Cardiac Rhabdomyoma in Four Göttingen Minipigs.

Göttingen minipigs are increasingly used as an alternative large animal model in nonclinical toxicology studies, and proliferative lesions in this species are rare. Here, we report four cases of cardiac rhabdomyoma in Göttingen minipigs, an incidental and benign mass in the heart. Three cases lacked gross observations and had a microscopic nodule in either the left ventricle or interventricular septum. The last case had a large, firm, raised nodule on a left ventricular papillary muscle noted at necropsy, with additional microscopic intramural masses in the left ventricular wall. In all cases, microscopic evaluation revealed well-circumscribed, expansile nodules composed of bundles of large, highly vacuolated, ovoid to polygonal cells with variable cytoplasmic processes radiating from a centrally located nucleus. Cells displayed patchy accumulation of intracytoplasmic, PAS-positive material and haphazardly arranged cytoplasmic cross-striations. There was no evidence of cardiac insufficiency or other data to suggest the masses were clinically meaningful. Cardiac rhabdomyomas have been reported in meat-hybrid swine, with a breed predisposition in red wattle. This lesion is well established in guinea pigs, but documentation in other laboratory species used in toxicologic studies is limited to two beagle dogs. To our knowledge, this is the first report of spontaneous cardiac rhabdomyoma in Göttingen minipigs.

Genomic landscapes of canine splenic angiosarcoma (hemangiosarcoma) contain extensive heterogeneity within and between patients.

Cancer genomic heterogeneity presents significant challenges for understanding oncogenic processes and for cancer's clinical management. Variation in driver mutation frequency between patients with the same tumor type as well as within an individual patients' cancer can shape the use of mutations as diagnostic, prognostic, and predictive biomarkers. We have characterized genomic heterogeneity between and within canine splenic hemangiosarcoma (HSA), a common naturally occurring cancer in pet dogs that is similar to human angiosarcoma (AS). HSA is a clinically, physiologically, and genomically complex canine cancer that may serve as a valuable model for understanding the origin and clinical impact of cancer heterogeneity. We conducted a prospective collection of 52 splenic masses from 43 dogs (27 HSA, 15 benign masses, and 1 stromal sarcoma) presenting for emergency care with hemoperitoneum secondary to a ruptured splenic mass. Multi-platform genomic analysis included matched tumor/normal targeted sequencing panel and exome sequencing. We found candidate somatic cancer driver mutations in 14/27 (52%) HSAs. Among recurrent candidate driver mutations, TP53 was most commonly mutated (30%) followed by PIK3CA (15%), AKT1 (11%), and CDKN2AIP (11%). We also identified significant intratumoral genomic heterogeneity, consistent with a branched evolution model, through multi-region exome sequencing of three distinct tumor regions from selected primary splenic tumors. These data provide new perspectives on the genomic landscape of this veterinary cancer and suggest a cross-species value for using HSA in pet dogs as a naturally occurring model of intratumoral heterogeneity.

Prospective clinical trial testing COXEN-based gene expression models of chemosensitivity in dogs with spontaneous osteosarcoma.

BACKGROUND: This study is a prospective clinical trial in dogs with osteosarcoma testing a gene expression model (GEM) predicting the chemosensitivity of tumors to carboplatin (CARBO) or doxorubicin (DOX) developed using the COXEN method. PATIENTS AND METHODS: Sixty dogs with appendicular osteosarcoma were enrolled in this trial. RNA isolation and gene expression profiling were conducted with 2 biopsies for 54/63 screened tumors, and with a single biopsy for 9 tumors. Resulting gene expression data were used for calculation of a COXEN score for CARBO and DOX based on a previous study showing the significance of this predictor on patient outcome utilizing retrospective data (BMC Bioinformatics 17:93). Dogs were assigned adjuvant CARBO, DOX or the combination based on the results of the COXEN score following surgical removal of the tumor via amputation and were monitored for disease progression by chest radiograph every 2 months. RESULTS: The COXEN predictor of chemosensitivity to CARBO or DOX was not a significant predictor of progression-free interval or overall survival for the trial participants. The calculation of DOX COXEN score using gene expression data from two independent biopsies of the same tumor were highly correlated (P < 0.0001), whereas the calculated CARBO COXEN score was not (P = 0.3039). CONCLUSION: The COXEN predictor of chemosensitivity to CARBO or DOX is not a significant predictor of outcome when utilized in this prospective study. This trial represents the first prospective trial of a GEM predictor of chemosensitivity and establishes pet dogs with cancer as viable surrogates for prospective trials of prognostic indicators.

Skull Base Primary Extracranial Meningioma with Hyperostosis in a Small Mixed-Breed Dog.

A 7 yr old female spayed Chihuahua-terrier mix was presented for a progressive dry, hacking cough over 9 mo, with dyspnea aggravated by eating and drinking. Computed tomography of the skull revealed a large mineral attenuating mass associated with the left skull base, without intracranial involvement. A modified ventral paramedian hypophysectomy approach along the medial aspect of the left ramus was used to approach the base of the skull. Ninety percent of the mass was debulked via high-speed pneumatic burr. Histopathology was consistent with hyperostosis originating from a primary extracranial meningioma (ECM), with the tissue staining positive for vimentin and negative for cytokeratin. The patient was symptom free for 9 mo before clinical signs returned because of tumor recurrence and was euthanized 11 mo postoperation because of diminished quality of life. ECM is uncommonly reported in the dog, and to the authors' knowledge has not previously been reported with hyperostosis or located along the skull base at the level of the tympanic bulla. Additionally, although hyperostosis predominantly occurs as diffuse bone thickening adjacent to a meningioma, proliferative focal hyperostosis is uncommon. Given the findings in this patient, ECM should be considered as a differential diagnosis for osseous skull base masses.

Role of Periostin Expression in Canine Osteosarcoma Biology and Clinical Outcome.

Periostin is a matricellular protein important in regulating bone, tooth, and cardiac development. In pathologic conditions, periostin drives allergic and fibrotic inflammatory diseases and is also overexpressed in certain cancers. Periostin signaling in tumors has been shown to promote angiogenesis, metastasis, and cancer stem cell survival in rodent models, and its overexpression is associated with poor prognosis in human glioblastoma. However, the role of periostin in regulating tumorigenesis of canine cancers has not been evaluated. Given its role in bone development, we sought to evaluate mRNA and protein expression of periostin in canine osteosarcoma (OS) and assess its association with patient outcome. We validated an anti-human periostin antibody cross-reactive to canine periostin via western blot and immunohistochemistry and evaluated periostin expression in microarray data from 49 primary canine OS tumors and 8 normal bone samples. Periostin mRNA was upregulated greater than 40-fold in canine OS tumors compared to normal bone and was significantly correlated with periostin protein expression based on quantitative image analysis. However, neither periostin mRNA nor protein expression were associated with time to metastasis in this cohort. Gene Set Enrichment Analysis demonstrated significant enhancement of pro-tumorigenic pathways including canonical WNT signaling, epithelial-mesenchymal transition, and angiogenesis in periostin-high tumors, while periostin-low tumors demonstrated evidence of heightened antitumor immune responses. Overall, these data identify a novel antibody that can be used as a tool for evaluation of periostin expression in dogs and suggest that investigation of Wnt pathway-targeted drugs in periostin overexpressing canine OS may be a potential therapeutic target.

Diffuse Small B-Cell Lymphoma: A High-Grade Malignancy.

The most common subtype of lymphoma in the dog is diffuse large B-cell lymphoma (DLBCL). The remaining forms of B-cell lymphoma in dogs are categorized as small-to-intermediate in size and include marginal zone, follicular, mantle cell, and small-cell lymphocytic lymphoma. Marginal zone lymphoma and follicular lymphoma have readily identifiable unique histologic features while other forms of small B-cell lymphoma in the dog are poorly described by histopathology. Forty-seven cases of nodal small B-cell lymphoma identified by flow cytometry (small cell size based on forward scatter) with concurrent histopathology were reviewed. These cases fell into 3 histologic subtypes: marginal zone lymphoma, follicular lymphoma, and a diffuse form of small B-cell lymphoma with consistent features. As a descriptive term, we refer to the latter subtype as diffuse small B-cell lymphoma (DSBCL) until it can be further characterized by gene expression profiling and other molecular tools. Clinical presentation of DSBCL was compared to cases of histologically confirmed DLBCL and clinical follow-up was obtained for 22 of the 27 cases of DSBCL. This subset of diffuse small B-cell lymphoma had an overall median survival of 140 days. The expression of CD21, class II MHC and CD25 by flow cytometry did not differ between DSBCL and the other histologic subtypes of small cell B-cell lymphoma making histopathology the only current method of classification.

Histological and mechanical comparisons of arytenoid cartilage between 4 brachycephalic and 8 non-brachycephalic dogs: A pilot study.

Brachycephalic airway syndrome (BAS) is a well-established cause of respiratory distress in dogs. BAS without surgical correction results in eventual laryngeal collapse. Arytenoid lateralization has been used to treat severe laryngeal collapse with some highly variable results. Chondromalacia and decreased stiffness of the arytenoid cartilage has been postulated a source of failure after arytenoid lateralization but no report of the histological characteristics and mechanical strength of arytenoid cartilage in brachycephalic dogs has been reported. Here we report histological and mechanical features in arytenoid cartilage of brachycephalic dogs. We identified the arytenoid cartilage in brachycephalic dogs presented degenerative histological characteristics and decreased load to failure and stiffness compared to that in non-brachycephalic dogs. Together, these observations suggest that degenerative condition of arytenoid cartilage in brachycephalic dogs could contribute to chondromalacia and mechanical weakness of arytenoid cartilage and result in cause of failure after arytenoid lateralization.

Unfolding the diagnosis of subspectacular fluid opacity in a corn snake (Pantherophis guttatus).

OBJECTIVE: To present the results of clinical, surgical, and histopathologic procedures and how these were compared with the initial presumptive clinical diagnosis in a corn snake (Pantherophis guttatus) presenting with subspectacular fluid opacity; and to improve upon currently established surgical enucleation techniques in the snake. ANIMAL STUDIED: An 8-month-old corn snake was presented for enlarged globe OD. PROCEDURES: The following diagnostics were performed: systemic and ophthalmic examinations, complete blood count, cytology and culture of subspectacular fluid, and histopathology of enucleated globe and spectacle. Enucleation was performed in a routine fashion with the addition of a porcine small intestinal submucosa bioscaffold graft (SISplus™; Avalon Medical, Stillwater, MN), sutured over the orbit. RESULTS: Systemic examination revealed signs of maxillary stomatitis. Ophthalmic examination revealed semitransparent fluid in the subspectacular space. Complete blood count was unremarkable. Cytology of fluid obtained via subspectacular centesis was acellular, and culture grew Clostridium perfringens, which was consistent with the clinical suspicion of right maxillary stomatitis. Histopathology of the enucleated globe revealed spectaculitis, characterized by regional heterophilic inflammation, and no evidence of lymph dissection in the (peri)ocular tissues. The final diagnosis was a subspectacular abscess. Follow-up revealed that the SIS graft provided excellent healing and cosmesis of the surgical site. CONCLUSIONS: While there are reports of lymphatic fluid dissection between skin layers during ecdysis, which can result in an opaque spectacle, the fluid opacity in this case was attributed to a subspectacular abscess secondary to an ascending oral infection. Addition of biological wound dressing may contribute to positive post-enucleation outcome in the snake.

Prospective observational study of dogs with splenic mass rupture suggests potentially lower risk of malignancy and more favourable perioperative outcomes.

Haemoperitoneum secondary to ruptured splenic tumours can be either benign or malignant in origin. The majority of previous studies of canine haemoperitoneum have been retrospective, which are associated with well-recognized biases, such as the potential to underappreciate the diversity of outcomes in a complex presentation such as haemoperitoneum. This study seeks to prospectively define perioperative morbidity and mortality of haemoperitoneum in dogs secondary to ruptured splenic masses. Forty dogs with haemoperitoneum secondary to a ruptured splenic mass met the inclusion criteria. As expected, the cohort predominately consisted of older large breed dogs. All dogs underwent preoperative staging and had a splenectomy performed. Histopathologic analysis was performed on the splenic mass, as well as any possible metastatic lesions that were noted intra-operatively. Perioperative care outside of splenectomy was delivered in specialty practices using current conventional approaches to care (eg, transfusions and anti-arrhythmic medications). Fifteen dogs (37.5%) had benign splenic tumours and were cured with surgery alone, whereas 62.5% had malignant disease (most often haemangiosarcoma [HSA]). Surgical outcomes were highly favourable in the vast majority of dogs. Indeed, 38 dogs (95%) survived and were discharged after a median hospitalization of 39.5 hours. Independent predictors of longer hospitalization times included receiving a transfusion and the development of an arrhythmia. Although small, this cohort defines distinctive and optimistic perspectives for dogs with haemoperitoneum from splenic tumour rupture. These favourable outcomes from this prospective study are sufficient to ask if larger prospective studies should be conducted to better inform owners during this challenging cancer emergency presentation.

Phosphorylated KIT as a predictor of outcome in canine mast cell tumours treated with toceranib phosphate or vinblastine.

Canine cutaneous mast cell tumour (MCT) is the most common malignant skin tumour in dogs and can exhibit variable biologic behaviour. Dysregulated signalling through the receptor tyrosine kinase (RTK) KIT can promote cell proliferation and survival, and assessment of its dysregulation via detection of activating c-kit gene mutations or assessment of KIT protein localization is associated with multiple features of malignancy. The aim of the current study was to use a previously validated immunohistochemical (IHC) assay to directly measure phosphorylated KIT (pKIT) in order to investigate its association with other established prognostic markers, response to therapy, progression free interval (PFI) and overall survival time (OST) in dogs treated medically for measurable MCT. Tumour tissue from 74 dogs enrolled in a prospective study comparing toceranib and vinblastine for MCT treatment were evaluated for pKIT immunoreactivity. pKIT was variably expressed, with some degree of positivity observed in 49/74 cases (66%). pKIT immunoreactivity was significantly associated with aberrant KIT localization, high mitotic index and high histologic grade. On univariate analysis, pKIT immunoreactivity predicted shorter PFI and OST in the entire patient population as well as shorter PFI in the toceranib treated group, and was the sole predictive factor for OST upon multivariate analysis, while mitotic index was the sole independent predictive factor for PFI. These results demonstrate that IHC detection of pKIT correlates with several features of aggressive behaviour, and may confer information that is complementary to other prognostic factors. However, the role of pKIT in predicting outcome needs to be studied further before recommendations can be made for its routine use.

Prospective evaluation of flow cytometric characteristics, histopathologic diagnosis and clinical outcome in dogs with naïve B-cell lymphoma treated with a 19-week CHOP protocol.

Canine B-cell lymphoma is a clinically heterogenous disease; however, it is generally treated as a single disease entity. The purpose of this clinical trial was to prospectively evaluate naïve canine B-cell lymphoma patients using histopathology, flow cytometry (FC) and a standardized chemotherapy protocol to better define subsets of this disease that may respond differently to treatment. Sixty-four dogs with naïve multicentric B-cell lymphoma were treated with a standardized 19-week CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) chemotherapy protocol. Most of the dogs (84.3%) were diagnosed with diffuse large B-cell lymphoma (DLBCL), followed by nodal marginal zone (7.8%), small B-cell (4.7%), Burkitt-like (1.6%) and follicular lymphoma (1.6%). FC confirmed the diagnosis of B-cell lymphoma in all cases. There were no clear phenotyping differences between the subtypes of B-cell lymphoma detectable by our FC panel. The histologic subtypes in this study exhibited a range of forward scatter values on flow cytometry, but all of the DLBCL cases were higher than a value of 469, while the only cases with a lower forward scatter value were follicular lymphoma and diffuse small B-cell lymphoma. Dogs with DLBCL had a significantly better objective response rate to the CHOP protocol (96.3%) than the non-DLBCL subtypes (70%, P = .024). The median progression-free survival time for patients with DLBCL (233 days) was significantly longer than that of all other histopathologic subgroups combined (163 days, P = .0005).

Polymerase chain reaction for antigen receptor rearrangement: Benchmarking performance of a lymphoid clonality assay in diverse canine sample types.

BACKGROUND: Polymerase chain reaction for antigen receptor rearrangement (PARR) is a molecular diagnostic tool used for discrimination of lymphoid malignancies in dogs from benign processes. Assay variations have been described and are commercially available, but performance metrics are not uniformly reported. OBJECTIVES: To describe performance (accuracy, sensitivity, specificity) and rigorous benchmarking of a PARR protocol (ePARR) in clinically relevant samples. ANIMALS: One hundred eighty-one client-owned dogs. METHODS: Lymphoma and benign tissues representative of the clinical spectrum with gold standard histopathologic and immunohistochemical diagnoses were collected. Assay development and benchmarking were performed on fresh frozen (FF) tissue, formalin-fixed paraffin-embedded (FFPE) tissue, flow cytometry pellets, and air-dried fine-needle aspirates (FNA). Assay performance was determined for FFPE from 56 dogs (18 B-cell lymphoma, 24 T-cell lymphoma, and 14 non-lymphoma), 80 frozen flow cytometry pellets (66 B-cell lymphoma, 14 T-cell lymphoma, 0 non-lymphoma), and 41 air-dried FNA slides (23 lymphoma, 18 non-lymphoma). RESULTS: For discrimination of lymphoma versus non-lymphoma, ePARR had 92% and 92% sensitivity and specificity on FFPE with 92% accuracy, 85% sensitivity from flow cytometry pellets (non-lymphoma was not evaluated to calculate specificity) with 85% accuracy, and 100% and 100% sensitivity and specificity for FNA with 100% accuracy. Stringent quality control criteria decreased assay success rate without significant performance improvement. Performance metrics were lower in most cases for discrimination of B- or T-cell versus non-B- or non-T-cell samples than for lymphoma versus non-lymphoma. CONCLUSIONS AND CLINICAL IMPORTANCE: These benchmarking data facilitate effective interpretation and application of PARR assays in multiple sample types.

Canine CD4+ T-cell lymphoma identified by flow cytometry exhibits a consistent histomorphology and gene expression profile.

T-cell lymphomas (TCL) are a diverse group of neoplasms with variable diagnostic features, pathophysiologies, therapeutic responses and clinical outcomes. In dogs, TCL includes indolent and aggressive tumours such as T-zone lymphoma (TZL) and peripheral T-cell lymphoma (PTCL), respectively. Delineation of molecular subtypes and investigation into underlying pathophysiologies of aggressive TCLs remains inadequate. We investigate the correlations between flow cytometry and histopathology of 73 cases of nodal TCL. The majority of cases (82.2%) were characterized as CD4+ TCL by flow cytometry. Fewer cases were classified as CD8+ TCL (6.8%) or CD4- CD8- TCL (11.0%). All cases, regardless of immunophenotype, exhibited conserved histologic features consistent with the WHO classification of PTCL. Histologic subsets of PTCL corresponding to immunophenotypic features were not identified. Neoplastic cell size determined by flow cytometry correlated significantly with mitotic rate. RNA-seq was performed on a subset of CD4+ PTCL cases (n = 6) and compared with sorted control CD4+ T-cells. The gene expression pattern of CD4+ PTCL was similar between all cases regardless of breed. PTCL was enriched in pathways representing G-coupled protein receptor signalling, extracellular matrix remodelling and vascular development, immune signalling and mitotic activity. Furthermore, global gene expression changes were consistent with downregulation of PTEN signalling and upregulation of the MTOR-PI3K-ATK axis. In this study, we evaluated the correlations between flow cytometry, histopathology and gene expression within a large cohort of nodal TCLs. We further demonstrate the ability of flow cytometry to identify a subtype of T-cell lymphoma, CD4+ PTCL, with a uniform histomorphology and gene expression profile.

Lateral manus translation for limb-sparing surgery in 18 dogs with distal radial osteosarcoma in dogs.

OBJECTIVE: To describe and report outcomes after lateral translation of the manus for limb-sparing management of distal radial osteosarcoma in dogs. STUDY DESIGN: Retrospective case series. STUDY POPULATION: Eighteen client-owned dogs. METHODS: The distal aspect of the affected radius and associated neoplastic tissues were excised. The distal aspect of the ulna was preserved except for its medial cortex, which was removed en bloc with the radial segment. The manus was translated laterally to place the radial carpal bone in contact with the distal aspect of the ulna. A limb-sparing or locking compression plate was placed on the remaining proximal radius and the 3rd metacarpal bone. A 3.5-mm SOP (string of pearls) plate was placed on the lateral aspect of the proximal ulna and the 4th metacarpal bone. Dogs were administered chemotherapy. Data were collected to assess surgical and oncologic outcomes. Limb function was subjectively assessed. RESULTS: The percentage of radius removed ranged from 43% to 94% (median 54%). Complications developed in 12 limbs, with infection in 10, biomechanical complications in 6, and local recurrence in 4. Limb function was subjectively assessed as acceptable. Median disease-free interval was 219 days, and median survival time was 370 days. CONCLUSION: Outcomes after lateral translation of the manus compared favorably to other limb-sparing techniques for dogs with distal radial osteosarcoma, particularly in dogs requiring excision of a large segment of the radius. CLINICAL SIGNIFICANCE: The lateral manus translation provides an alternative limb-sparing technique that does not require an allograft, endoprosthesis, or autograft.

NCI Comparative Oncology Program Testing of Non-Camptothecin Indenoisoquinoline Topoisomerase I Inhibitors in Naturally Occurring Canine Lymphoma.

PURPOSE: Only one chemical class of topoisomerase I (TOP1) inhibitors is FDA approved, the camptothecins with irinotecan and topotecan widely used. Because of their limitations (chemical instability, drug efflux-mediated resistance, and diarrhea), novel TOP1 inhibitors are warranted. Indenoisoquinoline non-camptothecin topoisomerase I (TOP1) inhibitors overcome chemical instability and drug resistance that limit camptothecin use. Three indenoisoquinolines, LMP400 (indotecan), LMP776 (indimitecan), and LMP744, were examined in a phase I study for lymphoma-bearing dogs to evaluate differential efficacy, pharmacodynamics, toxicology, and pharmacokinetics. EXPERIMENTAL DESIGN: Eighty-four client-owned dogs with lymphomas were enrolled in dose-escalation cohorts for each indenoisoquinoline, with an expansion phase for LMP744. Efficacy, tolerability, pharmacokinetics, and target engagement were determined. RESULTS: The MTDs were 17.5 mg/m2 for LMP 776 and 100 mg/m2 for LMP744; bone marrow toxicity was dose-limiting; up to 65 mg/m2 LMP400 was well-tolerated and MTD was not reached. None of the drugs induced notable diarrhea. Sustained tumor accumulation was observed for LMP744; γH2AX induction was demonstrated in tumors 2 and 6 hours after treatment; a decrease in TOP1 protein was observed in most lymphoma samples across all compounds and dose levels, which is consistent with the fact that tumor response was also observed at low doses LMP744. Objective responses were documented for all indenoisoquinolines; efficacy (13/19 dogs) was greatest for LMP744. CONCLUSIONS: These results demonstrate proof-of-mechanism for indenoisoquinoline TOP1 inhibitors supporting their further clinical development. They also highlight the value of the NCI Comparative Oncology Program (https://ccr.cancer.gov/Comparative-Oncology-Program) for evaluating novel therapies in immunocompetent pets with cancers.

Pilot study utilizing Fluorine-18 fluorodeoxyglucose-positron emission tomography/computed tomography for glycolytic phenotyping of canine mast cell tumors.

The goal of this prospective pilot study was to use naturally occurring canine mast cell tumors of various grades and stages as a model for attempting to determine how glucose uptake and markers of biologic behavior are correlated. It was hypothesized that enhanced glucose uptake, as measured by 2-[fluorine-18]fluoro-d-glucose-positron emission tomography/computed tomography (F18 FDG PET-CT), would correlate with histologic grade. Dogs were recruited for this study from a population referred for treatment of cytologically or histologically confirmed mast cell tumors. Patients were staged utilizing standard of care methods (abdominal ultrasound and three view thoracic radiographs), followed by a whole body F18 FDG PET-CT. Results of the F18 FDG PET-CT were analyzed for possible metastasis and standard uptake value maximum (SUVmax ) of identified lesions. Incisional or excisional biopsies of the accessible mast cell tumors were obtained and histology performed. Results were then analyzed to look for a possible correlation between the grade of mast cell tumors and SUVmax . A total of nine animals were included in the sample. Findings indicated that there was a correlation between grade of mast cell tumors and SUVmax as determined by F18 FDG PET-CT (p-value = 0.073, significance ≤ 0.1). Based on the limited power of this study, it is felt that further research to examine the relationship between glucose utilization and biologic aggressiveness in canine mast cell tumors is warranted. This study was unable to show that F18 FDG PET-CT was a better staging tool than standard of care methods.

Clinicopathologic features of lingual canine T-zone lymphoma.

Canine T-zone lymphoma (TZL) is a subtype of T-cell lymphoma characterized by unique histologic pattern and cytomorphology, immunophenotypic loss of CD45 expression, and an indolent clinical behaviour. Dogs with TZL typically present with 1 or more enlarged lymph nodes and/or lymphocytosis. We describe a novel extranodal presentation of TZL involving the tongue. Twelve dogs with tongue masses were diagnosed with lingual TZL based on a variable combination of immunophenotyping via flow cytometry, cytology, histopathology, immunohistochemistry and/or PCR for antigen receptor rearrangement (PARR) assay. Eleven dogs exhibited concurrent lymphocytosis and/or lymph node enlargement. Three cases were initially diagnosed as plasma cell tumours based on histology alone, thereby revealing a potential diagnostic challenge. Seven dogs achieved clinical remission and 4 achieved stable disease following variable treatment, consistent with the indolent nature of typical TZL involving the lymph nodes and peripheral blood. In 1 case the TZL resulted in progressive disease and failure to respond to treatment. In this case, the TZL exhibited histologic features of a higher grade neoplasm. This case series highlights a unique presentation of TZL and identifies a new differential diagnosis for lingual neoplasia. In this study, we characterize the clinical presentation, diagnostic features and patient outcomes of 12 dogs with lingual TZL.

c-Kit Mutation and Localization Status as Response Predictors in Mast Cell Tumors in Dogs Treated with Prednisone and Toceranib or Vinblastine.

BACKGROUND: KIT inhibitors, such as toceranib (TOC), and vinblastine (VBL) have not been prospectively compared in the treatment of macroscopic mast cell tumors (MCTs). Also, it is unknown whether VBL or TOC is superior for treating MCT without c-kit mutations. HYPOTHESIS/OBJECTIVES: To determine the value of KIT genotyping and localization in treatment decisions for dogs with macroscopic MCT. We hypothesized that c-kit mutated MCT would have a better response to TOC than VBL. ANIMALS: Eighty-eight client-owned dogs with macroscopic MCT. METHODS: Prospective, randomized trial. Dogs were randomized to TOC (2.75 mg/kg EOD) or VBL (2.5 mg/m2 weekly × 4 then EOW) by KIT localization and c-kit mutation status using an adaptive randomization scheme. RESULTS: Sixty dogs were allocated to TOC and 28 to VBL. Of the dogs receiving TOC, 20% had c-kit mutations, compared to 30% receiving VBL (P = 0.74). Overall response rates were 46% (TOC) and 30% (VBL) (odds ratio = 1.56 [0.62-3.92]; P = 0.28). Median progression-free survival (PFS) for dogs receiving VBL was 78 days (7-1,521) and for TOC 95.5 (14-990); hazard ratio (HR) = 1.34 [0.72-2.50]; P = 0.36. Median overall survival (OS) was 241.5 days (10-1,521) for the VBL group and 159 (20-990) for the TOC group; HR = 0.80 ([0.45-1.41]; P = 0.44). CONCLUSIONS AND CLINICAL IMPORTANCE: Neither PFS nor OS was significantly different between treatment groups. As the proportion of dogs with c-kit mutations was not different between treatment groups in this population of dogs, c-kit mutation status did not predict treatment response.

Expression of Phosphorylated KIT in Canine Mast Cell Tumor.

Canine cutaneous mast cell tumor (MCT) is the most common canine skin tumor and exhibits variable biologic behavior. Signaling through the KIT receptor tyrosine kinase promotes cellular proliferation and survival and has been shown to play a role in MCT progression. Despite investigations into numerous biomarkers and the proposal of several grading schemas, no single marker or grading system can accurately predict outcome in canine MCT. The first aim of this study was to develop an immunohistochemical assay to measure phosphorylated KIT (pKIT) to investigate its association with 2 commonly used grading systems and other established prognostic markers for canine MCT. Thirty-four archived MCTs were evaluated for expression of pKIT and Ki-67, KIT localization, mitotic count, mutations in exons 8 and 11 in c-kit, and grading by the Patnaik and 2-tier systems. Expression of pKIT was significantly ( P < .05) correlated with the 2-tier grading scheme and c-kit mutation. Correlation approached significance ( P = .06) with Mitotic Index (MI) and Ki-67. An additional aim was to determine whether pKIT labeling provides a pharmacodynamic marker for predicting response to the receptor tyrosine kinase inhibitor toceranib (TOC). MCTs from 4 of 7 patients demonstrated a partial response to TOC. pKIT expression was assessed by immunohistochemistry in biopsies obtained before and 6 hours after the patients were treated with TOC. Reduced pKIT expression after TOC treatment was demonstrated in 3 of the 4 patients with a partial response compared to 1 of the 3 nonresponders. Collectively, these results demonstrate that immunohistochemical detection of pKIT may be a clinically relevant assay to evaluate the activation status of the major oncogenic pathway in canine MCT.

Canine and feline retinal lymphoma: a retrospective review of 12 cases.

This retrospective study identified 12 cases (6 canine and 6 feline) of ocular lymphoma with extensive retinal involvement and relative sparing of other ocular tissues. Our objectives were to describe the morphologic and immunohistochemical features of retinal lymphoma, assess the degree of correlation to the human counterpart, assign subtypes based on the veterinary-adapted WHO classification system, and promote accurate reporting of retinal involvement in cases of intraocular lymphoma. Our findings suggest that a distinct retinal tropism is quite rare, representing approximately 1% of all cases of canine and feline ocular lymphoma. No breed or sex predispositions were identified. The mean age of the affected animal was 7 years (range 4-10) and 11 years (range 6-19) for dogs and cats, respectively. Nine cases (5 canine and 4 feline) were classified as diffuse large B-cell lymphoma (DLBCL) subtype. The remaining cases were classified as peripheral T-cell lymphoma (PTCL).