The study of cutaneous melanomas in Camargue-type gray-skinned horses (2): epidemiological survey

An epidemiological survey was made on cutaneous melanomas occurring in Camargue-type, gray-skinned horses in southern France. The population investigated was composed of 264 horses, which were selected from the Camargue horse stud registry and were allowed to be examined by the owners. The presence of tumors was inspected macroscopically according to the standardized protocols of veterinary medicine specialists, and some tumors were subjected to macroscopic histopathological examination. The results indicated that: 1) the prevalence of melanomas in the overall population was 31.4%; 2) the odds ratio was obtained for an age class of 5-9 years, in which most melanomas were presumed to occur; 3) the incidence of melanomas was significantly correlated with age, giving a prevalence of 67% at ages > 15 years; 4) the size and number of tumorous lesions were significantly related to age; 5) little correlation was observed between melanoma incidence and gender; and 6) the most frequently occurring body site of these tumors was underneath the tail. Because of their frequent occurrence in shaded body regions, sun exposure was not likely to be a risk factor for melanoma formation in these horses. In view of the slightly darker skin pigmentation in these horses at younger ages, the unique characteristics of their melanocytes may be associated with melanoma formation.