Alternating rabacfosadine and doxorubicin for treatment of naïve canine lymphoma.

The current standard of care treatment for canine lymphoma is a multi-agent, CHOP-based chemotherapy protocol. Single agent doxorubicin (DOX) is less burdensome; however, multi-agent chemotherapy protocols are often superior. The recently approved drug rabacfosadine (RAB, Tanovea) provides an attractive option for combination therapy with DOX, as both drugs demonstrate efficacy against lymphoma and possess different mechanisms of action. A previous study evaluating alternating RAB/DOX reported an overall response rate (ORR) of 84%, with a median progression-free survival time (PFS) of 194 days. The aim of this prospective trial was to evaluate the same protocol in an additional population of dogs. Fifty-nine dogs with treatment naïve lymphoma were enrolled. RAB (1.0 mg/kg IV) was alternated with DOX (30 mg/m2 IV) every 21 days for up to six total treatments (3 cycles). Response assessment and adverse event (AE) evaluation were performed every 21 days using VCOG criteria. The ORR was 93% (79% CR, 14% PR). The median time to maximal response was 21.5 days; median PFS was 199 days. T cell immunophenotype and lack of treatment response were predictive of inferior outcomes. AEs were mostly gastrointestinal. Six dogs developed presumed or confirmed pulmonary fibrosis; four were grade 5. One dog experienced grade 3 extravasation injury with RAB that resolved with supportive treatment. These data mirror those of the previously reported RAB/DOX study, and support the finding that alternating RAB/DOX is a reasonable treatment option for canine lymphoma.

Evaluation of clinical response and prognostic factors in canine multicentric lymphoma treated with first rescue therapy.

Despite an initial strong response in most dogs with multicentric lymphoma treated with chemotherapy, relapse remains common. There is no clearly superior first rescue protocol described either for resistant or relapsed canine multicentric lymphoma. The objectives of this study were to assess clinical response and outcomes for canine multicentric lymphoma treated with first rescue protocols. The secondary objective was to assess prognostic variables for dogs undergoing these protocols. This was a bi-institutional retrospective cohort study. Two hundred and sixty-five dogs were treated with first rescue chemotherapy, including anthracycline-based combination chemotherapy (CHOP-like, n = 50), nitrosourea alkylating agent-rich chemotherapy (n = 45), anthracycline-based or related compound chemotherapy (n = 34), or nitrosourea single-agent chemotherapy (n = 136). The overall median progression free survival time of first rescue protocol was 56.0 days (0-455 days). Important prognostic factors identified for first rescue protocol included the attainment of a complete response to the first rescue chemotherapy (p < .001), the use of a CHOP-like first rescue protocol (p = .009), duration of first remission (HR 0.997, p = .028), and if prednisolone was included in the first rescue protocol (HR 0.41, p = .003). Adverse events (AE) were common, with 81.1% of dogs experiencing at least one AE during first rescue chemotherapy. This study highlights the need for improved first rescue therapies to provide durable remission in canine resistant or relapsed lymphoma.

Stage Migration in Canine Multicentric Lymphoma: Impact of Diagnostic Techniques on Assessing Disease Extent.

BACKGROUND/AIM: Stage migration, a phenomenon triggered by technological advancements allowing more sensitive tumor spread detection, results in alterations in the distribution of cancer stages within a population. Canine multicentric lymphoma is staged I to V based on the affected anatomic site(s) and substage a or b depending on the presence of tumor-related clinical signs. The primary objective of this study was to assess the influence of various diagnostic techniques on staging accuracy and determine whether multiple staging methods lead to significant stage migration, impacting the reliability of disease stage assignments. MATERIALS AND METHODS: Dogs cytologically diagnosed with multicentric lymphoma were staged using four different staging methods (A-D): A (physical examination, hemogram, blood smear), B (A plus thoracic X-ray, abdominal ultrasound), C (B plus liver and spleen cytology) and D (C plus bone marrow cytology). RESULTS: Twenty-three dogs were enrolled: 16 females (70%) and seven males (30%). Regarding immunophenotype, 21 dogs (91.3%) were B-cell and two dogs (8.7%) were T-cell. Stage migration was observed between all staging methods. Between A and B, 12 animals migrated from stage III to stage IV. Between B and C, four animals migrated, three to a higher stage (stage III to IV) and one to a lower stage (stage IV to III). Between C and D, one animal migrated from stage IV to V. The differences between staging methods A and B were statistically significant (p≤0.001). CONCLUSION: Stage migration in canine multicentric lymphoma depends on the diagnostic methods used and reinforces the need to use standardized staging methods to avoid it.

Jaundice caused by primary common bile duct lymphoma of a cat.

A 10-year-old American Shorthair cat presented with anorexia and jaundice, and echogenic evaluation revealed diffuse thickening of the common bile duct (CBD) wall. An exploratory laparotomy was conducted, the lesion was evaluated as difficult to remove, and the cat was euthanized and autopsied. Histologically, round neoplastic cells proliferated in the mucosa of the CBD and infiltrated the hepatic lobe, pancreas, and duodenum. Immunohistochemistry revealed that the neoplastic cells were positive for cytoplasmic-CD3 and granzyme B, and TCR-gamma clonal rearrangement was detected. Based on these findings, the neoplasia was diagnosed as a primary CBD lymphoma originating from cytotoxic T or natural killer cells. To the best of our knowledge, this is the first reported case of feline primary CBD lymphoma. Although rare, lymphoma of the CBD should be considered in cats with jaundice and thickening of the CBD.

Spindle cell cutaneous epitheliotropic T-cell lymphoma in an American Bulldog.

An 8-year-old American Bulldog developed coalescing exophytic bulbous nodules that grew rapidly on the left pinna and a single cutaneous mass on the left flank. Histological examination of the pinnal biopsy by a diagnostic laboratory revealed a densely cellular neoplasm with haphazardly arranged round to spindle cells with high mitotic activity and epitheliotropism. The initial diagnosis was a poorly differentiated malignant neoplasm with differential diagnoses including melanoma, tumour of histiocytic origin and, less likely, a pleomorphic lymphoma. A panel of melanoma immunohistochemical markers and immunolabelling for CD18 were pursued. Neoplastic cells were immunopositive for CD18 but negative for Melan-A, PNL2, TRP-1 and TRP-2, suggestive of a histiocytic tumour or lymphoma. The left ear masses recurred, and more masses developed on the body. The pinnectomized ear was submitted to the University of Missouri Veterinary Medical Diagnostic Laboratory. Similar cells were seen and were immunolabelled for CD18 and CD3 but were immunonegative for SOX10, CD79a and CD20. PCR for antigen receptor rearrangements revealed a clonal rearrangement of T-cell receptor gamma. These findings enabled a final diagnosis of epitheliotropic T-cell lymphoma with spindle cell morphology. Lymphoma should be considered as a potential differential diagnosis for cutaneous nodules of spindle cell morphology and lymphocytic immunohistochemical markers should be included in diagnostic panels.

Myeloid derived suppressor cells in peripheral blood can be a prognostic factor in canine transitional cell carcinoma.

Myeloid-derived suppressor cells (MDSCs) are immature cells with immunosuppressive properties found in the tumor microenvironment. MDSCs are divided into two major subsets: polymorphonuclear MDSCs (PMN-MDSCs) and monocytic MDSCs (M-MDSCs). Both MDSC subsets contribute to the creation of an immunosuppressive environment for tumor progression. In humans, patients with high levels of MDSCs show worse outcomes for several types of cancers. However, the association between MDSCs and clinical features has rarely been investigated in canine studies. In the present study, we measured the proportion of PMN-MDSCs and M-MDSCs in the peripheral blood and tumor tissue of dogs with hepatocellular carcinoma (HCC), prostate cancer (PC), transitional cell carcinoma (TCC), lymphoma, and pulmonary adenocarcinoma. Additionally, we examined immunosuppressive ability of PMN-MDSCs and M-MDSCs in peripheral blood mononuclear cells of TCC case on CD4+, CD8+ and interferon-γ+ cells and investigated the relationships of MDSCs with clinical features and outcomes. PMN-MDSCs increased in HCC, PC, TCC, and lymphoma. In contrast, M-MDSCs increased in the TCC. Both PMN-MDSCs and M-MDSCs exhibited immunosuppressive effects on CD8+, CD4+ and interferon-γ+ cells. In dogs with TCC, lymph node metastasis was associated with high level of PMN-MDSCs but not with M-MDSCs. High levels of both PMN-MDSCs and M-MDSCs were related to advanced tumor stage. Kaplan-Meier analysis revealed that high levels of both PMN-MDSCs and M-MDSCs were significantly associated with shorter overall survival. In addition, the Cox proportional hazard regression model showed that M-MDSCs and the tumor stage were independent prognostic factors for TCC. These results suggest that PMN-MDSCs and M-MDSCs may be involved in tumor progression and could be prognostic factors and promising therapeutic targets in dogs with TCC.

In vitro chemosensitivity testing of the feline large granular lymphocyte cell line (S87).

BACKGROUND: Feline large granular lymphocyte (LGL) lymphoma is an aggressive neoplasia characterised by short survival and poor response to chemotherapy. OBJECTIVES: In this study, the effect of different chemotherapeutic agents on the growth kinetics of the feline cell line S87, a non-MHC-restricted feline LGL cell line, was investigated. Where possible, IC50 (inhibitory concentration 50) values were determined. The IC50 values of the cell line as lymphoma models can provide clues to the situation in vivo and serve as a basis for studying resistance mechanisms. METHODS: Cells were incubated with various concentrations of vincristine, doxorubicin, 4-hydroperoxycyclophosphamide, prednisolone, methotrexate and L-asparaginase for 24 and 48 h, respectively. RESULTS: The IC50 values could be determined as 14.57 (7.49-28.32) µg/mL at 24 h incubation and 5.72 (4.05-8.07) µg/mL at 48 h incubation for doxorubicin and 9.12 (7.72-10.76) µg/mL at 24 h incubation and 4.53 (3.74-5.47) µg/mL at 48 h incubation for 4-hydroperpoxycyclophosphamide. Treatment with vincristine and methotrexate resulted in relatively high cell resistance whereas L-asparaginase and prednisolone treatment led to a reduction in cell number compared to control while cell viability was not affected (cytostatic effect). CONCLUSION: Overall, the feline LGL cell line S87 proves to be relatively sensitive to doxorubicin and 4-hydroperoxycyclophosphamide and relatively resistant to treatment with vincristine, prednisolone, methotrexate and L-asparaginase. The results of this study can be used for further investigations on resistance mechanisms in feline LGL lymphoma. Doxorubicin and cyclophosphamide can be interpreted as promising candidates for the therapy of feline LGL lymphomas.

Assessment of Y chromosome copy number alterations in non-neoplastic and neoplastic leukocytes of male dogs.

The loss of the Y chromosome (ChrY), also known as LOY, is a common genetic alteration observed in men. It occurs in non-neoplastic cells as an age-related change as well as in neoplastic cells of various cancer types. While well-documented in humans, LOY has not been extensively studied in non-human mammals. In this study, we developed simple digital PCR-based assays to assess the copy number of ChrY relative to the X chromosome (ChrX) and chromosome 8 (Chr8) to evaluate ChrY numerical alterations in male canine DNA specimens. Using these assays, we analyzed non-neoplastic leukocytes from 162 male dogs without hematopoietic neoplasia to investigate the occurrence of age-related LOY in non-neoplastic leukocytes. Additionally, we examined 101 tumor DNA specimens obtained from male dogs diagnosed with various types of lymphoma and leukemia to determine whether copy number alterations of the ChrY occur in canine hematopoietic cancers. Analysis of the 162 non-neoplastic leukocyte DNA specimens from male dogs of varying ages revealed a consistent ∼1:1 ChrY:ChrX ratio. This suggests that age-related LOY in non-neoplastic leukocytes is rare or absent in dogs. Conversely, a decreased or increased ChrY:ChrX ratio was detected in canine neoplastic leukocytes at varying frequencies across different canine hematopoietic malignancies (P = 0.01, Fisher's exact test). Notably, a higher incidence of LOY was observed in more aggressive cancer types. To determine if this relative LOY to ChrX was caused by changes in ChrY or ChrX, we further analyzed their relative copy numbers using Chr8 as a reference. Loss of ChrX relative to Chr8 was found in 21% (9/41) of B-cell lymphomas and 6% (1/18) of non-T-zone/high-grade T-cell lymphomas. In contrast, a subset (29%, 4/14) of T-cell chronic lymphocytic leukemia showed gain of ChrX relative to Chr8. Notably, no relative LOY to Chr8 was detected indolent hematopoietic cancers such as T-zone lymphoma (0/9) and chronic lymphocytic leukemia of B-cell (0/11) and T-cell origins (0/14). However, relative LOY to Chr8 was present in more aggressive canine hematopoietic cancers, with incidences of 24% (10/41) in B-cell lymphoma, 44% (8/18) in non-T-zone/high-grade T-cell lymphoma, and 75% (6/8) in acute leukemia. This study highlights both similarities and differences in LOY between human and canine non-neoplastic and neoplastic leukocytes. It underscores the need for further research into the role of ChrY in canine health and disease, as well as the significance of LOY across various species.

Spinal lymphoma in a goat.

A 3-year-old Pygmy Wether was presented for chronic hindlimb paralysis. A neurological exam revealed nonambulatory paraplegia with absent deep pain nociception, lack of hindlimb withdrawal reflexes, and paraspinal pain on palpation with T3 to L3 neurolocalization. MRI of the lumbar spine revealed an extensive, dorsal to dorsolateral, severely compressive, heterogeneously contrast-enhancing extradural lesion of the lumbar spine with intervertebral foraminal extension into the surrounding paraspinal musculature. Vertebral bone marrow involvement was also noted in the L5 and L6 vertebrae. A diagnosis of lymphoma was obtained after cytological sampling. This is the first case report describing specific MRI findings (signal characteristics, enhancement pattern, and perilesional changes) in a goat with paraspinal lymphoma.

Feline high-grade and large granular lymphocyte alimentary lymphomas treated with COP- or CHOP-based chemotherapy: A multi-centric retrospective study of 57 cases.

Specific data regarding outcome of cats with high-grade and large granular lymphocyte alimentary lymphoma (HGAL and LGL, respectively) treated with multi-agent chemotherapy are scarce. The aims of this multi-centric, retrospective study were to describe the outcome of cats with HGAL and LGL treated with COP- or CHOP-based chemotherapy and to identify potential prognostic factors. Cats with a cytological or histological diagnosis of HGAL or LGL lymphoma treated with COP- or CHOP-based protocol as first-line chemotherapy were included. Data regarding diagnosis, staging, treatment and follow-up were collected. Fifty-seven cats treated with CHOP (n = 37) or COP (n = 20) protocols were included. Complete response (CR), partial response (PR), stable disease (SD) and progressive disease (PD) were observed in 20%, 22%, 36% and 22% of cats, respectively, for an overall response rate of 42%. Median progression-free interval (PFI) was 148 days and overall median survival time (OST) was 131 days. Cats achieving CR, PR or SD showed significantly longer PFI (p < .01) and OST (p < .015) compared with cats with PD. Other positive prognostic factors in multi-variate analysis were rescue treatment (p < .001) and absence of lymph node involvement (p < .03). Negative prognostic factors were diffuse infiltration of the gastrointestinal tract (p = .035) and infiltration of a non-haematopoietic organ (p < .01).

Multicentric lymphoma in a donkey with intestinal and bone marrow involvement.

BACKGROUND: Lymphoma is a common neoplasm in horses but is reported much less commonly in donkeys. In this case report, we describe the macroscopic, microscopic and immunohistochemical features of a multicentric lymphoma with intestinal and bone marrow involvement. CASE PRESENTATION: A geriatric female donkey with history of chronic lameness was found dead. Post-mortem examination revealed advanced emaciation, periodontal disease, left front foot laminitis and multiple, soft, white to yellow tan intestinal transmural masses, up to 12 cm in diameter. Cytology suggested a round cell intestinal neoplasm. The femur of the left hint limb was double the size of the normal contralateral, with suspected neoplastic infiltration and replacement of bone marrow and bone. Histologically we diagnosed a lymphoma in the intestine and left femur. Immunohistochemically, the neoplastic cells showed CD3 immunolabelling, supporting a diagnosis of a multicentric T-cell lymphoma. CONCLUSIONS: To the authors' knowledge, this is the first time multicentric lymphoma is diagnosed in donkeys. Further studies of the genetic background, clinical, laboratory, histopathologic, and immunohistochemical, as well as the pathogenesis of lymphoma, is needed to better understand the uniquely low frequency of this neoplasm in donkeys.

Novel Treatments for Lymphoma.

Lymphoma is a common disease in companion animals. While conventional chemotherapy has the potential to induce remission and prolong life, relapse is common and novel treatments are needed to improve outcome. This review discusses recent modifications/adjustments to conventional standard of care therapy for canine and feline lymphoma, options for treatment or relapsed/refractory disease, and cutting-edge immunotherapy and small molecule-based approaches that are in varying stages of regulatory approval.

Unexpected diagnosis of canine lymphoma when performing an ultrasound-guided cystocentesis on a 3-year-old Rottweiler dog.

A 3-year-old spayed female Rottweiler dog was brought to a veterinary clinic because of weakness, lethargy, and hair coat changes. Hematology and clinical chemistry assessments revealed anemia, hypoalbuminemia, hyperglobulinemia, and hypothyroid. After persistent pyuria, an ultrasound-guided cystocentesis was completed, which revealed a large abdominal mass. A presumptive diagnosis of canine lymphoma with renal spread was made. Due to a poor prognosis, the dog was euthanized.

Diagnostic inattendu de lymphome canin lors de la réalisation d'une cystocentèse échoguidée sur un chien Rottweiler de 3 ans. Une chienne Rottweiler stérilisée de 3 ans a été amenée dans une clinique vétérinaire en raison de faiblesse, de léthargie et de changements de pelage. Les évaluations hématologiques et chimiques cliniques ont révélé une anémie, une hypoalbuminémie, une hyperglobulinémie et une hypothyroïdie. Après une pyurie persistante, une cystocentèse échoguidée a été réalisée, révélant une masse abdominale volumineuse. Un diagnostic présomptif de lymphome canin à propagation rénale a été posé. En raison d'un mauvais pronostic, le chien a été euthanasié.(Traduit par Dr Serge Messier).

Sonographic and computed tomographic features of intestinal mast cell tumors mimicking alimentary lymphoma in 2 dogs.

Two shih tzu dogs were referred to our clinic because of hematochezia and vomiting. Abdominal ultrasonography revealed a focal, asymmetric, exophytic small intestinal mass with loss of wall layering and muscular layer thickening of the adjacent intestine. Computed tomography (CT) in both dogs revealed a focal, asymmetric, homogenously contrast-enhanced exophytic jejunal and duodenal mass with an intact mucosal layer and generalized lymphadenopathy. Metastasis and ulceration were not detected on CT. The initial imaging diagnosis was lymphoma in both dogs; however, histopathological examination revealed the presence of intestinal mast cell tumors (iMCTs). Despite its similarity to alimentary lymphoma, iMCT should be considered a possible diagnosis, based on imaging characteristics, to ensure that proper treatments are selected. This is the first veterinary report describing detailed ultrasonographic and CT characteristics of iMCTs. Key clinical message: This is the first veterinary case report demonstrating sonographic and computed tomographic features of canine iMCT, which can be misdiagnosed as alimentary lymphoma. This report provides another differential diagnosis to consider when determining the appropriate patient treatment direction and histopathological examination.

Caractéristiques échographiques et tomodensitométriques de mastocytomes intestinaux imitant un lymphome alimentaire chez 2 chiens. Deux chiens shih tzu ont été référés à notre clinique en raison d'une hématochézie et de vomissements. L'échographie abdominale a révélé une masse focale, asymétrique et exophytique de l'intestin grêle avec perte de stratification pariétale et épaississement de la couche musculaire de l'intestin adjacent. La tomodensitométrie (TDM) chez les deux chiens a révélé une masse jéjunale et duodénale exophytique focale, asymétrique, homogène et contrastée avec une couche muqueuse intacte et une lymphadénopathie généralisée. Les métastases et les ulcérations n'ont pas été détectées par TDM. Le diagnostic initial d'imagerie était un lymphome chez les deux chiens; cependant, l'examen histopathologique a révélé la présence de mastocytomes intestinaux (iMCT). Malgré sa similitude avec le lymphome alimentaire, l'iMCT doit être considérée comme un diagnostic possible, basé sur les caractéristiques de l'imagerie, afin de garantir la sélection des traitements appropriés. Il s'agit du premier rapport vétérinaire décrivant les caractéristiques échographiques et tomodensitométriques détaillées des iMCT.Message clinique clé :Il s'agit du premier rapport de cas vétérinaire démontrant les caractéristiques échographiques et tomodensitométriques de l'iMCT canin, qui peuvent être diagnostiquées à tort comme un lymphome alimentaire. Ce rapport fournit un autre diagnostic différentiel à prendre en compte lors de la détermination de l'orientation thérapeutique et de l'examen histopathologique appropriés du patient.(Traduit par Dr Serge Messier).

Multiple myeloma in dogs: Use of the cell block technique as a new diagnostic tool.

BACKGROUND: The diagnosis of multiple myeloma (MM) in dogs may be challenging and complex. The cell blocks are a diagnostic technique that allows the characterization of neoplastic cells and, therefore, might help in the diagnosis of atypical MM. OBJECTIVE: The objective of the present work is to describe three clinical cases in which the cell blocks and immunohistochemistry contributed to the definitive diagnosis of canine MM. METHODS: Three dogs, one female and two males, with different clinical signs, were presented for consultation with anemia, hyperproteinemia with monoclonal gammopathy, and the presence of plasmacytosis in the bone marrow. Cytologic analysis of the spleen was performed in two dogs and was suggestive of the presence of lymphocytes or plasma cells of a neoplastic nature in one of the cases and plasma cell hyperplasia associated with extramedullary hematopoiesis in the other. Given the hypotheses of lymphoid neoplasms with a plasma cell phenotype, cell blocks from aspiration punctures were performed for immunohistochemical analysis with anti-CD3, CD20, CD79αcy, PAX5, and MUM1 antibodies. RESULTS: The results revealed positive staining for MUM1 in 80% of the cells in the spleen cell block and for CD20 and MUM1 in 70% of the cells in the bone marrow cell blocks, with negative staining for the other antibodies. The immunophenotyping results allowed the diagnosis of MM in the three cases and excluded other lymphoid neoplasms. CONCLUSIONS: This work reinforces the importance of using cell blocks in the diagnosis of neoplasms by demonstrating their potential to aid the diagnosis of MM.

Plasma cell-free DNA in canine lymphoma patients as a novel material for genotyping.

Canine lymphoma is a disease with high morbidity and poor long-term prognosis, despite a high response rate to chemotherapy. In this study, we focused on liquid biopsy, in which small amounts of substances from body fluids were analysed, to determine whether cell-free DNA (cfDNA) in the plasma can be used as a biomarker for lymphoma in dogs. We found that 23 patients with lymphoma had significantly higher cfDNA concentrations than the 12 healthy dogs (median 2360 ng/mL versus 299 ng/mL, p < .0001). Polymerase chain reaction for antigen receptor rearrangement (PARR) was also employed using cfDNA from the lymphoma group to investigate whether cfDNA could be used for the detection of genetic clonality of lymphomas, as well as the genomic DNA (gDNA) extracted from an original lesion in each case. The correlation of the PARR results between cfDNA and gDNA was observed in 100% of B-cell lymphomas (10/10), 77.8% of T-cell lymphomas (7/9), and 100% of other types of lymphomas (4/4), respectively. These results indicate that plasma cfDNA levels are increasing in canine lymphoma patients, that cfDNA concentration can be a novel diagnostic tool, and that it can be used as a diagnostic tool for PARR.

Domestic Cat Hepadnavirus Antigens in Lymphoma Tissues. Comment on Beatty et al. Domestic Cat Hepadnavirus and Lymphoma. Viruses 2023, 15, 2294.

We are addressing the comments made by Beatty et al [...].

Reply to Piewbang et al. Domestic Cat Hepadnavirus Antigens in Lymphoma Tissues. Comment on "Beatty et al. Domestic Cat Hepadnavirus and Lymphoma. Viruses 2023, 15, 2294".

We are grateful to the authors for providing additional data to demonstrate the presence of domestic cat hepadnavirus in lymphoma tissues [...].

Retrospective Evaluation of Melphalan, Vincristine, and Cytarabine Chemotherapy for the Treatment of Relapsed Canine Lymphoma.

Dogs diagnosed with multicentric lymphoma often relapse following induction therapy within the first year of treatment. The primary aim of this study was to evaluate the tolerability of a novel drug combination using melphalan, vincristine, and cytarabine (MOC) for the treatment of relapsed lymphoma. On day 1, dogs were treated with vincristine (0.5-0.6 mg/m2 IV) and cytarabine (300 mg/m2 IV over 4-6 hr or subcutaneously over 2 days). On day 7, dogs were treated with melphalan (20 mg/m2per os). This 2 wk protocol was repeated for at least three cycles or until treatment failure. Twenty-six dogs were treated with MOC and met the inclusion criteria. Twenty-three dogs had toxicity data, and all experienced adverse events with the majority graded as mild. The overall response rate was 38%, which included 19% of dogs who achieved a complete response. The median progression-free survival was 29 days (range 1-280 days). The overall clinical benefit was 65% for a median of 37 days (range 33-280 days). MOC is a safe treatment option for relapsed lymphoma in dogs.

Effect of proteasome inhibitors on canine lymphoma cell response to CHOP chemotherapy in vitro.

The standard treatment for canine lymphoma is the CHOP chemotherapy regimen. Proteasome inhibitors have been employed with CHOP for the treatment of human haematological malignancies but remain to be fully explored in canine lymphoma. We identified an association between poor response to CHOP chemotherapy and high mRNA expression levels of proteasomal subunits in a cohort of 15 canine lymphoma patients, and sought to determine the effect of proteasome inhibitors on the viability of a canine B-cell lymphoma cell line (CLBL-1). The aim of this study was to investigate whether proteasome inhibitors sensitize these cells to the CHOP agents doxorubicin, vincristine and cyclophosphamide (as 4-hydroxycyclophosphamide/4-HC). CLBL-1 cells were sensitive to proteasome inhibition by bortezomib and ixazomib. The IC50 of bortezomib was 15.1 nM and of ixazomib was 59.14 nM. Proteasome inhibitors plus doxorubicin had a synergistic effect on CLBL-1 viability; proteosome inhibitors plus vincristine showed different effects depending on the combination ratio, and there was an antagonistic effect with 4-HC. These results may have clinical utility, as proteasome inhibition could potentially be used with a synergizing CHOP compound to improve responsiveness to chemotherapy for canine lymphoma patients.