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The mitotic count (MC) is an important histological parameter for prognostication of malignant neoplasms. However, it has inter- and intraobserver discrepancies due to difficulties in selecting the region of interest (MC-ROI) and in identifying or classifying mitotic figures (MFs). Recent progress in the field of artificial intelligence has allowed the development of high-performance algorithms that may improve standardization of the MC. As algorithmic predictions are not flawless, computer-assisted review by pathologists may ensure reliability. In the present study, we compared partial (MC-ROI preselection) and full (additional visualization of MF candidates and display of algorithmic confidence values) computer-assisted MC analysis to the routine (unaided) MC analysis by 23 pathologists for whole-slide images of 50 canine cutaneous mast cell tumors (ccMCTs). Algorithmic predictions aimed to assist pathologists in detecting mitotic hotspot locations, reducing omission of MFs, and improving classification against imposters. The interobserver consistency for the MC significantly increased with computer assistance (interobserver correlation coefficient, ICC = 0.92) compared to the unaided approach (ICC = 0.70). Classification into prognostic stratifications had a higher accuracy with computer assistance. The algorithmically preselected hotspot MC-ROIs had a consistently higher MCs than the manually selected MC-ROIs. Compared to a ground truth (developed with immunohistochemistry for phosphohistone H3), pathologist performance in detecting individual MF was augmented when using computer assistance (F1-score of 0.68 increased to 0.79) with a reduction in false negatives by 38%. The results of this study demonstrate that computer assistance may lead to more reproducible and accurate MCs in ccMCTs.
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Aprendizaje Profundo , Algoritmos , Animales , Inteligencia Artificial , Perros , Humanos , Patólogos , Reproducibilidad de los ResultadosRESUMEN
A 30-year-old free-ranging female mountain gorilla (Gorilla beringei beringei) developed a perioral mass that was surgically debulked and diagnosed as malignant melanoma. After tumor recurrence, a canine melanoma vaccine was administered. However, the gorilla died shortly thereafter, and metastases to lymph nodes, lung, liver, and kidney were found post-mortem.
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Enfermedades de los Perros , Melanoma , Animales , Perros , Femenino , Gorilla gorilla , Melanoma/veterinariaRESUMEN
BACKGROUND: Neuroscience education therapy (NET) has been successfully used for numerous overlapping pain conditions, but few studies have investigated NET for migraine. OBJECTIVE: We sought to 1) review the literature on NET used for the treatment of various pain conditions to assess how NET has been studied thus far and 2) recommend considerations for future research of NET for the treatment of migraine. DESIGN/METHODS: Following the PRISMA guideline for scoping reviews, co-author (TR), a medical librarian, searched the MEDLINE, PsychInfo, Embase, and Cochrane Central Clinical Trials Registry databases for peer-reviewed articles describing NET to treat migraine and other chronic pain conditions. Each citation was reviewed by two trained independent reviewers. Conflicts were resolved through consensus. RESULTS: Overall, a NET curriculum consists of the following topics: pain does not equate to injury, pain is generated in the brain, perception, genetics, reward systems, fear, brain plasticity, and placebo/nocebo effects. Delivered through individual, group, or a combination of individual and group sessions, NET treatments often incorporate exercise programs and/or components of other evidence-based behavioral treatments. NET has significantly reduced catastrophizing, kinesiophobia, pain intensity, and disability in overlapping pain conditions. In migraine-specific studies, when implemented together with traditional pharmacological treatments, NET has emerged as a promising therapy by reducing migraine days, pain intensity and duration, and acute medication intake. CONCLUSION: NET is an established treatment for pain conditions, and future research should focus on refining NET for migraine, examining delivery modality, dosage, components of other behavioral therapies to integrate, and migraine-specific NET curricula.
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Dolor Crónico , Trastornos Migrañosos , Humanos , Trastornos Migrañosos/terapiaRESUMEN
BACKGROUND: Concurrent vasculopathic lesions in dogs with pemphigus foliaceus (PF) have been observed anecdotally yet not reported in the literature. Any association with prognosis is unclear. HYPOTHESIS/OBJECTIVES: To compare clinical features and outcome of PF in dogs with and without vasculopathic lesions. ANIMALS: Archived, formalin-fixed, paraffin-embedded biopsy samples of 41 dogs with PF. METHODS AND MATERIALS: Archived, formalin-fixed, paraffin-embedded biopsy samples with a histological diagnosis of PF were selected and re-evaluated independently. Dogs were assigned to groups following histological evaluation: Group 1 (no vasculopathic lesions) and Group 2 (vasculopathic lesions present). Group 2 was subdivided into Group 2a (vasculopathic lesions without vasculitis - i.e. vasculopathy) and Group 2b (overt vasculitis). Medical records from identified cases were reviewed retrospectively for data on clinical presentation, treatment and outcome. RESULTS: Time to remission was longer in Group 2b (93.8 days) compared to Group 1 (41.8 days) (P = 0.047). Dogs in groups 2a and 2b were more likely to have systemic signs of illness at presentation (P = 0.028 and P = 0.032, respectively) compared to Group 1. Dogs in Group 2b were more likely to have adverse effects associated with treatment than dogs in Group 1 (P = 0.004). There were no significant differences in lesion type, distribution, rates of remission, recurrence or corticosteroid dosage between groups. CONCLUSIONS AND CLINICAL IMPORTANCE: Dogs with PF and concurrent vasculitis took longer to achieve remission and were more likely to have systemic signs of illness or adverse effects associated with treatment than dogs with PF without concurrent vasculopathic lesions.
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Enfermedades de los Perros , Pénfigo , Animales , Enfermedades de los Perros/tratamiento farmacológico , Perros , Pénfigo/tratamiento farmacológico , Pénfigo/veterinaria , Pronóstico , Estudios Retrospectivos , Resultado del TratamientoRESUMEN
BACKGROUND: Headache mobile health (mHealth) applications (apps) have gained popularity in use but there is little research into what people with migraine find important to track. This information is important for helping with adherence and determining meaningful data to patients. We conducted several clinical trials using a headache research app (RELAXaHEAD). The app contains a "notes" feature (a free-text input section) where patients could record notes related to their headache. OBJECTIVE: To identify what patients view as important when tracking migraine/headaches within a headache tracking mHealth app. METHODS: This was a retrospective study where smartphone diary notes inputted by people with migraine were qualitatively analyzed; notes were extracted, a preliminary codebook was developed and used to code each note. Using grounded theory, themes and subthemes emerged. RESULTS: About 288 subjects in the trials used the notes function. There were 5364 total notes with an average of 18.6 ± 39.2 notes/user. The qualitative analysis yielded 759 unique codes and the emergence of 4 major themes. The first theme was "Utility in free-text tracking of headache characteristics, medications, and sleep" which emerged as a space for users to elaborate on data that could have been inputted into other sections of the app. The second theme was "Monitoring coexisting conditions both related to and distinct from headache." The third theme was "Personal records of behavioral therapy adherence," which included a range of concepts from behavioral therapy session frequency/adherence to subjects' thoughts or emotions regarding the behavioral therapy. The fourth theme was "Migraine trigger, prevention, and relief patterns deciphered through consistent data tracking." CONCLUSION: We found that the majority of patients choose to expand on information beyond what can be inputted into specific icons in a headache app. Moreover, they want to be able to monitor not only headache-related symptoms but symptoms they experience from other conditions. In addition to tracking their pharmacologic treatment, they may choose to track their nonpharmacologic, that is, behavioral therapy use, and they also use a smartphone diary app to assess what triggers versus relieves a migraine. While the RELAXaHEAD app was designed with features to extract data that would be useful to physicians and patients in treating migraine, our study results indicated that users also prefer a range of tracking capabilities that may or may not be useful to physicians but may be important for headache smartphone user engagement.
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Trastornos Migrañosos/terapia , Aplicaciones Móviles/estadística & datos numéricos , Participación del Paciente , Teléfono Inteligente/estadística & datos numéricos , Telemedicina/estadística & datos numéricos , Adulto , Actitud hacia los Computadores , Femenino , Humanos , Masculino , Persona de Mediana Edad , Investigación CualitativaRESUMEN
Mitotic count (MC) is an important element for grading canine cutaneous mast cell tumors (ccMCTs) and is determined in 10 consecutive high-power fields with the highest mitotic activity. However, there is variability in area selection between pathologists. In this study, the MC distribution and the effect of area selection on the MC were analyzed in ccMCTs. Two pathologists independently annotated all mitotic figures in whole-slide images of 28 ccMCTs (ground truth). Automated image analysis was used to examine the ground truth distribution of the MC throughout the tumor section area, which was compared with the manual MCs of 11 pathologists. Computerized analysis demonstrated high variability of the MC within different tumor areas. There were 6 MCTs with consistently low MCs (MC<7 in all tumor areas), 13 cases with mostly high MCs (MC ≥7 in ≥75% of 10 high-power field areas), and 9 borderline cases with variable MCs around 7, which is a cutoff value for ccMCT grading. There was inconsistency among pathologists in identifying the areas with the highest density of mitotic figures throughout the 3 ccMCT groups; only 51.9% of the counts were consistent with the highest 25% of the ground truth MC distribution. Regardless, there was substantial agreement between pathologists in detecting tumors with MC ≥7. Falsely low MCs below 7 mainly occurred in 4 of 9 borderline cases that had very few ground truth areas with MC ≥7. The findings of this study highlight the need to further standardize how to select the region of the tumor in which to determine the MC.
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Enfermedades de los Perros/patología , Técnicas Histológicas/veterinaria , Neoplasias Cutáneas/veterinaria , Animales , Recuento de Células/veterinaria , Perros , Procesamiento de Imagen Asistido por Computador , Mastocitos/patología , Índice Mitótico/veterinaria , Clasificación del Tumor/veterinaria , Variaciones Dependientes del Observador , Patólogos , Neoplasias Cutáneas/patología , Programas InformáticosRESUMEN
Rising rates of depression on university campuses accentuate the need for specific intervention. Interventions targeting disturbances in positive affect, in particular, remain sparse, yet such deficits interfere substantially with functioning and further exacerbate or maintain negative symptoms. The current study aimed to evaluate the impact of a virtual, two-session Behavioral Activation augmented with Savoring (BA + S) intervention compared to an Emotional Awareness (EA) control group in increasing positive affect. Sixty university students with low positive affect were randomized to BA + S or EA and completed 21 days of experience-sampling of positive affect. Weekly measures of positive and negative valence symptoms were assessed at baseline, sessions one and two, and at one-week follow-up. Through a prori analyses utilizing multilevel and multivariate multilevel models, our results demonstrate that daily positive affect measured via experience-sampling significantly improved in BA + S, whereas positive affect did not change for those receiving EA, though the interaction of condition and time was not significant. Furthermore, interactions in weekly variables were significant. Increases in positive valence symptoms (affect, anhedonia, etc.) were only reported for students receiving BA + S but not EA. Negative valence symptoms (affect, depression, general distress) improved in both conditions but with superior improvements in BA + S compared to EA. BA + S shows promise for a scalable and accessible intervention to university students with clinical levels of positive and negative affect. ClinicalTrials ID: NCT05234476.
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Estudiantes , Humanos , Estudiantes/psicología , Femenino , Masculino , Universidades , Adulto Joven , Adulto , Depresión/psicología , Depresión/terapia , Afecto , Terapia Conductista/métodos , AdolescenteRESUMEN
A 10-year-old spayed female Dachshund presented with abdominal pain and generalized severe ileus. An exploratory laparotomy was performed, confirming a severe ileus of undetermined origin. Multiple intestinal biopsy results confirmed acute intestinal leiomyositis. Immunohistochemistry (IHC) stains confirmed a T-cell predominant inflammatory infiltrate. Intravenous immunoglobulin (hIVIG) was administered prior to immunosuppressive therapy. Within 10 days of hIVIG treatment, functional peristaltic activity returned, and symptoms resolved. Long-term management, including the use of mycophenolate, resulted in sustained functional peristaltic recovery. Further studies are needed to explore the potential benefits of hIVIG treatment in the stabilization phase of this commonly fatal, treatment-refractory disease.
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Panic disorder is a common psychiatric diagnosis characterized by acute, distressing somatic symptoms that mimic medically-relevant symptoms. As a result, individuals with panic disorder overutilize personal and healthcare resources in an attempt to diagnose and treat physical symptoms that are often medically benign. A biobehavioral perspective on these symptoms is needed that integrates psychological and medical knowledge to avoid costly treatments and prolonged suffering. This narrative review examines six common somatic symptoms of panic attacks (non-cardiac chest pain, palpitations, dyspnea, dizziness, abdominal distress, and paresthesia), identified in the literature as the most severe, prevalent, or critical for differential diagnosis in somatic illness, including long COVID. We review somatic illnesses that are commonly comorbid or produce panic-like symptoms, their relevant risk factors, characteristics that assist in distinguishing them from panic, and treatment approaches that are typical for these conditions. Additionally, this review discusses key factors, including cultural considerations, to assist healthcare professionals in differentiating benign from medically relevant symptoms in panic sufferers.
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A 6-yr-old male red kangaroo (Macropus rufus) presented for a history of inappetance, abnormal behavior, and unconfirmed elimination for 6 hr prior to presentation. Based on abdominal ultrasound, abdominocentesis, and cystocentesis, a presumptive diagnosis of urinary tract obstruction with uroabdomen and hydronephrosis was reached. Abdominal radiographs did not assist in reaching an antemortem diagnosis. Postmortem examination confirmed a urinary bladder rupture secondary to urethral obstruction by a single urethrolith. Bilateral hydronephrosis and hydroureter were identified and determined to be a result of bilateral ureteroliths. Urolith analysis revealed a composition of 100% calcium carbonate. A dietary analysis was performed, implicating an increased Ca:P ratio from a food preparation miscommunication as a contributing factor. Appropriate husbandry changes were made, and mob surveillance procedures were performed, which resolved the urolithiasis risk for the remaining five animals.
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Carbonato de Calcio/química , Macropodidae , Cálculos Ureterales/veterinaria , Animales , Masculino , Radiografía , Cálculos Ureterales/química , Cálculos Ureterales/diagnóstico por imagenRESUMEN
A 16-yr-old male clouded leopard (Neofelis nebulosa) was presented for lethargy and anorexia. A cutaneous abdominal mass extending from the pubis to just caudal to the xiphoid process was present. A biopsy revealed histologic lesions consistent with an atypical mycobacterial infection consisting of diffuse, severe, pyogranulomatous dermatitis and panniculitis, with clear vacuoles and 3-5 microm, intravacuolar, faintly eosinophilic, filamentous bacilli that stained positively with FiteFaraco modified acid-fast stain. The clouded leopard had biochemical findings suggestive of chronic renal failure and euthanasia was elected. Histological evaluation of tissues collected at postmortem examination revealed multicentric B-cell lymphoma involving the oral cavity, liver, spleen, and multiple lymph nodes, bilateral testicular seminomas, thyroid follicular cell adenoma, thyroid C cell adenoma, and biliary cystadenomas. Bacterial culture and molecular sequencing identified the causative agent of the cutaneous abdominal mass as belonging to the Mycobacterium fortuitum group.
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Felidae , Infecciones por Mycobacterium no Tuberculosas/veterinaria , Enfermedades Cutáneas Bacterianas/veterinaria , Animales , Masculino , Infecciones por Mycobacterium no Tuberculosas/microbiología , Infecciones por Mycobacterium no Tuberculosas/patología , Mycobacterium fortuitum , Enfermedades Cutáneas Bacterianas/microbiología , Enfermedades Cutáneas Bacterianas/patologíaRESUMEN
Canine pituitary dwarfism in German Shepherd and related dog breeds has been reported to be associated with a 7-bp deletion mutation in intron 5 of the LHX3 gene. This mutation is transmitted as an autosomal recessive trait that results in dwarf dogs with significantly smaller stature and abnormal haircoat, and potentially early death. Phenotypically, affected adult dogs are proportionally dwarfs. These dwarfs also have a soft, woolly puppy coat that fails to transition into the typical adult hair coat, and marked hair loss occurs in some dogs. We report a similar manifestation of dwarfism in Tibetan Terriers with the same LHX3 mutation. Dwarf Tibetan Terrier puppies were born physically normal but failed to gain weight or to grow at the same rate as their normal littermates. The 7-bp deletion mutation of the LHX3 gene was identified in both alleles of 3 Tibetan Terrier dwarfs from 3 litters, which were biologically related. All parents of these dogs are carriers, confirming transmission of dwarfism in an autosomal recessive manner. Recognition and detection of this mutation will help in guiding future breeding plans to eventually eliminate this trait from Tibetan Terriers.
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Enfermedades de los Perros/genética , Enanismo Hipofisario/veterinaria , Proteínas con Homeodominio LIM/metabolismo , Factores de Transcripción/metabolismo , Animales , Perros , Enanismo Hipofisario/genética , Predisposición Genética a la Enfermedad , Proteínas con Homeodominio LIM/genética , Masculino , Mutación , Tibet , Factores de Transcripción/genéticaRESUMEN
Scedosporium apiospermum is an opportunistic mold that is an emerging disease in humans and animals. This report describes a case of S. apiospermum infection inciting a mural urinary bladder mass and focal peritonitis in a dog that had a history of multiple traumatic events several years prior. For diagnosis, culture followed by MALDI-ToF, PCR, and sequencing was performed to accurately identify the species. Susceptibility testing was also performed due to the inherent resistance of S. apiospermum to numerous antifungal agents.
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We diagnosed epitheliotropic T-cell lymphoma of the forestomachs in 2 aged, half-sibling, zoo-managed bontebok (Damaliscus pygargus pygargus). One bontebok also had mesenteric lymph node and cutaneous involvement. Both animals had a history of chronic abdominal distension and diminished body condition that resulted in euthanasia. At autopsy, both animals had marked ruminal distension with diffusely blunted ruminal papillae and reticular crests. In case 1, there was an increased amount and particle length of the ruminoreticular fibrous material with scant fluid, and a 2-cm diameter focus of cutaneous crusting adjacent to a mammary teat. In case 2, the rumen and reticulum were fluid-distended with decreased fibrous material. Histologically in case 1, the rumen, reticulum, omasum, and skin had intraepithelial nests and sheets of neoplastic small lymphocytes; in case 2, the rumen and reticulum had a similar neoplastic cell population. Immunohistochemically, neoplastic lymphocytes were immunoreactive for CD3 and negative for CD20, confirming the diagnosis of epitheliotropic T-cell lymphoma.
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Antílopes , Linfoma de Células T/veterinaria , Neoplasias Cutáneas/veterinaria , Neoplasias Gástricas/veterinaria , Animales , Femenino , Linfoma de Células T/diagnóstico , Masculino , Neoplasias Cutáneas/diagnóstico , Neoplasias Gástricas/diagnósticoRESUMEN
INTRODUCTION: Although hand temperature and electromyograph biofeedback have evidence for migraine prevention, to date, no study has evaluated heartrate variability (HRV) biofeedback for migraine. METHODS: 2-arm randomized trial comparing an 8-week app-based HRV biofeedback (HeartMath) to waitlist control. Feasibility/acceptability outcomes included number and duration of sessions, satisfaction, barriers and adverse events. Primary clinical outcome was Migraine-Specific Quality of Life Questionnaire (MSQv2). RESULTS: There were 52 participants (26/arm). On average, participants randomized to the Hearthmath group completed 29 sessions (SD = 29, range: 2-86) with an average length of 6:43 min over 36 days (SD = 27, range: 0, 88) before discontinuing. 9/29 reported technology barriers. 43% said that they were likely to recommend Heartmath to others. Average MSQv2 decreases were not significant between the Heartmath and waitlist control (estimate = 0.3, 95% CI = -3.1 - 3.6). High users of Heartmath reported a reduction in MSQv2 at day 30 (-12.3 points, p = 0.010) while low users did not (p = 0.765). DISCUSSION: App-based HRV biofeedback was feasible and acceptable on a time-limited basis for people with migraine. Changes in the primary clinical outcome did not differ between biofeedback and control; however, high users of the app reported more benefit than low users.
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Trastornos Migrañosos , Teléfono Inteligente , Biorretroalimentación Psicológica , Frecuencia Cardíaca , Humanos , Trastornos Migrañosos/terapia , Calidad de VidaRESUMEN
OBJECTIVE: To determine whether a smartphone application (app) with an electronic headache diary and a progressive muscle relaxation (PMR) intervention is feasible and acceptable to people presenting to the Emergency Department (ED) with migraine. METHODS: This single arm prospective study assessed feasibility by actual use of the app and acceptability by satisfaction with the app. We report preliminary data on change in migraine disability and headache days. RESULTS: The 51 participants completed PMR sessions on a mean of 13 ± 19 (0,82) days for the 90-day study period, lasting a median of 11 min (IQR 6.5, 17) each. Median number of days of diary use was 34 (IQR 10, 77). Diaries were completed at least twice a week in half of study weeks (337/663). Participants were likely (≥4/5 on a 5-point Likert scale) to recommend both the app (85%) and PMR (91%). MIDAS scores significantly decreased by a mean of 38 points/participant (p < 0.0001). More frequent PMR use was associated with a higher odds of headache free days (p = 0.0148). CONCLUSION: Smartphone-based PMR introduced to patients who present to the ED for migraine is feasible and acceptable. More frequent users have more headache free days. Future work should focus on intervention engagement.
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Trastornos Migrañosos , Teléfono Inteligente , Terapia Conductista , Servicio de Urgencia en Hospital , Humanos , Trastornos Migrañosos/terapia , Estudios ProspectivosRESUMEN
While the genetic contributions to the predisposition of Bernese mountain dogs (BMDs) to histiocytic sarcoma (HS) remains unclear, some insights into key genetic drivers have been gained. Our group recently reported a mutation in the PTPN11 gene (E76K). We have now identified a second missense mutation in PTPN11 (G503V), and a mutation in KRAS (Q61H) present in HS cell lines. These mutations are associated with malignancies in humans, and known to be gain-of-function mutations that result in activation of the mitogen-activated protein kinase (MAPK) pathway. The goal of the present study was to evaluate the prevalence of these mutations in a large sample of HS cases from BMDs and golden retrievers, and in lymphoma cases, from a cohort of BMDs. Mutations in PTPN11 were present in HS in 41/96 (43%) BMDs, and in 3/13 (23%) golden retrievers. PTPN11 mutations E76K and G503V did not coexist in the same neoplasm. The KRAS mutation was much less frequent, with a prevalence of 3.1% (3/96). We did not identify either PTPN11 nor KRAS mutations in any of the lymphoma samples. These results point out the potential relevance of PTPN11 and KRAS mutations as activators of the oncogenic MAPK pathway for canine HS, particularly in BMDs.
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Enfermedades de los Perros/genética , Perros/genética , Sarcoma Histiocítico/genética , Proteína Tirosina Fosfatasa no Receptora Tipo 11/genética , Proteínas Proto-Oncogénicas p21(ras)/genética , Animales , Femenino , Mutación con Ganancia de Función , Sistema de Señalización de MAP Quinasas , MasculinoRESUMEN
Canine histiocytic sarcoma is a highly aggressive and metastatic hematopoietic neoplasm that responds poorly to currently available treatment regimens. Our goal was to establish a clinically relevant xenograft mouse model to assess the preclinical efficacy of novel cancer treatment protocols for histiocytic sarcoma. We developed an intrasplenic xenograft mouse model characterized by consistent tumor growth and development of metastasis to the liver and other abdominal organs. This model represents the metastatic or disseminated form of canine histiocytic sarcoma, which is considered the most clinically challenging form of the disease. Transfection of tumor cells with a luciferase vector supported the use of in vivo bioluminescence imaging to track tumor progression over time and to assess the response of this murine model to novel chemotherapeutic agents. Dasatinib treatment of the mice with intrasplenic xenografts decreased tumor growth and increased survival times, compared with mice treated with vehicle only. Our findings indicate the potential of dasatinib for the treatment of histiocytic sarcoma in dogs and for similar diseases in humans. These results warrant additional studies to clinically test the efficacy of dasatinib in dogs with histiocytic sarcoma.
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Dasatinib/uso terapéutico , Modelos Animales de Enfermedad , Enfermedades de los Perros/tratamiento farmacológico , Sarcoma Histiocítico/veterinaria , Animales , Antineoplásicos/uso terapéutico , Enfermedades de los Perros/diagnóstico por imagen , Perros , Xenoinjertos , Sarcoma Histiocítico/diagnóstico por imagen , Sarcoma Histiocítico/tratamiento farmacológico , RatonesRESUMEN
Histiocytic sarcoma in humans is an aggressive orphan disease with a poor prognosis as treatment options are limited. Dogs are the only species that spontaneously develops histiocytic sarcoma with an appreciable frequency, and may have value as a translational model system. In the current study, high-throughput drug screening utilizing histiocytic sarcoma cells isolated from canine neoplasms identified these cells as particularly sensitive to a MEK inhibitor, trametinib. One of the canine cell lines carries a mutation in PTPN11 (E76K), and another one in KRAS (Q61H), which are associated with the activation of oncogenic MAPK signaling. Both mutations were previously reported in human histiocytic sarcoma. Trametinib inhibited sensitive cell lines by promoting cell apoptosis, indicated by a significant increase in caspase 3/7. Furthermore, in vitro findings were successfully recapitulated in an intrasplenic orthotopic xenograft mouse model, which represents a disseminated aggressive form of histiocytic sarcoma. Mice with histiocytic sarcoma xenograft neoplasms that were treated with trametinib had significantly longer survival times. Target engagement was validated as activity of ERK, downstream of MEK, was significantly downregulated in neoplasms of treated mice. Additionally, trametinib was found in plasma and neoplastic tissues within projected therapeutic levels. These findings demonstrate that in dogs, histiocytic sarcoma may be associated with a dysfunctional MAPK pathway, at least in some cases, and may be effectively targeted through MEK inhibition. Clinical trials to test safety and efficacy of trametinib in dogs with histiocytic sarcoma are warranted, and may provide valuable translational information to similar diseases in humans. Mol Cancer Ther; 17(11); 2439-50. ©2018 AACR.