Breed and Age as Risk Factors for Canine Mammary Tumours

Zatloukal J . , J . Lorenzová, F. Tich ̆, A. Neãas, H. Kecová, P. Kohout: Breed and Age as Risk Factors for Canine Mammary Tumours. Acta Vet. Brno 2005, 74: 103-109. Mammary tumours in 214 dogs were evaluated at the Department of Surgery and Orthopaedics, Veterinary and Pharmaceutical University Brno, between 1997 and 2001. Lesions of the mammary gland were classified as dysplasia/hyperplasia, benign and malignant tumours in 19, 61 and 134 patients, respectively. When there were different lesions of the mammary gland in one individual, the patient was classified according to the most malignant one. The above-mentioned patients were compared to the population of 17 053 dogs treated during the same period to determine age and breed predisposition. Considering the lesions of the mammary gland, the highest relative risk of dysplasia/hyperplasia, benign tumours and malignant tumours was at the age of 8, 10 and 13 years, respectively. Our results thus confirm the previous studies stating the highest incidence after 10 years of age. Poodles, English Cocker Spaniels and Dachshunds had a statistically significant relative risk developing benign and malignant tumours of the mammary gland (χ2-test, p < 0.01), confirming conclusions of previous studies concerning these breeds. We did not, however, prove higher relative risk in Irish Setters, Labrador Retrievers and Boxers. Breast neoplasms, histopathology, incidence, predisposition, retrospective study The mammary gland belongs to body areas with the highest incidence of neoplasia. Tumours of the mammary gland in female dogs represent up to 42% of all tumours (Johnson 1993; Dorn et al. 1968). They occur with much higher incidence than in other females of domestic animals and women (Brodey et al. 1983; Schneider 1970). Risk factors associated with the increased occurrence of mammary tumours in female dogs have already been studied. Higher incidence was found after the 6th year of age with the maximum being 9 to 11 years. Female dogs younger than 2 years were rarely affected (Schneider 1970; Brodey et al. 1983). Increased incidence of mammary tumours was found in many large as well as smaller breeds of dogs. The lowest occurrence was found in mongrels, Boxers and Chihuahuas (Dorn et al. 1968; Brodey et al. 1983; Cohen et al. 1974). Spayed dogs had a 3 to 7 times lower incidence of mammary tumours than the intact ones (Mulligan 1975; Priester 1979; Hahn et al. 1992; Alenza et al. 2000). The effect of spaying on the decreased incidence of mammary tumour, however, depended on the age of the dog at the time of surgery. The most significant decrease of incidence was found in females spayed prior to their first oestrus (0.5% incidence as compared to intact female dogs) and between the first and second oestrus (8%). Advanced age at the time of spaying increases the incidence of tumors (26% between the second and fourth estrus) and no positive effect of spaying was found after the fourth estrus (Misdorp 1988; Schneider et al. 1969). Characteristics such as abnormal oestrous cycle, false pregnancy, pregnancy, number of litters, number of puppies and their size were found not to represent risk factors even though some associations were confirmed (Brodey et al. 1966; Schneider et al. 1969; Schneider 1970). Because in women there ACTA VET. BRNO 2005, 74: 103-109 Address for correspondence: MVDr. Josef Zatloukal, Ph.D. Department of Diagnostic Imaging, Clinic of Dog and Cat Diseases University of Veterinary and Pharmaceutical Sciences, Brno, Czech Republic Palackého 1-3, 612 42 Brno, Czech Republic Phone: +420 602 511 428 E-mail: [email protected] http://www.vfu.cz/acta-vet/actavet.htm was higher incidence of breast tumours with fatty diet, dietetic predisposition factors were also considered in dogs. A higher incidence of mammary tumours was found in dogs receiving a “home-made” diet and “red meat” compared to commercial diets. Obesity in young animals (up to 1 years of age) is another risk factor for developing tumours even at a later age (Alenza et al. 2000; Sonnenschein et al. 1991; Alenza et al. 1998).The goal of our study was to evaluate the risk of developing canine mammary tumours in relation to age and breed. Materials and Methods Breed and age predisposition to benign and malignant mammary tumours was evaluated in dogs treated at the Department of Surgery and Orthopaedics of the Small Animal Clinic, Veterinary and Pharmaceutical University Brno between 1997 and 2001. Only patients with histological classification of specimens obtained during surgery were included into the study. Lesions of the mammary gland were classified for purposes of this study as dysplasia/hyperplasia, benign tumours and malignant tumours. When there were different lesions in one dog, the patient was classified according to the most malignant one (dysplasia benign neoplasia malignant neoplasia consider reversing the order, starting with malignant benign dysplasia). In patients treated for mammary lesions repeatedly, data obtained on the first occasion was considered for purposes of this study. All dogs referred to the Department of Surgery and Orthopaedics of the Small Animal Clinic, Veterinary and Pharmaceutical University Brno between 1997 and 2001 were included in the control group. The age predisposition to dysplasia, benign neoplasia and malignant neoplasia of the canine mammary gland was expressed as the mean and most frequent (modus) age. By comparing data with the control group we determined the relative risk (OR) of mammary gland lesions in individual age categories for each group. The breed predisposition to tumorous changes (including dysplasia/hyperplasia) and malignant neoplasia of the mammary gland was evaluated only in breeds, where the number of treated dogs amounted to at least 100 during years 1997 to 2001. For each breed we determined the relative risk (OR), which was then compared to other dog breeds using χ2 test.