Cancer registries are important tools for cancer surveillance. The status of veterinary cancer registries was reviewed at a meeting in Oslo in 2010 1 and also discussed during an ESVONC (European Society of Veterinary Oncology) meeting in Lyon, France, in May 2017. 2 In general, existing veterinary cancer registries suffer from lack of standardization, communication and means of comparison. Therefore, international efforts and networking are required to connect registries worldwide and generate reliable global findings. The idea of creating a global system to register animal cancers arose during the 3rd World Veterinary Cancer Congress, held in Foz do Iguaçu, PR, Brazil, in May 2016, as an input by the late Johan de Vos, from the Netherlands.

Oral mucosal melanoma (OMM) is the most common oral cancer in dogs and is very aggressive in this species; its risk factors and etiology are yet to be determined. This study aimed to unravel the risk factors for the development of OMM in dogs and to investigate the possible presence of papillomaviruses as an etiological factor. A case-control study was conducted in 15 dogs with OMM and 15 paired controls whose owners answered an epidemiological questionnaire. Oral swabs from the same dogs were subjected to 16S rRNA sequencing for microbiome analyses. In addition, DNA fragments of OMM had their DNA extracted and amplified by polymerase chain reaction in an attempt to detect canine papillomaviruses. The gingiva was the most frequent anatomical site (47%) of OMM, and most tumors were stage III when diagnosed. Most dogs bearing OMM and the controls had grade 3 periodontal disease, and this factor, along with tartar treatment and tooth brushing, did not differ between cases and controls. Most dogs with OMM and most controls had contact with smokers; there was no statistically significant difference. Canine papillomaviruses were not detected among OMM cases. Tannerella forsythia and Porphyromonas gingivalis were significantly increased in case dogs compared to the controls. As these bacteria are reportedly involved in the pathogenesis of periodontal disease and esophageal cancer in humans, we suggest that they might be risk factors for the development of canine OMM. The limitations of this study include the low number of dogs, and therefore, further studies on canine OMM with larger numbers of animals are encouraged.

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