Every time, more cases of dogs with tumors are receiving in the veterinary clinics and in the Laboratories of Diagnosis. This suggests that the casuistry of tumors is increasing as well as the early appearance of tumors in dogs. In the valley of Toluca, it lacks of epidemic data in veterinary oncology.

Here, we wanted to know the breeds, ages, sexes, affected tissues and types of tumors in dogs, besides beginning to establish a bank of tissues for later studies on some mutations that could be associated to some types of tumors. Here the clinical-pathological data of the dogs affected that were remitted to the Center of Investigation and Advanced Studies in Animal Health (CIESA)-FMVZ-UAEM in Toluca city, from the year 2000 at the 2004 are discussed. All remitted samples were fixed during 24hr in 10% buffered formalin, tissues were included in paraffin, cut at 6µm thickness and stained with haematoxylin-eosin (HE) and with special colorations (Masson's, PAS and Von Kossa) according to the tumor type. All neoplasms were examined by histopathology and classified according to the WHO's International Histological Classification and to the Armed Forces Institute of Pathology.

Of a total of 46 studied samples, 32 (69.6%) were observed in females, 14 (30.4%) in males, 8 (17.4%) in animals until a year of age, 15 (32.6%) in two to six years-old animals, and 23 (50%) in animals from seven to fourteen years-old. The breeds affected more frequently remitted were the German Shepherd and the Labrador. According to the occurrence sites, there were 14 (30.4%) mammary tumors, 20 (43.5%) skin tumors, 5 (10.9%) reproductive tumors, 2 (4.3%) digestive (1 in liver and 1 in colon), 1 (2.2%) lymphoid (spleen), 1 (2.2%) bone tumor, besides 3 (6.5%) where the origin was not known. Of all tumors, 18 were maligns and 25 benign. The most frequently diagnosed tumor was the carcinoma followed by the fibroma.

These results demonstrate that the occurrence of tumors in dogs is not uncommon pathology and that the frequency is possibly to the rise. Also the occurrence of tumors in young dogs is frequent and it suggests the possibility that, the risk factors are showing up to an earlier age. It is important to continue this kind of studies to know more about the risk factors in pets and to compare them with those factors in the public health.