 18,20,30,51,52,62,77 In a previous report, 49 we classified reported feline MRD in the following diagnostic categories: 1) myeloma (intramedullary or combined intra-and extramedullary involvement), 49 2) cutaneous extramedullary plasmacytoma (CEMP), 49 3) noncutaneous extramedullary plasmacytoma (NCEMP), 49 4) solitary plasmacytoma of bone (SPB), 50 5) IgM (Waldenströ m's) macroglobulinemia, 45,77 6) immunoglobulin secreting lymphoma (IgSL), 17 and 7) myeloma cell leukemia. 19,54,59 Few publications describe the cytologic or histologic features of feline MRD.…”

“…79 We have previously reported that marked extramedullary involvement at initial clinical presentation is significantly more common in the cat than in human patients (67% versus ,5%, P , 0.001). 49 In the current study, our a priori hypotheses were 1) that tumor category predicts survival and 2) that cats with well-differentiated tumors more often have extramedullary involvement than do human patients with well-differentiated tumors.…”