Survey of Animal Neoplasms in Alameda and Contra Costa Counties, California. II. Cancer Morbidity in Dogs and Cats From Alameda County2

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Abstract
The malignant neoplasm cases reported from Alameda County, California, during 3 years, to a central animal neoplasm registry, were analyzed to provide estimates of cancer incidence in dogs and cats, and to measure the effects of age, sex, and breed on cancer development in these species. The estimated annual incidence rates for cancer of all sites were 381.2 per 100,000 dogs and 155.8 per 100,000 cats. The annual incidence rate for all cancer in Alameda County human residents was exceeded by the comparable canine rate, and both canine and human rates were over twice the feline rate. The Mantel-Haenszel procedure was used for testing possible associations between sex and breed characteristics and cancer of specific sites. Male dogs had greater relative risk of developing cancer of the mouth and pharynx than female dogs. Male cats had greater risk of lymphosarcoma than females. Neutering had a significant sparing effect on mammary cancer development; both intact female dogs and cats had approximately sevenfold greater risk of developing mammary cancer than neutered of the same species. Purebred dogs were significantly over-represented among cases of cutaneous malignant melanoma and mammary cancer. The boxer breed had a significantly higher risk than other purebred dogs of developing malignant melanoma of the skin, other skin malignancies, and cancer of connective tissue. German shepherd dogs had a greater risk of developing oral and pharyngeal cancer. Chihuahua dogs and Siamese cats were significantly underrepresented among skin cancer cases (melanomas excluded). Animal cancer models for studying breast cancer in women, genetic effects upon carcinogenesis, and human leukemia are discussed. Future studies of animal cancer should provide comparable morbidity information in other areas to permit identification of geographic differences and clues to the etiology of neoplasia.