Cancer in Man's Best Friend

As in humans, cancer in dogs is common, but the types differ.


I remember that, once my patient was asleep, I began the operation, removing the entire rectal cancer encased in healthy surrounding tissue, the most likely approach to cure.  Then, I reconnected the two ends of the intestine, allowing my patient to once again move his bowels normally (something which for weeks he had been unable to do).

Like so many with rectal cancer, my patient had begun experiencing cramping and a change in his bowel habits, including pencil-thin stools, often coated in a thin layer of blood.

  And the cramping pain.  Pain obviously resulting from a partial blockage of the large intestine.

Yep, this was colorectal cancer.  The second leading cause of cancer death in American men and women.

But my patient was German.

And he had four legs.

Sam was a fourteen year old German Shepherd.  And Sam had rectal cancer.

Cancer is a disease of aging (although less commonly, also an affliction of children, adolescents, and young adults).  But it is a disease of aging cells, not of aging humans.  One in three Americans currently age 55 or older will be diagnosed with cancer during our lifetime, and that risk increases to one in two for those born after 1960.

In my book, Own Your Cancer: A Take-Charge Guide for the Recently Diagnosed & Those Who Love Them, I provide supportive information for those of us who love a friend or family member with cancer.  But for so many of us, our dogs are also beloved family members.

  Are our dogs prone to cancer?  Absolutely.  In fact, one out of every four of our canine companions will be diagnosed with a malignancy during their lifetime, and half of our pets age ten years or older will die of cancer.

But while the incidence of cancer is similar for both pet and pet owner, the types of cancers that dogs and humans develop share both similarities and significant differences.

  In American humans in 2015, it is estimated that there will be almost 232,000 new breast cancer cases, over 221,000 new lung cancer diagnoses, over 220,000 new prostate cancer cases, more than 132,000 new diagnoses of colorectal cancer, and almost 74,000 new cases of melanoma.  Thus the ranking of incidence of cancers in American people this years is: breast, lung, prostate, colorectum, and melanoma (this list excludes non-melanoma cancers of the skin, which are the most common and, fortunately, most often curable).

Our dogs and we share only two of the top five most common types of cancer: breast cancer and melanoma.  As with their human friends, the incidence of melanoma in canines is number five on the incidence list.  And as with human beings, malignant melanoma is a difficult malignancy to cure.  Breast cancer, the most common American human malignancy in 2015, is the fourth most common cancer in dogs.  Fortunately, as in humans, canine mammary cancer is often curable, with surgery playing the critical role in most veterinary cases.

But when it comes to the first, second, and third most common canine malignancies, our pets stray away from us, and in two cases, they stray very far.  Third in incidence in our dogs is osteosarcoma, a malignancy arising from bone tissue.  In humans, osteosarcoma is so rare that only about 800 Americans will be diagnosed with this malignancy in 2015 (half in teenagers and children).  The second most common cancer in dogs, lymphosarcoma.  Its counterpart in humans is called Non-Hodgkin lymphoma and will be the sixth most commonly diagnosed U.S. human malignancy in 2015.  And finally, the most common cancer afflicting our dogs is hemangiosarcoma.  Forming in the blood vessels (often in the spleen), this number one most common canine cancer is so rare in humans that less than 200 cases will be diagnosed within the U.S. human population this year.

Given that several common canine malignancies are rare in humans, what should we as pet owners be looking for?  As in the case of many humans, cancer in dogs presents as abnormal weight loss, a new lump, fatigue and lethargy, a new cough, vomiting or diarrhea, weakness, or pain.

We love our dogs (my two rescue canines, Dot and Sugar, as lying on the floor next to me as I pen this article).  While the types of cancers that our beloved dogs develop often differ from those that afflict us, it is critical as loving dog owners, we recognize that our pets also share a significant risk of cancer development, and we should always be on the lookout, particularly as our friends get older, for signs and symptoms similar to those that worry us in ourselves and our human loved ones.  After all, they are part of our family.

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