Scientists at the Purdue University School of Veterinary Medicine, in Indiana, have discovered that benign mammary intraepithelial lesions, which can lead to breast cancer, are similar in dogs and humans
New research shows that pre-malignant breast cancer cells in dogs are similar to those in humans. 
Photo: Jonathan Davies
This could lead to the development of new treatments and a better understanding of how the disease progresses.
Scientists at the Purdue University School of Veterinary Medicine, in Indiana, have discovered that benign mammary intraepithelial lesions, which can lead to breast cancer, are similar in dogs and humans.
"Dogs develop these lesions spontaneously in contrast to other available models and are exposed to the same environmental risk factors as humans," said Professor Sulma Mohammed, an associate professor of comparative pathobiology.
However, there are no models yet for diagnosing these lesions in animals. Professor Mohammed says that dogs would be an ideal model to compare the breast lesions, and could help in the development of customized treatment and prevention strategies. If a lesion is estrogen-receptor (ER) positive, it can be treated with hormonal therapy. But, for low-risk and ER-negative lesions, no treatments are currently available.
Professor Mohammed suggested that a dog model would allow researchers to study these lesions and test different preventative methods before they became cancerous. Dogs provided a more realistic comparison to humans than mice and rat models, because the tumors in dogs and humans developed spontaneously, she added.
In a study of precancerous lesions in tissue surrounding tumors of 212 biopsies taken from 200 female dogs, researchers found that the lesions were "strikingly similar" to those diagnosed in the human breast.
"We found that preneoplasia lesions are virtually identical, microscopically, in dogs and women," said Dr Mohammed. "In fact, many of the slides were so similar that it was often difficult to determine if they were from dogs or people without looking at the label."
Dr Mohammed says that much of the previous research conducted on dogs with breast cancer is outdated. However, breast cancer has become one of the most common forms of canine cancer now studied at Purdue's Animal Disease Diagnostic Laboratory, says veterinary pathologist Dr Margaret Miller.
Dr Mohammed plans to determine the frequency of the lesions in dogs that do not have tumors. Both she and Dr Miller hope to use a noninvasive screening method such as magnetic resonance imaging or ultrasound to find the lesions. They are also looking at breast cancer in cats, which they say has a malignancy rate of 90% when diagnosed.
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