Abstract. In horses, osteosarcoma is a rare tumor, with the majority of reported cases occurring in the head, and, more specifically, in the mandible of young horses. The following report documents 8 cases of equine osteosarcoma, the majority occurring in male horses aged 7 years or older with a lack of metastasis identified in any horse. Six arose in the maxilla or mandible and one in the proximal tibia. The predominant subtype was fibroblastic osteosarcoma with fewer osteoblastic type tumors. All had osteoid and most had a chondromucinous matrix. Surgical excision was attempted in the majority of cases. An inability to completely excise the tumor and progressive disease typically resulted in euthanasia. To the authors' knowledge, this case series also documents the first report of an equine extraosseous osteosarcoma within the subcutaneous tissue caudal to the shoulder. Surgical excision appears successful with no recurrence of disease 14 months later. Further investigations of equine osteosarcoma and various chemotherapeutic agents are warranted to present additional treatment options.

Canine and human osteosarcoma (OSA) have many similarities, with the majority of reported cases occurring in the appendicular skeleton, gender predominance noted, high rate of metastasis at the time of presentation, and a lack of known etiology for this devastating disease. Due to poor understanding of the molecular mechanisms underlying OSA, we have characterized seven different OSA canine cell lines: Abrams, D17, Grey, Hughes, Ingles, Jarques, and Marisco and compared them to U2, a human OSA cell line, for the following parameters: morphology, growth, contact inhibition, migrational tendencies, alkaline phosphatase staining, heterologous tumor growth, double-strand DNA breaks, and oxidative damage. All results demonstrated the positive characteristics of the Abrams cell line for use in future studies of OSA. Of particular interest, the robust growth of a subcutaneous tumor and rapid pulmonary metastasis of the Abrams cell line in an immunocompromised mouse shows incredible potential for the future use of Abrams as a canine OSA model. Further investigations utilizing a canine cell model of OSA, such as Abrams, will be invaluable to understanding the molecular events underlying OSA, pharmaceutical inhibition of metastasis, and eventual prevention of this devastating disease.

Unlike seminomas in humans, seminomas in animals are not typically sub-classified as classical or spermatocytic types. To compare testicular germ cell tumours (TGCT) in dogs with those of men, archived tissues from 347 cases of canine testicular tumours were morphologically evaluated and characterized using human classification criteria. Histopathological and immunohistological analysis of PLAP, KIT, DAZ and DMRT1 expression revealed that canine seminomas closely resemble human spermatocytic seminomas. In addition, a relatively frequent concomitant presence of somatic cell tumours was noted in canine TGCT. None of the canine TGCT evaluated demonstrated the presence of carcinoma in situ cells, a standard feature of human classical seminomas, suggesting that classical seminomas either do not occur in dogs or are rare in occurrence. Canine spermatocytic seminomas may provide a useful model for this rare human neoplasm.

The results of this investigation support previous studies on the benefit of polylactide film barriers, like Lactosorb, for reducing peridural adhesion following spinal surgery. The performance of Mesofol in this investigation suggests that it may provide improved antiadhesion properties in comparison to the polylactide products. Safety issues related to impaired dural healing was not identified in either product.

Oesophageal leiomyosarcoma has yet to be reported in dogs. This retrospective case series describes the case management and clinical outcome of four dogs with oesophageal leiomyosarcoma treated by marginal excision alone. Histological features used to determine tumour grade included capsular invasion, percent necrosis, pleomorphism and mitotic rate. All tumours were designated grade 1 leiomyosarcoma. Excision of all grossly evident tumour tissue was achieved in two of the four cases; however, histopathologic evaluation showed tumour cells at the surgical margins in one of these two cases. Two dogs had grossly incomplete excision. Two dogs died from unrelated conditions, one 3 years and 5.5 months after surgery, the other at 65 days. One dog had persistent mega-oesophagus and was lost to follow-up 388 days after surgery and one dog is still alive (last follow-up 405 days after surgery). Despite large tumour size and incomplete excision, surgical removal of low-grade leiomyosarcomas can result in long-term resolution of clinical signs.