Currently, prognostic and therapeutic determinations for canine cutaneous mast cell tumors (MCTs) are primarily based on histologic grade. However, the use of different grading systems by veterinary pathologists and institutional modifications make the prognostic value of histologic grading highly questionable. To evaluate the consistency of microscopic grading among veterinary pathologists and the prognostic significance of the Patnaik grading system, 95 cutaneous MCTs from 95 dogs were

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Neoplastic diseases are typically diagnosed by biopsy and histopathological evaluation. The pathology report is key in determining prognosis, therapeutic decisions, and overall case management and therefore requires diagnostic accuracy, completeness, and clarity. Successful management relies on collaboration between clinical veterinarians, oncologists, and pathologists. To date there has been no standardized approach or guideline for the submission, trimming, margin evaluation, or reporting of neoplastic biopsy specimens in veterinary medicine. To address this issue, a committee consisting of veterinary pathologists and oncologists was established under the auspices of the American College of Veterinary Pathologists Oncology Committee. These consensus guidelines were subsequently reviewed and endorsed by a large international group of veterinary pathologists. These recommended guidelines are not mandated but rather exist to help clinicians and veterinary pathologists optimally handle neoplastic biopsy samples. Many of these guidelines represent the collective experience of the committee members and consensus group when assessing neoplastic lesions from veterinary patients but have not met the rigors of definitive scientific study and investigation. These questions of technique, analysis, and evaluation should be put through formal scrutiny in rigorous clinical studies in the near future so that more definitive guidelines can be derived.

(1) Histopathological lesions do not reliably differentiate EM, SJS and TEN. (2) A multicentre study to develop a consensus set of clinical criteria for EM and SJS/TEN in animals is overdue. (3) No adjunctive therapies, including intravenous immunoglobulin and ciclosporin, have met evidence-based standards.

Histologic grading schemes for canine cutaneous mast cell tumors (MCTs) were not developed for subcutaneous MCTs. Despite this, subcutaneous MCTs are currently categorized by many as grade II or higher. The aim of this investigation was to assess the pathology and clinical outcome for subcutaneous MCTs to provide a more accurate prognosis. Information on clinical outcome for 306 dogs was obtained from veterinarians and correlated with histologic features. Mean and median follow-up was 842 and 891 days, respectively (range, 3-2,305 days). Only 27 (9%) were confirmed as mast cell-related deaths. Metastasis occurred in 13 (4%), and 24 (8%) had local reoccurrence, even though 171 (56%) cases had incomplete surgical margins. Median survival time was not reached, and the estimated 6-month, 1-, 2-, and 5-year survival probabilities were 95%, 93%, 92%, and 86%, respectively. Dogs were euthanized or died as a result of local tumor reoccurrence, additional MCT development distant to the surgical site, or metastasis. Decreased survival time was linked to mitotic index (number of mitotic figures per 10 high-power fields), infiltrative growth pattern, and presence of multinucleation. Both univariable and multivariable analysis showed mitotic index to be strongly predictive of survival, local reoccurrence, and metastasis. The results of the study indicate that the majority of subcutaneous MCTs have a favorable prognosis, with extended survival times and low rates of reoccurrence and metastasis.

Idiosyncratic drug reactions are difficult to study in humans due to their unpredictability. Unfortunately, this characteristic also hinders the development of animal models needed for mechanistic studies. Nevirapine, used to treat human immunodeficiency virus (HIV) infections, results in a severe idiosyncratic skin rash in some patients. We found that nevirapine can also cause a significant rash in some strains of rats. At a dose of 150 mg/kg/day, the incidence in female Sprague-Dawley rats was 6/28 (21%), in female Brown Norway rats 32/32 (100%), and in female Lewis rats 0/6 (0%) while no male Sprague-Dawley or Brown Norway rats developed a rash. Female SJL mice 0/7 also did not develop nevirapine-induced skin lesions. The first sign of a reaction in Brown Norway rats was red ears at days 7-10 followed by a rash with scabbing mainly on the back; this was a shorter time to onset than in Sprague-Dawley rats. Light microscopy of the skin revealed a primarily mononuclear inflammatory infiltrate and lesions typical of self-trauma. Immunohistochemistry results suggest that the infiltrate was composed of CD4 and CD8 T cells as well as macrophages. A lower dose of either 40 or 75 mg/kg/day did not lead to a rash and, in fact, 2 weeks of the lower doses induced tolerance to the 150 mg/kg/day dose in female Brown Norway rats. A dose of 100 mg/kg/day resulted in rash in 2/4 (50%) of female Brown Norway rats. Rechallenge of Brown Norway rats that had been allowed to recuperate after a nevirapine-induced rash led to red ears in less than 24 h followed by hair loss and occasional skin lesions. Although the skin rash was less evident on rechallenge, microscopically, the cellular infiltrate was more prominent, especially surrounding the hair follicles. Moreover, there were lesions of interface dermatitis with apoptosis and satellitosis, indicative of a cell-mediated immune attack on the epidermis. While systemic signs of illness did not accompany the rash on primary exposure, on rechallenge, the animals appeared generally unwell and this forced sacrifice after 2 weeks or less of treatment. Importantly, splenocytes isolated from rechallenged animals were able to transfer susceptibility to nevirapine-induced skin rash to naïve female Brown Norway recipients, which was illustrated by a faster time to onset of rash in the recipients. The characteristics of this adverse reaction are similar to that seen in humans; that is, it is idiosyncratic in that it only occurs in some strains of animals, is delayed in onset, is more common in females, is dose-dependent, and appears to be immune-mediated. Therefore, it may represent a good animal model for the study of idiosyncratic drug reactions.

Rhodococcus equi is a facultative intracellular pathogen of macrophages and a cause of pneumonia in young horses (foals) and immunocompromised people. Isolates of R. equi from pneumonic foals typically contain large, 85- or 90-kb plasmids encoding a highly immunogenic virulence-associated protein (VapA). The objective of this study was to determine the role of the 85-kb plasmid and VapA in the intracellular survival and virulence of R. equi. Clinical isolates containing the plasmid and expressing VapA efficiently replicated within mouse macrophages in vitro, while plasmid-cured derivatives of these organisms did not multiply intracellularly. An isolate harboring the large plasmid also replicated in the tissues of experimentally infected mice, whereas its plasmid-cured derivative was rapidly cleared. All foals experimentally infected with a plasmid-containing clinical isolate developed severe bronchopneumonia, whereas the foals infected with its plasmid-cured derivative remained asymptomatic and free of visible lung lesions. By day 14 postinfection, lung bacterial burdens had increased considerably in foals challenged with the plasmid-containing clinical isolate. In contrast, bacteria could no longer be cultured from the lungs of foals challenged with the isogenic plasmid-cured derivative. A recombinant, plasmid-cured derivative expressing wild-type levels of VapA failed to replicate in macrophages and remained avirulent for both mice and foals. These results show that the 85-kb plasmid of R. equi is essential for intracellular replication within macrophages and for development of disease in the native host, the foal. However, expression of VapA alone is not sufficient to restore the virulence phenotype.

There is an increasing need for more accurate prognostic and predictive markers in veterinary oncology because of an increasing number of treatment options, the increased financial costs associated with treatment, and the emotional stress experienced by owners in association with the disease and its treatment. Numerous studies have evaluated potential prognostic and predictive markers for veterinary neoplastic diseases, but there are no established guidelines or standards for the conduct and reporting of prognostic studies in veterinary medicine. This lack of standardization has made the evaluation and comparison of studies difficult. Most important, translating these results to clinical applications is problematic. To address this issue, the American College of Veterinary Pathologists' Oncology Committee organized an initiative to establish guidelines for the conduct and reporting of prognostic studies in veterinary oncology. The goal of this initiative is to increase the quality and standardization of veterinary prognostic studies to facilitate independent evaluation, validation, comparison, and implementation of study results. This article represents a consensus statement on the conduct and reporting of prognostic studies in veterinary oncology from veterinary pathologists and oncologists from around the world. These guidelines should be considered a recommendation based on the current state of knowledge in the field, and they will need to be continually reevaluated and revised as the field of veterinary oncology continues to progress. As mentioned, these guidelines were developed through an initiative of the American College of Veterinary Pathologists' Oncology Committee, and they have been reviewed and endorsed by the World Small Animal Veterinary Association.