Recently, histologic subtypes of oral squamous cell carcinoma (SCC) corresponding to the human classification scheme have been proposed for dogs. A papillary squamous cell carcinoma subtype is characterized by dominant exophytic architectural growth with limited invasion, a lower metastatic rate, and better overall survival compared with conventional SCC. Whereas most canine oral conventional SCCs are easily diagnosed by histologic examination, the diagnosis of canine oral papillary squamous cell carcinoma (COPSCC) can be challenging since the exophytic portion lacks histologic features of malignancy and appears similar to oral nonviral papillomas. In contrast, the invasive portion of COPSCC has morphologic similarities to conventional SCC and canine acanthomatous ameloblastoma. The goals of this study were to immunophenotype these 3 entities and to potentially identify discriminating markers. A panel of 17 immunohistochemical markers was investigated in tissue microarrays that included 25 COPSCCs, 10 conventional SCCs, and 10 canine acanthomatous ameloblastomas. Additionally, COPSCCs were screened for papillomavirus as a potential cause using immunohistochemistry and in situ hybridization. COPSCC had immunophenotypical similarities with conventional SCC and acanthomatous ameloblastoma, but the combined differences in immunolabeling for AE1/AE3, 34βE12, p63, and calretinin discriminated between the entities. Papillomavirus was not detected in any COPSCC, making a viral pathogenesis unlikely. A better understanding of the immunophenotype of COPSCC will aid in a more accurate diagnosis and potentially improve therapeutic approaches.

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.

MAPK has been reported as a key oncogenic pathway for canine histiocytic sarcoma, which can be pharmacologically targeted with trametinib, a small inhibitor of MEK1/2. Preliminary data showed promising antitumor activity in in vitro and in vivo models and represented a proof of concept to translate the findings from bench to bedside. In this phase I, dose escalating study using a 3 + 3 cohort design, trametinib was evaluated in 18 dogs with cancer. Adverse events were graded according to VCOG‐CTCAE v2. Blood samples and tumour biopsies were collected for pharmacokinetic and pharmacodynamic assessment. Trametinib was well tolerated with a maximum tolerated dose of 0.5 mg/m²/day, PO. Dose‐limiting toxicities included systemic hypertension, proteinuria, lethargy and elevated ALP, and were all Grade 3. The drug exposures increased more than linearly with dose since the elimination of trametinib was saturable. At a dose of 500 μg Q24h (0.5 mg/m²/day in a 30 kg dog), approximately 70% of dogs had an average steady‐state concentration of 10 ng/mL, achieved after approximately 2 weeks. This threshold was associated with clinical efficacy in humans. Target engagement was not observed in biospecimens collected on Days 0 and 7. In conclusion, trametinib was considered safe in dogs with cancer, and the dose of 0.5 mg/m²/day was the recommended dose for phase II studies.

Tetranucleotide and pentanucleotide short tandem repeat (hereafter termed tetraSTR and pentaSTR) polymorphisms have properties that make them desirable for DNA profiling and paternity testing. However, certain species, such as the horse, have far fewer tetraSTRs than other species and for this reason dinucleotide STRs (diSTRs) have become the standard for DNA profiling in horses, despite being less desirable for technical reasons. During our testing of a series of candidate genes as potentially underlying a heritable condition characterized by megaesophagus in the Friesian horse breed, we found that good tetraSTRs do exist in horses but, as expected, at a much lower frequency than in other species, e.g., dogs and humans. Using a series of efficient methods developed in our laboratory for the production of multiplexed tetraSTRs in other species, we identified a set of tetra- and pentaSTRs that we developed into a 17-plex panel for the horse, plus a sex-identifying marker near the amelogenin gene. These markers were tested in 128 horses representing 16 breeds as well as crossbred horses, and we found that these markers have useful genetic variability. Average observed heterozygosities (Ho) ranged from 0.53 to 0.89 for the individual markers (0.66 average Ho for all markers), and 0.62-0.82 for expected heterozygosity (He) within breeds (0.72 average He for all markers). The probability of identity (PI) within breeds for which 10 or more samples were available was at least 1.1 x 10⁻¹¹, and the PI among siblings (PIsib) was 1.5 x 10⁻⁵. Stutter was ≤ 11% (average stutter for all markers combined was 6.9%) compared to the more than 30% typically seen with diSTRs. We predict that it will be possible to develop accurate allelic ladders for this multiplex panel that will make cross-laboratory comparisons easier and will also improve DNA profiling accuracy. Although we were only able to exclude candidate genes for Friesian horse megaesophagus with no unexcluded genes that are possibly causative at this point in time, the study helped us to refine the methods used to develop better tetraSTR multiplexed panels for species such as the horse that have a low frequency of tetraSTRs.

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.