Metronomic chemotherapy (MC) represents an emerging strategy in veterinary oncology which involves the continuous or regularly scheduled administration of low-dose chemotherapeutic agents. Unlike conventional protocols known as maximum tolerated dose chemotherapy (MTDC), MC aims to inhibit tumor angiogenesis, stimulate antitumor immune responses, and delay or prevent the emergence of drug resistance. This review is structured into three key sections: the mechanisms of action of MC; its clinical indications in dogs and cats, particularly for advanced or treatment-resistant cancers; and reported outcomes regarding efficacy, safety, and tolerability. Additionally, we explore the growing interest in combining MC with other therapies, as well as the challenges and future directions for optimizing its use. Current evidence suggests that MC is a promising and well-tolerated option for managing various malignancies—such as carcinomas, sarcomas, and hemangiosarcomas—especially in patients who are not candidates for MTDC.

Serum lactate dehydrogenase (LDH) is a recognized prognostic biomarker in human lymphomas, yet its clinical significance in canine lymphoma remains insufficiently characterized. This study aimed to quantify serum LDH levels in healthy dogs and dogs with high-grade multicentric lymphoma (ML) (predominantly B-cell) and to investigate correlations between LDH levels and established clinical and laboratory prognostic indicators. Twenty-seven dogs were prospectively enrolled: healthy controls (G1, n = 7) and dogs with high-grade ML (G2, n = 20). Immunophenotyping was performed by immunohistochemistry (CD3/CD79a). LDH concentrations were measured at diagnosis (T0) and after six weeks of CHOP-based induction chemotherapy (T1). Statistical analyses included Kruskal–Wallis, Wilcoxon signed-rank, Pearson’s correlation, and mixed-effects models. Dogs with high-grade ML exhibited significantly elevated LDH levels compared to controls (median 545.5 U/L, range: 288.2–2816 U/L vs. 143 U/L, range: 66–272; p < 0.001). Dogs with thrombocytopenia had higher baseline LDH (median 746 U/L, range: 612–921; p = 0.006) and greater reductions following chemotherapy (median −1011.7 U/L, range: −159 to −2064; p = 0.004). LDH levels declined significantly after treatment (overall median reduction 50.7%; post-chemotherapy range: 60.4–752 U/L; n = 15; p = 0.013), with normalization achieved in 77.8% of dogs with complete response versus 16.7% with partial or progressive disease (p = 0.02). We confirmed that serum LDH is significantly elevated in dogs with high-grade ML and declines following effective chemotherapy, supporting its utility as a dynamic biomarker of tumor burden and treatment response. Thrombocytopenic dogs may represent a biologically distinct subset warranting further investigation.

Acute lymphoblastic leukemia (ALL) with double-negative T-cell phenotype (CD4-/CD8-) represents a rare presentation in dogs requiring flow cytometry for definitive diagnosis. An eight-year-old German Shepherd presented with progressive lethargy, weight loss, and severe cytopenias. Complete blood count (CBC) revealed severe leukocytosis (90,500/μL) with 99% atypical lymphocytes, non-regenerative anemia, and thrombocytopenia. While blood smear examination demonstrated lymphoblastic morphology, flow cytometry was essential to identify the aberrant immunophenotype CD3+/CD4-/CD8-/CD34+, confirming ALL with arrested differentiation at the earliest T-cell stage. Palliative chemotherapy produced minimal response, and the patient died 11 days post-diagnosis. Flow cytometry results were received 5 days post-mortem, highlighting challenges in turnaround time for specialized diagnostics. This case emphasizes that flow cytometry is essential for accurate diagnosis of acute leukemia with aberrant phenotypes and underscores the need for rapid immunophenotyping services to enable timely therapeutic intervention.

Background/Objectives: Intranasal tumors are common malignancies in dogs, characterized by locally aggressive behavior and clinical signs such as epistaxis, nasal discharge, and facial deformity. Radiotherapy (RT) is considered the treatment of choice due to anatomical limitations to surgical resection. This study aimed to evaluate clinical outcomes, toxicity, and prognostic factors in dogs with primary malignant intranasal tumors treated with cobalt-60–based megavoltage radiotherapy. Methods: This retrospective study included 40 dogs with histopathologically confirmed primary malignant intranasal tumors treated between September 2018 and February 2025 at a veterinary radiotherapy clinic in Rio de Janeiro, Brazil. Medical records were reviewed for patient demographics, tumor characteristics, treatment protocols, response, toxicity, and survival outcomes. Tumors were staged using modified Adams criteria based on computed tomography. Definitive-intent protocols (n = 32) delivered 48–54 Gy in 10–13 fractions administered three to five times weekly, while palliative protocols consisted of either four fractions of 8 Gy delivered once weekly or five fractions of 4 Gy delivered daily. Results: Adenocarcinoma was the most common histologic subtype (42.5%), and 82.5% of dogs had stage III–IV disease. The objective response rate was 82.5% (CR: 17.5%; PR: 65.0%), with clinical benefit observed in 92.5% of cases. Acute toxicity was frequent but manageable, primarily affecting skin, oral mucosa, and eyes. Overall median progression-free interval (PFI) and survival time (MST) were 382 days and 430 days, respectively. Stage IV disease was significantly associated with shorter survival when compared to stage I-III (MST 345 vs. 1063 days, respectively; p = 0.016). Treatment response was significantly associated with PFI in univariate analysis (p < 0.05). Conclusions: Radiotherapy provided high response rates and meaningful clinical benefit with acceptable toxicity in dogs with malignant intranasal tumors, highlighting the importance of early diagnosis and treatment. Further prospective studies with standardized protocols are warranted.

Monoclonal gammopathy (MG) is rare in dogs and multiple myeloma (MM) is its main cause. This study reports the case of a female dog which presented MG associated with a MM and consequent blood hyperviscosity syndrome (HVS). Patient presented systemic hypertension, renal disease, chorioretinitis and secondary glaucoma due to HVS. Serological tests for leishmaniasis and for ehrlichiosis demonstrated negative and score 4 from 5, respectively. Non-regenerative anemia, thrombocytopenia, hyperproteinemia, hypoalbuminemia, hyperglobulinemia, creatinine and blood urea nitrogen (BUN) increases, hypercalcemia, hyperphosphatemia, proteinuria, decreased urinary density, and monoclonal peak of gamma globulins were observed. First myelogram identified 81% of medullary plasmacytosis which suggested MM. Plasmapheresis and chemotherapy with melphalan and prednisolone were performed with positive results. The treatment was effective with complete remission of HVS signs, medullary plasmocytosis reduction (21,8%) and malignant criteria decrease, as well as neoplastic control.

Objetivou-se, com este trabalho, abordar os principais métodos diagnósticos, critérios de estadiamento e subestadiamento, bem como as opções terapêuticas e o prognóstico do linfoma multicêntrico canino (LMC). O LMC é uma das neoplasias hematopoiéticas mais frequentes em cães, estimativas variam entre 7–24% de todas as neoplasias caninas e aproximadamente 85% das neoplasias hematopoiéticas. Trata-se de uma afecção de origem linfoide, caracterizada pela proliferação descontrolada de linfócitos em diferentes estágios de diferenciação, com etiologia multifatorial que envolve predisposição genética, fatores ambientais e imunossupressão. A classificação baseia-se em critérios clínicos, histológicos e imunofenotípicos, sendo a forma multicêntrica a apresentação clínica mais comum. O diagnóstico envolve a associação de exames clínicos, citopatológicos, histopatológicos e de biologia molecular. O estadiamento avalia a extensão da doença, enquanto o subestadiamento considera a presença ou ausência de sinais clínicos sistêmicos. A poliquimioterapia, especialmente o protocolo CHOP de 19 semanas, constitui o tratamento de primeira escolha. Conclui-se que o linfoma multicêntrico canino exige diagnóstico preciso e abordagem terapêutica individualizada, visando à maximização da sobrevida e à manutenção da qualidade de vida dos pacientes.