Occurrence of Spontaneous Mammary Intraepithelial Neoplasia in the Canine Mammary Glands and Estrogen Receptor Reactivity

Abstract

Cancer is one of the leading causes of death in both man and dog. Dogs, however, develop tumors approximately twice as frequently as their human counterparts. Studies have found that 45% of dogs that live to be 10 years or older die of cancer (Hahn et al., 1994). Mammary cancer is the most common neoplasm in the female dog, representing 52% of all neoplasms (E. G. Macewen, 1990). Benjamin, Lee, and Saunders found that 70.8% of the female beagles had at least one mammary neoplasm; two males were also found to have them. This study also found a significant association among related animals in the estimation of possible carcinoma. Some families were also predisposed to an early onset of cancer (1999). Prevalence also varies by breed, with the Chihuahua having the lowest incidence (Benjamin, Lee, and Saunders, 1999). Some breeds have shown to have increased risk of breast cancer; these include the smaller types of poodles, several types of spaniels, German Shepherds, Yorkshire Terriers, and Dachshunds (Sorenmo, 2003). Dogs are useful in cancer prevention studies. While the study is done in canines, it may also be applied to fight human breast cancer. Other non-human mammals are often used, full clinical tumors are studied in mice using human cancer cells which can be injected and then grown. But for studying cancer development and progression, spontaneous cancer in dogs is a better model than the induced cancers in other laboratory animals. Prostate, bladder, and bone cancer in canines are very similar to their human counterparts (Knapp and Waters, 1997). Because pets are exposed to the same environmental factors, their cancers develop in much more similar pattern to humans. Dogs also have metabolism that better match that of humans, in contrast to laboratory rodents, making preliminary drug tests more meaningful (Knapp and Waters, 1997).