Suspected myelodysplastic/myeloproliferative neoplasm in a feline leukemia virus‐negative cat

Abstract

A 10-year-old castrated Domestic Short-Haired cat was presented to a primary care veterinarian for a wellness examination and laboratory examination for monitoring of diabetes mellitus. The CBC revealed marked thrombocytosis, leukopenia and macrocytic, normochromic anemia. The cat tested negative for FeLV and feline immunodeficiency virus, but was positive for Mycoplasma haemominutum by PCR. Hematologic abnormalities were not responsive to therapy, so a repeat CBC and a bone marrow aspiration for cytology were performed. Additional blood smear findings included anisocytosis with megaloblastic erythroid precursors, large platelets, eosinophilic myelocytes and metamyelocytes, and rare unidentified blasts. The bone marrow smear was highly cellular, and the cytologic pattern was consistent with myelodysplastic syndrome with an erythroid predominance. At that time, 15% blasts were present. The cat was treated with a vitamin K analog, doxycycline, and prednisolone, but without a clinical response. Within 3 months, euthanasia was elected due to declining quality of life, and a necropsy was performed. Postmortem bone marrow smears were highly cellular and dominated by monomorphic blasts of unknown line of origin (52%), persistent marked erythroid and megakaryocytic dysplasia, and ineffective erythropoiesis and granulopoiesis. Immunohistochemical, immunocytochemical, and cytochemical stains resulted in a diagnosis of acute myeloid leukemia of unclassified type. Additional histologic findings included mixed hepatitis with trematode infestation and lymphoplasmacytic interstitial nephritis with fibrosis. The marked thrombocytosis with myelodysplastic syndrome and the FeLV-negative status of this cat were unusual. The difficulty in classifying the myelodysplasia and subsequent leukemia highlights a need for further reporting and characterization of these types of disease.

A cat with myelodysplastic syndrome by administration of the methylation inhibitor Azacytidine

“…In fact, feline lymphoma has been reported to show a clearly poor prognosis in individuals infected with FeLV [3]. To date, almost all cases of MDS in cats involved FeLV infections, but outbreaks of FeLV-uninfected acute leukemia have been sporadically reported in recent years [4,26]. FeLV, an infectious agent that induces tumorigenesis, was not observed in this case, suggesting that the patient's prognosis may be favorable as a result.…”

“…To our knowledge, this report is the first showing long-term survival in feline MDS after the administration of AZA. A standard therapeutic regimen for feline MDS has not been reported to date because of the limited number of cases, which was less than 50 between 1990 and 2020 [2,8,11,23,24,26]. In fact, there have been no reports comparing the drug treatment effects in cats with AML and MDS with those in a control group, and the rarity of this disease is an obstacle to finding an effective treatment method.…”

“…There have been reports on the course of treatment in several cats with MDS [8,11,23,25]. In some previous reports, cats with MDS were treated with blood transfusion, antibiotics, prednisolone, cyclosporine, erythropoietin, menatetrenone [8,9,25,26]. Interestingly, in previous studies, cats with MDS that showed long survival periods after receiving cytarabine, which shows the same antimetabolite activity as AZA, which has differentiating and demethylating effects [8].…”

“…The cytopenic pathology of MDS is caused by clonal expansion of hematopoietic stem cells and their markedly reduced differentiation and maturation ability [10,15,16]. An effective therapeutic regimen for feline MDS has not been established, and most cats with MDS show leukemia progression, short survival duration and poor prognosis [8,[23][24][25][26]. In particular, our previous report demonstrated that the high-risk group of feline MDS classified into refractory anemia (RA) with excess of blasts (RAEB), RAEB in transformation (RAEB in T), and chronic myelomonocytic leukemia (CMMoL) based on the French-American-British (FAB) classification has a higher probability of transition to acute leukemia and a poorer prognosis than the low-risk groups, including the RA group, suggesting that RAEB is refractory to the therapies used so far [8,11,23,25].…”

“…In particular, our previous report demonstrated that the high-risk group of feline MDS classified into refractory anemia (RA) with excess of blasts (RAEB), RAEB in transformation (RAEB in T), and chronic myelomonocytic leukemia (CMMoL) based on the French-American-British (FAB) classification has a higher probability of transition to acute leukemia and a poorer prognosis than the low-risk groups, including the RA group, suggesting that RAEB is refractory to the therapies used so far [8,11,23,25]. In some previous reports, cats with MDS were treated with blood transfusion, antibiotics, prednisolone, cyclosporine, and erythropoietin [8,9,25,26]. These treatments were supportive therapies, since a detailed case report using chemotherapy has not been reported due to the small number of spontaneous cases of feline MDS.…”