One of the primary objectives of the Oncology Pathology Working Group (OPWG) is for oncologists and pathologists to collaboratively generate consensus documents to standardize aspects of and provide guidelines for veterinary oncologic pathology. Consensus is established through review of relevant peer‐reviewed literature relative to a subgroup's particular focus. In this article, the authors provide a critical review of the current literature for the diagnosis of, and histopathologic prognostication for, canine cutaneous and oral/lip melanocytic neoplasms, suggest guidelines for reporting, provide recommendations for clinical interpretation, and discuss future directions. This document represents the opinions of the working group and the authors and does not constitute a formal endorsement by the American College of Veterinary Pathologists, American College of Veterinary Internal Medicine or the Veterinary Cancer Society.

A 5-year-old neutered male Beagle mix dog had a 5-day history of generalized tonic-clonic seizures. Before the seizures, the dog had a 1-2-month history of progressive right hemiparesis. In computed tomography images, a presumed extraaxial mass with hyperostosis and destruction of the skull covering the mass were identified. Surgical excision was performed and the histopathologic diagnosis was meningioma. Hyperostosis is frequently associated with feline meningioma, but this report documents that hyperostosis may also occur secondary to meningioma in the dog.

Marginal zone lymphoma (MZL) and mantle cell lymphoma (MCL) belong to a subgroup of indolent B-cell lymphomas most commonly reported in the canine spleen. The goal of this study was to characterize the immunophenotype of splenic MZL and MCL in comparison to their human counterparts. Ten MCLs and 28 MZLs were selected based on morphology. A tissue microarray was generated, and expression of CD3, CD5, CD10, CD45, CD20, CD79a, Pax-5, Bcl-2, Bcl-6, cyclin D1, cyclin D3, MCL-1, MUM-1, and Sox-11 was evaluated. Neoplastic cells in all MCLs and MZLs were positive for CD5, CD20, CD45, CD79a, and BCL2 and negative for CD3, CD10, Bcl-6, cyclin D1, and cyclin D3. Positive labeling for Pax-5 was detected in 8 of 10 MCLs and 26 of 28 MZLs. Positive labeling for MUM-1 was detected in 3 of 10 MCLs, and 27 of 28 MZLs were positive for MUM-1. No MCLs but 8 of 24 MZLs were positive for MCL-1. Canine splenic MZL and MCL have a similar immunophenotype as their human counterparts. However, human splenic MCL overexpresses cyclin D1 due to a translocation. A similar genetic alteration has not been reported in dogs. In addition, in contrast to human MZL, canine splenic MZL generally expresses CD5. Following identification of B vs T cells with CD20 and CD3, a panel composed of BCL-2, Bcl-6, MUM-1, and MCL-1 combined with the histomorphological pattern can be used to accurately diagnose MZL and MCL in dogs. Expression of Bcl-2 and lack of MCL-1 expression in MCL may suggest a therapeutic benefit of BCL-2 inhibitors in canine MCL.

T-zone lymphoma (TZL) is an indolent nodal T-cell lymphoma most commonly observed in submandibular lymph nodes in dogs. The diagnosis is based on its distinct morphology and expression of CD3. TZL has been reported to have a low Ki67 index and to lack expression of CD45. The latter feature has been used to diagnose this type of lymphoma via fine needle aspirate and flow cytometry without confirmation of the characteristic tissue architecture. The goal of this study was to characterize the immunophenotype of canine nodal TZL in greater detail. Twenty-seven TZLs were selected based on their characteristic morphology. A tissue microarray was generated, and immunohistochemical expression of CD3, CD5, CD20, CD21, CD25, CD45, Bcl-6, and Ki67 was evaluated. Neoplastic T cells in all cases were positive for CD3, CD5, and CD25, and negative for CD20, CD21, and Bcl-6. Positive labelling for CD45 was detected in 2 of the 27 cases with the remaining 25 cases being negative. All cases had a low Ki67 index with an average index of 19.56%. For the CD45-positive TZLs, clonality of the T-cell antigen receptor gamma gene was confirmed in only one of these cases. The observed immunophenotype of canine TZL is similar to previous publications with the exception that 2 cases expressed CD45. Expression of CD45 in TZLs in this study emphasizes the importance of interpreting immunophenotypic findings in conjunction with histopathology to reach an accurate diagnosis and not to use lack of expression of a particular antigen as the sole diagnostic criterion.

A clinically normal 30-year-old female rhesus macaque (Macaca mulatta) was acquired from the Harlow Primate Laboratory at the University of Wisconsin in Madison. In 1959, the macaque, then approximately 1 year old, arrived at the Harlow Laboratory where she gave birth to eight infants between 1964 and 1979. She was maintained at Harlow in either a nuclear family (one mate and offspring) or in single-caged housing and received a standard diet of Purina Monkey Chow with occasional fruit. Subsequent to acquisition by the Division of Comparative Medicine at Johns Hopkins University, she was euthanatized as a normal control in a study on aging.Gross examination revealed numerous diverticula randomly distributed along the length of the large intestine. These contained fecal material superficially in their lumina, with deeper, greenish-white solid cores (fecoliths). There was also a small, firm, 75 mm homogeneous tan colonic mass near the ileocecocolic junction that appeared to wrap around the wall of the colon and merge imperceptibly with the colonic musculature. It was unassociated with t e diverticula. Other gross findings included valvular endocar 'osis and pulHistologically, the diverticula were lined by normal-appearing but compressed colonic epithelium with a moderate nonsuppurative lamina proprial infiltrate. The walls of the diverticula were partially or totally absent of muscular layers at their deepest borders (Fig. 1); the muscularis mucosa and submucosal tissues abutted directly onto the peritoneal fat. The luminal cores consisted of a laminated hyalinized material without cellular definition near the epithelial border, with more superficial fecal material and mixed colonies of bacteria. The colonic mass (Fig. 2) consisted of a homogeneous population of spindle shaped cells arranged in interlacing, disorganized dense bundles or sheets that palisaded around the circumference of one bowel loop, directly abutting on the muscularis mucosa (Figs. 2, 3). There were also areas where tumor cells penetrated the muscularis mucosa and infiltrated the lamina propria. The cells had plump, vesicular, round to elongated nuclei, often with blunted, squarish ends, and multiple small nucleoli. Occasional enlarged and multinucleated cells were seen. Cell borders were indistinct but cytoplasm provided a eosinophilic background. Stroma was minimal. Mitotic figures were present but uncommon. With Masson's trichrome, the tumor cells were red, and with phosphotungstic acid hematoxylin they were muddy blue. No striations were observed. There was no evidence of vascular invasion or metastasis. monary anthracosis.