Osteosarcoma is the most common malignant bone tumor in dogs and, like its human orthologue, is characterized by aggressive local behavior and high metastatic rates. The Scottish deerhound is a breed of dog with a >15% incidence of osteosarcoma and represents an excellent spontaneously occurring large-animal model of the human disease. We modeled the transmission of the osteosarcoma phenotype in a population of over 1000 related deerhounds ascertained as part of a prospective health study. Variance component analysis, segregation analysis, and linear modeling were performed to evaluate heritability, to infer the presumptive transmission model, and to identify covariate effects for this phenotype within the breed, respectively. Based on variance component analysis, heritability (h2) was estimated to be 0.69. Six transmission models were analyzed by segregation analysis; based on Akaike's information criteria, the most parsimonious model was the Mendelian major gene model with dominant expression. Linear modeling identified gender and genotype as significant predictors of disease outcome. Importantly, duration of gonadal hormone exposure, weight, and height at maturity were not significant predictors of outcome. Inheritance of the putative high-risk allele was thus associated with >75% risk of disease occurrence compared to the <5% baseline risk. These results support the hypothesis that a major gene with a dominant effect explains most of the osteosarcoma phenotype within the Scottish deerhound.

A 14‐month‐old, entire, deerhound bitch experienced episodes of abdominal discomfort. During some episodes, the abnormally shaped spleen could be palpated in the dorsocaudal abdomen, rather than in its normal cranioventral location. Exploratory laparotomy revealed an enlarged spleen that was twisted on its long axis but not on its suspensory ligaments. The spleen was excised, and the dog made an uneventful recovery. To the best of our knowledge, this is the first report of a so‐called wandering spleen in a dog, a condition that has been described in humans, albeit rarely. This also is the first report of a twisted spleen in a dog. Veterinary practitioners should include these two possibilities (wandering spleen and twisted spleen) in their list of differential diagnoses when presented with a dog experiencing abdominal discomfort or with an abdominal mass.