Descriptive analysis and prognostic factors in cats with myeloma‐related disorders: A multicenter retrospective study of 50 cases

Abstract Background Myeloma‐related disorders (MRDs) are rare and poorly documented neoplasms of cats. Hypothesis/Objectives To describe clinical, clinicopathologic, and imaging findings, response to treatment, and survival time and to identify factors associated with shorter outcomes in cats with MRD. Animals Fifty cats with a diagnosis of MRD. Methods Cats with paraproteinemia confirmed by serum protein electrophoresis (SPE) and either intramedullary plasmacytosis >10%, marked cytonuclear atypia with intramedullary plasmacytosis that ranged between 5% and 10%, or cytologically or histologically confirmed visceral infiltration were retrospectively included from several veterinary referral centers. Results Bone marrow plasmacytosis and splenic or hepatic involvement were present in 17/27 cats (63%), 36/42 cats (86%), and 27/38 cats (71%), respectively. Anemia was reported in 33/49 cats (67%) and thrombocytopenia in 16/47 cats (34%). Some of the treatments that the cats received included melphalan and prednisolone (n = 19), cyclophosphamide and prednisolone (n = 10), chlorambucil and prednisolone (n = 4), prednisolone (n = 4), or other (n = 4). The overall response rates to melphalan, cyclophosphamide, and chlorambucil in combination with prednisolone were 87%, 90%, and 100%, respectively. Adverse events to melphalan or cyclophosphamide occurred in 65% and 23% of cats, respectively. Median survival time was 122 days (range, 0‐1403) and was not significantly associated with chemotherapy protocol. Anemia (hazard ratio [HR], 3.1; 95% confidence interval [CI], 1.0‐9.8) and thrombocytopenia (HR, 2.7; 95% CI, 1.2‐6.0) were risk factors for shorter survival. Conclusions and Clinical Importance Our study confirmed the guarded prognosis of MRD in cats and identified risk factors for shorter survival times.