Fracture in drug-eluting stents increases focal intimal hyperplasia in the atherosclerosed rabbit iliac artery.

OBJECTIVES: Drug-eluting stent (DES) strut fracture (SF) is associated with higher incidence of In-stent restenosis (ISR)-return of blockage in a diseased artery post stenting-than seen with bare metal stents (BMS). We hypothesize that concomitance of drug and SF leads to greater neointimal response. BACKGROUND: Controlled release of therapeutic agents, such as sirolimus and its analogs, or paclitaxel from has reduced tissue based DES failure modes compared to BMS. ISR is dramatically reduced and yet the implications of mechanical device failure is magnified. METHODS: Bilateral Xience Everolimus-eluting stents (EES) were implanted in 20 New Zealand White rabbits on normal (n = 7) or high fat (HF)/high cholesterol (HC) (n = 13) diets. Implanted stents were intact or mechanically fractured. Everolimus concentration was as packaged or pre-eluted. After 21 days, stented vessels were explanted, resin embedded, MicroCT scanned, and analyzed histomorphometrically. RESULTS: Fractured EES were associated with significant (P < 0.05) increases in arterial stenosis and neointimal formation and lower lumen-to-artery area ratios compared to intact EES. Hyperlipidemic animals receiving pre-eluted EES revealed no significant difference between intact and fracture groups. CONCLUSIONS: SF increases intimal hyperplasia, post EES implant, and worse with more advanced disease. Pre-eluted groups, reflective of BMS, did not show significant differences, suggesting a synergistic effect of everolimus and mechanical injury, potentially explaining the lack of SF reports for BMS. Here, we report that ISR has a higher incidence with SF in EES, the clinical implication is that patients with SF after DES implantation merit careful follow-up.

Preclinical Evaluation of Mesh Implants: The Pathologist's Perspective.

Surgical and laparoscopic implantation of mesh devices is on the rise for a variety of applications. The complexity and range of evolving mesh designs calls for consistent and detailed pathologic evaluation in determining host responses and assessing overall safety. This review addresses the components of evaluation of mesh implants in animal models, with emphasis on histologic parameters, semiquantitative scoring matrices, and morphometric analyses that have been specifically adapted to this class of implants. Necropsy assessment should include implant persistence, architecture, and associated host responses such as exudation and adhesions. Microscopic evaluation should focus on primary relevant responses such as bioresorption, integration/tissue ingrowth, neovascularization, and inflammation. Selection of the best means of processing and evaluation can be complicated, as meshes may include one or more biologic components (e.g., collagen), synthetic polymer fibers, coatings, and other molecules. The architecture of some meshes can influence tissue responses and complicate sampling, sectioning, and evaluation. Recognition of specific study objectives and knowledge of anticipated responses helps to determine the appropriate histologic or immunochemical stains, while understanding of mesh composition and anticipated persistence in tissue determines the suitability of paraffin or resin embedding, and both guide the evaluation of mesh devices in the preclinical setting.

An Overview on the Considerations for the Planning of Nonclinical Necropsies for Medical Device Studies.

The terminal collection and histological processing of medical devices is an expensive, labor-, and material-intensive endeavor, which requires adequate experience, innovation, and preparation for success. It is also an exciting endeavor that continually challenges, intellectually engages, and improves the skills and knowledge of the pathologist. Awareness of the importance of the medical device pathologist's involvement, communication, and oversight throughout the development, implementation, and execution of a nonclinical assessment of a medical device is in the best interest of the test facility, the histopathology laboratory, the pathologist, the sponsor, and, ultimately, the patients. This article serves to present as a primer of key considerations for the approach and conduct of "nontoxicological" studies, defined as studies involving animal models of deployment or implantation of medical devices as well as surgical animal models.

Pharmacokinetics and safety of paclitaxel delivery into porcine airway walls by a new endobronchial drug delivery catheter.

BACKGROUND AND OBJECTIVE: Intratumoral administration of chemotherapeutic agents is a treatment modality that has proven efficacious in reducing the recurrence of tumours and increases specificity of treatment while minimizing systemic side effects. Direct intratumoral injection of malignant airway obstruction has potential therapeutic benefits but tissue drug concentrations and side-effect profiles are poorly understood. METHODS: Bronchial wall injection of generic paclitaxel (PTX) (102 injections of 0.05, 0.5, 1.5 or 2.5 mg/mL in 10 healthy pigs), saline (14 injections in 2 healthy pigs) or Abraxane (ABX) (24 injections of 0.5 mg/mL in 4 healthy pigs) was performed with a microneedle infusion catheter. Local histopathology, plasma and tissue PTX concentrations were evaluated at 7, 20 or 28 days post-injection. RESULTS: Injection of generic PTX directly into the bronchial wall at doses up to 1.5 mg/mL only caused minimal tissue injury. Dose-limiting tissue reaction was observed at 2.5 mg/mL. Plasma PTX was detectable for up to 5 days but not at 28 days, with area under the curve (AUC)(0-5d) 20- to 50-fold lower than the AUC(0-∞) of 6300 ng h/mL for the approved intravenous dose. At 7 and 28 days post-injection, bronchial PTX tissue concentrations were above a 10-nmol/L cancer therapeutic level. PTX was not found in peripheral tissues. Similar results were observed between ABX and generic PTX. CONCLUSION: Results of these studies confirm the administration of PTX directly into the bronchial wall is safe and feasible. PTX was detectable in plasma for <7 days but tissue concentrations remained therapeutic throughout the follow-up period.

Percutaneous Hepatic Perfusion With Filtered Melphalan for Localized Treatment of Metastatic Hepatic Disease: A Risk Assessment.

Regional therapies for metastatic liver disease have garnered interest in recent years due to technological advances in drug delivery. A percutaneous hepatic perfusion (PHP) using a newly developed generation 2 (GEN2) filtration system was designed to mitigate systemic toxicity and cardiovascular risk associated with hepatic blood filtration during hepatic artery infusion of the chemotherapy drug melphalan. The GEN2 system was evaluated in healthy swine, and plasma samples were assessed for clinical chemistry, melphalan toxicokinetics (TK), inflammatory cytokines, catecholamines, hematological, and cardiac biomarkers. Cardiovascular safety was assessed by echocardiography, electrocardiogram, and telemetry. Toxicology parameters included clinical signs, body weight, gross pathology, and histopathology. There were no treatment-related deaths associated with the PHP procedure with GEN2 filtration, and all animals survived to scheduled necropsy. Assessment of the pharmacokinetic/TK plasma concentrations of melphalan demonstrated that the GEN2 filter was able to extract melphalan from blood with high efficiency and reduce melphalan exposure in the systemic circulation. The hemodynamic, immunosuppressive, immunotoxic, cardiotoxic, and histopathologic effects of melphalan were limited. The significant hemodynamic challenge imposed by filtration resulted in a compensatory tachycardia with supranormal left ventricular function, although no wall motion abnormalities were detected and left ventricular function remained normal. Catecholamines decreased and then quickly rebounded during washout. Transient and reversible effects of treatment on cardiac enzymes, catecholamines, and cytokines and reversible hemodynamic effects without cardiac damage indicated that PHP with melphalan was not cardiotoxic or immunotoxic under the conditions tested, due to high efficiency of the filtration system limiting exposure of melphalan to the systemic circulation.

Procedural and Anatomical Determinants of Multielectrode Renal Denervation Efficacy.

Radiofrequency renal denervation is under investigation for treatment of hypertension with variable success. We developed preclinical models to examine the dependence of ablation biomarkers on renal denervation treatment parameters and anatomic variables. One hundred twenty-nine porcine renal arteries were denervated with an irrigated radiofrequency catheter with multiple helically arrayed electrodes. Nerve effects and ablation geometries at 7 days were characterized histomorphometrically and correlated with associated renal norepinephrine levels. Norepinephrine exhibited a threshold dependence on the percentage of affected nerves across the range of treatment durations (30-60 s) and power set points (6-20 W). For 15 W/30 s treatments, norepinephrine reduction and percentage of affected nerves tracked with number of electrode treatments, confirming additive effects of helically staggered ablations. Threshold effects were only attained when ≥4 electrodes were powered. Histomorphometry and computational modeling both illustrated that radiofrequency treatments directed at large neighboring veins resulted in subaverage ablation areas and, therefore, contributed suboptimally to efficacy. Account for measured nerve distribution patterns and the annular geometry of the artery revealed that, regardless of treatment variables, total ablation area and circumferential coverage were the prime determinants of renal denervation efficacy, with increased efficacy at smaller diameters.

What is your diagnosis? Cervical mass in a cat.

An 8-year-old female spayed domestic shorthair cat was presented for several months of weight loss, decreased appetite, and 2 bilateral, ventral cervical masses. Initial cytologic samples were interpreted as reactive lymphoid hyperplasia. Evaluation of subsequent mass aspirates revealed small numbers of large binucleated and multinucleated cells resembling Reed-Sternberg cells admixed with more numerous small and intermediate-sized lymphocytes. In histopathologic sections, the normal architecture of the lymph node was largely effaced by a slightly heterogeneous mass composed of round cells arranged in densely cellular sheets with a minor population of large (25-microm diameter) mononuclear cells and a few very large (30-40-microm diameter) binucleated or multinucleated cells interpreted as Reed-Sternberg-like cells. Immunohistochemically, the large neoplastic (Reed-Sternberg-like) cells were negative for CD18, CD3, CD20, and CD79a while the background population consisted of about 70% T cells and 30% B cells. This pattern of immunohistochemical staining along with cytologic and histopathologic findings supported a diagnosis of Hodgkin's-like lymphoma, specifically, the lymphocyte-rich subtype. Hodgkin's-like lymphoma has been reported previously in cats and should be suspected when Reed-Sternberg-like cells are observed in cytologic preparations of lymph node aspirates. Histopathology and immunohistochemistry are necessary for a definitive diagnosis.

Retrospective analysis of corrosion and ion release from retrieved cast stainless steel tibia plateau leveling osteotomy plates in dogs with and without peri-implant osteosarcoma.

OBJECTIVE To evaluate and compare surface and cross-sectional structure as well as localized electrochemical corrosion and ion release for cast stainless steel (SS) tibia plateau leveling osteotomy (TPLO) plates retrieved from dogs with and without osteosarcoma (OSA) and to compare these findings with similar variables for forged SS TPLO plates retrieved from dogs. SAMPLE 47 TPLO plates explanted from 45 client-owned dogs (22 cast plates from dogs with OSA, 22 cast plates from dogs without OSA, and 3 forged plates from dogs without OSA). PROCEDURES Histologic evaluations of tissue samples collected from implant sites at the time of plate retrieval were performed to confirm implant site tumor status of each dog. Surfaces and metallographic cross sections of retrieved plates were examined, and the microcell technique was used to obtain local electrochemical corrosion and ion release measurements. RESULTS Findings indicated that all cast SS plates demonstrated high spatial variability of their electrochemical surface properties and inhomogeneous superficial and cross-sectional composition, compared with forged plates. Greater metal ion release was observed in cast plates than in forged plates and in cast plates from dogs with OSA than in cast or forged from dogs without OSA. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that accumulation of metal ions from implants could be a trigger for neoplastic transformation in neighboring cells. Metal ion release caused by corrosion of implants that do not comply with recommended standards of the American Society for Testing and Materials International or the International Organization for Standardization could potentially place patients at increased risk of tumor development.

Chronic hepatitis in Labrador Retrievers: clinical presentation and prognostic factors.

BACKGROUND: An increased incidence of chronic hepatitis has been reported in Labrador Retrievers. HYPOTHESIS: A breed associated hepatopathy occurs in Labrador Retrievers. ANIMALS: Twenty-four client-owned Labrador Retrievers. METHODS: Medical records of dogs with histopathologic confirmation of chronic hepatitis were retrospectively reviewed. A clinical score based on clinical signs and the results of biochemical tests was generated for each dog. Hepatic biopsy specimens were scored for disease activity, fibrosis, and copper accumulation. RESULTS: The median age was 9.3 years (range, 3.9-14.0 years). Clinical signs included inappetence, vomiting, lethargy, and weight loss. All dogs had increases in serum activity of one or more hepatobiliary enzyme. Hyperbilirubinemia and hypoalbuminemia were present in 45% and 21% of dogs, respectively. The median clinical score was 2.9, with a range of 0-8. The median histopathology activity and the fibrosis scores were 3.5 (range, 1-6) and 3.0 (range, 0-4), respectively. Rhodanine-positive copper staining was present in 15 of 17 biopsy specimens, with a median score of 2.0 (range, 0-3). Median survival was 374 days (range, 1-2645 days). A prolonged prothrombin time (P = .013) and thrombocytopenia (P = .041) were associated with survival < 2 months. The presence of anorexia (P = .049), hypoglobulinemia (P = .045), or prolonged partial thromboplastin time (P = .033) were associated with shorter overall survival times. The clinical score correlated with survival time (P = .030) and histopathologic staging (P = .049). CONCLUSIONS AND CLINICAL IMPORTANCE: A progressive hepatopathy in Labrador Retrievers in this study was marked by chronic inflammation, fibrosis, and copper accumulation. A clinical scoring system that correlates with survival time may be useful as a noninvasive method to predict prognosis.

Clinical characterization of a familial degenerative myelopathy in Pembroke Welsh Corgi dogs.

BACKGROUND: Adult dogs with degenerative myelopathy (DM) have progressive ataxia and paresis of the pelvic limbs, leading to paraplegia and euthanasia. Although most commonly reported in German Shepherd dogs, high disease prevalence exists in other breeds. OBJECTIVE: Our aim was the clinical and histopathologic characterization of familial degenerative myelopathy (FDM) in Pembroke Welsh Corgi (PWC) dogs. ANIMALS: Twenty-one PWCs were prospectively studied from initial diagnosis until euthanasia. METHODS: Neurologic examination, blood tests, cerebrospinal fluid (CSF) analysis, electrodiagnostic testing, and spinal imaging were performed. Concentrations of 8-iso-prostaglandin F2alpha (8-isoprostane) were measured in CSF. Routine histochemistry was used for neuropathology. Deoxyribonucleic acid and pedigrees were collected from 110 dogs. RESULTS: Median duration of clinical signs before euthanasia was 19 months. Median age at euthanasia was 13 years. All dogs were nonambulatory paraparetic or paraplegic, and 15 dogs had thoracic limb weakness at euthanasia. Electrodiagnostic testing and spinal imaging were consistent with noncompressive myelopathy. No significant difference was detected in 8-isoprostane concentrations between normal and FDM-affected dogs. Axonal and myelin degeneration of the spinal cord was most severe in the dorsal portion of the lateral funiculus. Pedigree analysis suggested a familial disease. CONCLUSIONS AND CLINICAL IMPORTANCE: Clinical progression of FDM in PWC dogs was similar to that observed in other breeds but characterized by a longer duration. Spinal cord pathology predominates as noninflammatory axonal degeneration. Oxidative stress injury associated with 8-isoprostane production is not involved in the pathogenesis of FDM-affected PWC dogs. A familial disease is suspected.

Immediate mandibular reconstruction of a 5 cm defect using rhBMP-2 after partial mandibulectomy in a dog.

OBJECTIVE: To report treatment of a complex odontoma of the mandible by partial mandibulectomy and immediate surgical reconstruction using bridging plate fixation with a synthetic graft. STUDY DESIGN: Clinical case report. ANIMALS: A 4-year-old male castrated cocker spaniel. METHODS: Immediate reconstruction of the left mandible (5 cm gap) was performed after complete excision of a complex odontoma. Locking plate fixation was applied immediately before complete excision of the mass. Fixation was removed, then after partial mandibulectomy, including all abnormal tissue, restored to achieve occlusion. The resulting mandibular defect was filled with recombinant human bone morphogenetic protein-2 (rhBMP-2) delivered in an absorbable collagen sponge containing hydroxyapatite/tricalcium phosphate granules (compression resistant matrix [CRM]). RESULTS: New bone growth was evident radiographically and on palpation at 3 months. Bony remodeling was evident during follow-up examinations up to 26 months. Bone collected by biopsy at the graft site at 7 months had robust new bone formation and evidence of continued remodeling. Only minor complications (repeated intraoral plate exposure) were encountered postoperatively and were easily resolved. CONCLUSIONS: An osteoinductive factor (rhBMP-2/CRM) was successfully used as a graft substitute in immediate reconstruction of a large mandibular defect. CLINICAL RELEVANCE: Immediate reconstruction of large mandibular defects with osteoinductive materials as a graft substitute may be a viable alternative to partial mandibular resection or radiation therapy for benign odontogenic tumors in dogs.

Multiple meningiomas in three dogs.

Three dogs with seizures were diagnosed with multiple intracranial meningiomas. Two of the three dogs were golden retrievers, and ages ranged from 9 to 11 years. Treatment consisted of surgery and radiation (n=2) or chemotherapy (n=1). In all three cases, the masses were two distinct tumors as determined by imaging, surgery, or necropsy. In two dogs, the meningiomas had the same histological pattern, while in one dog the histological subtypes were different.

No overt cellular inflammation around intravascular schistosomes in vivo.

Schistosomes are intravascular platyhelminth parasites that are exposed in the blood stream to host immunological effectors. Antibody-dependent cell-mediated cytotoxicity (ADCC) can act in vitro to kill the parasites, and this has been proposed as one important mechanism of antiworm immunity in vivo. In this study, we examined sections of adult Schistosoma mansoni in situ, within the vasculature of strains of mice that exhibit low (Balb/c) or high (CBA) pathology, and in the vasculature of infected chimpanzees, for evidence of cellular inflammation around the worms. In both mouse strains, we observe robust cellular inflammation around the parasite eggs in the intestines and liver tissue. However, we detect no overt cellular inflammation around the mature parasites in vivo. Likewise in the vasculature of infected chimpanzees, no immune cell accumulations are detected around adult schistosomes in situ. These data suggest that the parasites can promote a polar immune response that targets eggs (and assists the eggs to exit the host and continue the life cycle) but that does not effectively target the source of those eggs, namely, the adult worms.

Material properties of and tissue reaction to the Slocum TPLO plate.

OBJECTIVE: To determine the material properties of Slocum TPLO plates and assess the soft tissue reaction adjacent to these plates in dogs that had undergone tibial plateau leveling osteotomy (TPLO). SAMPLE POPULATION: 3 new TPLO plates, 8 retrieved TPLO plates, and 1 new Synthes dynamic compression plate. PROCEDURES: Metallurgic analyses were performed. Tissue samples were obtained from areas adjacent to retrieved plates and submitted for histologic examination. RESULTS: All of the TPLO plates had a 2-phase microstructure consisting of austenite and ferrite in various amounts. Residua, inclusions, and cavities were seen during microscopic examination of the plate surface. The major differences between new and retrieved TPLO plates were the presence of small gaps separating many inclusions from the surrounding matrix and the presence of various-sized pits on the surface of the retrieved plates. The dynamic compression plate had a nearly pure austenitic structure and was largely free from residua, inclusions, and cavities. Histologic examination of tissue samples obtained from areas adjacent to retrieved TPLO plates revealed intra- and extracellular particulate debris. Two types of particles (one consisting of chromium, nickel, molybdenum, and iron and the other consisting of aluminum and silicon) were seen. CONCLUSIONS AND CLINICAL RELEVANCE: Results determined that new and retrieved TPLO plates were manufactured from 316L stainless steel and produced by a casting process, but not all plates met specifications for chemical composition of cast surgical implants (American Society for Testing Materials standard F745); tissues surrounding retrieved plates had evidence of adverse reactions, probably as a result of plate corrosion.

Liver lobe torsion in dogs: 13 cases (1995-2004).

OBJECTIVE: To determine history, results of diagnostic testing, surgical findings, complications, and outcome for dogs with liver lobe torsion (LLT). DESIGN: Retrospective case series. ANIMALS: 12 dogs (1 with 2 episodes). PROCEDURE: Signalment, clinical signs, clinicopathologic findings, radiographic and ultrasonographic findings, surgical and histologic findings, complications, and hospitalization time were evaluated. RESULTS: The most common clinical signs were nonspecific abnormalities (eg, vomiting, lethargy, and anorexia) of acute or chronic duration. All dogs were large-breed dogs (median body weight, 37.2 kg [82 lb]). Biochemical abnormalities included high alanine amino-transferase (n = 12) and aspartate aminotransferase (11) activities. Results of abdominal ultrasonography were supportive of the diagnosis in 5 of 8 cases. Affected lobes included the left medial lobe (n = 4), left lateral lobe (3), papillary process of the caudate lobe (2), caudate lobe (1), and right lateral lobe (1). Exploratory celiotomy and liver lobectomy were performed in 12 of 13 cases, and in 11 of those 12 cases, the dog survived. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that development of nonspecific clinical signs of vomiting, lethargy, and anorexia in conjunction with high serum hepatic enzyme activities and mature neutrophilia in a medium-sized or large-breed dog should increase the index of suspicion for LLT. Abdominal ultrasonography with Doppler assessment may be useful in establishing the diagnosis. The long-term outcome for dogs that survive the hospitalization period is excellent.

Pathology of Endovascular Stents.

Contemporary endovascular stents are the product of an iterative design and development process that leverages evolving concepts in vascular biology and engineering. This article reviews how insights into vascular pathophysiology, materials science, and design mechanics drive stent design and explain modes of stent failure. Current knowledge of pathologic processes is providing a more complete picture of the factors mediating stent failure. Further evolution of endovascular stents includes bioresorbable platforms tailored to treat plaques acutely and to then disappear after lesion pacification. Ongoing refinement of stent technology will continue to require insights from pathology to understand adverse events, refine clinical protocols, and drive innovation.

Arterial microanatomy determines the success of energy-based renal denervation in controlling hypertension.

Renal denervation (RDN) is a treatment option for patients with hypertension resistant to conventional therapy. Clinical trials have demonstrated variable benefit. To understand the determinants of successful clinical response to this treatment, we integrated porcine and computational models of intravascular radiofrequency RDN. Controlled single-electrode denervation resulted in ablation zone geometries that varied in arc, area, and depth, depending on the composition of the adjacent tissue substructure. Computational simulations predicted that delivered power density was influenced by tissue substructure, and peaked at the conductivity discontinuities between soft fatty adventitia and water-rich tissues (media, lymph nodes, etc.), not at the electrode-tissue interface. Electrode irrigation protected arterial wall tissue adjacent to the electrode by clearing heat that diffuses from within the tissue, without altering periarterial ablation. Seven days after multielectrode treatments, renal norepinephrine and blood pressure were reduced. Blood pressure reductions were correlated with the size-weighted number of degenerative nerves, implying that the effectiveness of the treatment in decreasing hypertension depends on the extent of nerve injury and ablation, which in turn are determined by the tissue microanatomy at the electrode site. These results may explain the variable patient response to RDN and suggest a path to more robust outcomes.

Clinicopathological and ultrasonographic features of cats with eosinophilic enteritis.

Eosinophilic enteritis (EE) in cats is poorly characterized. The aim of the current study was to retrospectively evaluate the clinical and ultrasonographic findings in cats with histologic evidence of eosinophilic inflammation on gastrointestinal biopsy. Twenty-five cats with tissue eosinophilia on surgical (10) or endoscopic (15) biopsy of the gastrointestinal tract, having an abdominal ultrasound performed within 48 h of biopsy acquisition, were enrolled. History, clinical presentation, clinical pathology and abdominal ultrasound findings were reviewed. Intestinal biopsies were evaluated by a single pathologist and separated into two groups based on the degree of eosinophilic infiltrate: mild (<10 eosinophils/high-power field [HPF], 11/25 cats), or moderate/marked (>10 eosinophils/HPF, 14/25 cats). The former were considered primary lymphoplasmacytic or lymphocytic inflammatory bowel disease (LPE) with subtle eosinophilic infiltrates, and the latter to have EE. Signalment, history and clinical signs were similar in all cats. Only cats with EE (6/14) had palpably thickened intestines. The only distinguishing clinicopathological feature of cats with EE was the presence of peripheral eosinophilia (6/14). On ultrasound, when compared with cats with LPE, cats with EE had a greater mean jejunal wall thickness (3.34 mm ± 0.72 mm vs 4.07 mm ± 0.58 mm, respectively) and an increased incidence of thickening of the muscularis layer (1/11 and 11/14, respectively). In conclusion, ultrasonographic evidence of a prominent intestinal muscularis layer, palpably thickened intestines and peripheral eosinophilia can serve as biomarkers for the presence of EE in cats with chronic intestinal signs.

Cutaneous lymphoma of the tarsus in cats: 23 cases (2000-2012).

OBJECTIVE: To determine features of lymphoma of the tarsus in cats. DESIGN: Multi-institutional retrospective study. ANIMALS: 23 cats with cutaneous lymphoma of the tarsus. PROCEDURES: Veterinary oncologists were requested to submit cases fitting the following criteria: histologically or cytologically confirmed lymphoma with a location at or near the tarsus and described as subcutaneous or mass-like. Data regarding breed, sex, age, FeLV and FIV status, and reason for evaluation were collected. Results of staging tests, location of the tumor, immunophenotype, and histopathologic description were recorded. Type of treatments, outcome, survival time, presence or absence of progressive disease, and cause of death or reason for euthanasia were also recorded. RESULTS: Most cats were older, with a median age of 12 years (range, 7 to 18 years). No association with positive retroviral status was found. Popliteal lymph node involvement at diagnosis was reported in 5 cats, and a suspicion of lymphoma at a different site on the basis of results of abdominal ultrasonography was reported in 4 cats. Treatments were variable and included corticosteroids alone (n = 2), chemotherapy (9), radiation and chemotherapy (7), or surgery with or without chemotherapy (5). Thirteen cats were reported to have lymphoma at a different site at the time of last follow-up, death, or euthanasia. Median survival time for all cats in the study was 190 days (range, 17 to 1,011 days). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that tarsal lymphoma is an uncommon manifestation of lymphoma in cats, and in this study was most commonly nonepitheliotropic and of high grade as determined on histologic evaluation. Systemic involvement was identified; therefore, thorough staging is recommended prior to initiating treatment. Future studies are warranted to evaluate effective treatment protocols.