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Cutaneous round cell neoplasms (RCNs) are among the most common skin tumors of dogs. Although a diagnosis can be made in most cases following the examination of H&E-stained routine samples, less-differentiated neoplasms can exhibit overlapping morphologic features that may be challenging to the pathologist, and require immunohistochemistry or molecular testing to reach a final diagnosis. Many patients with cutaneous RCNs are initially seen by a general practitioner and are not referred to a veterinary teaching hospital until a diagnosis has been made. For this reason, anatomic pathology residents at some academic or other training institutions may not be exposed frequently to RCNs during the surgical biopsy service as part of their residency training. In an attempt to fill that gap, here we review the key routine histologic features of canine cutaneous RCNs.

Cutaneous and mucocutaneous plasmacytoma (PCT) is a common neoplasm of dogs. Tumors can be single or multiple and occur predominantly in the oral cavity, lip, ears, digits, and trunk. Although these tumors typically offer no diagnostic challenge for the pathologist, subsets of PCTs with atypical morphologic configurations may make differentiation from other neoplasms difficult. We describe 6 cases of canine cutaneous and mucocutaneous PCT with pseudoglandular arrangement of neoplastic cells. The mean age of affected dogs was 11.3 y, and multiple breeds and sites were affected. Histologically, neoplastic cells were arranged in sheets, packets, and pseudoglandular structures containing central accumulations of blood or eosinophilic material admixed with neoplastic cells and hemosiderin-laden macrophages. Given the presence of pseudoglandular structures resembling neoplastic acini, epithelial neoplasia was occasionally included in the differential diagnosis. Neoplastic cells were strongly immunopositive for multiple myeloma oncogene 1 ( MUM-1) and immunonegative for pancytokeratin AE1/AE3. Canine cutaneous and mucocutaneous PCTs with pseudoglandular morphology may resemble epithelial neoplasia and raise questions about tumor histogenesis.

Rhodococcus equi is an important pathogen of foals that causes severe pneumonia. To date, there is no licensed vaccine effective against R. equi pneumonia of foals. The objectives of our study were to develop an electron beam (eBeam) inactivated vaccine against R. equi and evaluate its immunogenicity. A dose of eBeam irradiation that inactivated replication of R. equi while maintaining outer cell wall integrity was identified. Enteral administration of eBeam inactivated R. equi increased interferon-γ production by peripheral blood mononuclear cells in response to stimulation with virulent R. equi and generated naso-pharyngeal R. equi-specific IgA in newborn foals. Our results indicate that eBeam irradiated R. equi administered enterally produce cell-mediated and upper respiratory mucosal immune responses, in the face of passively transferred maternal antibodies, similar to those produced in response to enteral administration of live organisms (a strategy which previously has been documented to protect foals against intrabronchial infection with virulent R. equi). No evidence of adverse effects was noted among vaccinated foals.