Cancer in Dogs Part I: The Importance of Early Detection
Most veterinarians will agree that cancer is a significant concern for canine patients. Although both dogs and humans have roughly a 1-in-3 risk of developing the disease, dogs have much shorter lifespans, so the annual incidence rate in dogs is actually 10 times higher than in humans.
Approximately 6 million new canine cancer diagnoses are made each year in the United States. Unfortunately, the disease is not only common but also deadly. It is the leading cause of mortality in adult dogs, taking more furry best friends than the next five causes of death combined. Why is this disease so challenging to combat, and how can cancer screening provide better early detection?
How DNA Changes Cause Cancer
Put simply, mutations in the DNA of cells can cause cancer. If the abnormal cells have an advantage over neighboring healthy cells, they replicate faster and survive longer. Eventually, they could form a tumor. The cells that make up the tumor continue to develop new mutations to dominate the healthy cells. By the time a tumor is detectable by physical exam or imaging—usually, when it's about the size of a pea—it typically harbors various populations of abnormal cells, each with its own unique set of mutations.
These unique mutations are a problem. When attempting to treat tumors with methods such as chemotherapy, many cells may respond and be eliminated, resulting in clinical remission; however, some of these cells may have mutations that make them resistant to treatment, allowing them to remain at clinically undetectable levels and fly under the radar. Then, when treatment has eliminated the bulk of the tumor cells, these insidious, resistant cells are able to expand in the absence of competition, resulting in recurrence of the disease.
Why Early Detection and Treatment Is Critical
So, how can veterinarians defeat such a tricky opponent? Success is most likely when they can detect and treat cancer as early as possible. Human medicine has demonstrated that cancer develops over time and that early detection is the key to improved outcomes. This is why mammograms, colonoscopies, and other screening tests are recommended for adults at set intervals starting at specific ages.
Several veterinary medical organizations recognize the importance of early cancer detection in dogs. However, guideline-driven screening protocols for early detection are lacking. The current standard of care for cancer screening in dogs is the annual or semi-annual physical examination and wellness visit. Although these examinations are important for the health of aging patients, they are not enough to confidently detect preclinical cancer. Unfortunately, it's not until most dogs show clinical signs that cancers are identified—and by then, it's often at an advanced stage, and long-term control or cure is unlikely.
Once cancer is detected in a dog, a wide range of treatment options exist to help combat the disease. Just like in humans, surgery, chemotherapy, radiation therapy, and immunotherapy are all available tools, and are generally well-tolerated by patients. Some newer therapies even allow for treatment at the general practitioner's office.
What Early Detection Means
Novel technologies may be opening the door to early cancer detection in dogs, but what does "early" mean and how can it benefit patients?
Early detection can be defined in two ways: detection at an early stage of the disease (early-stage detection) or detection prior to the onset of clinical signs (preclinical detection). Early-stage detection leads to better outcomes for a variety of cancer types, such as lymphoma and hemangiosarcoma, among others.
Dogs who have cancer but have not yet developed clinical signs tend to demonstrate improved outcomes, including patients with lymphoma, brain tumors, and mast cell tumors. Also, since these dogs do not need to be treated for clinical signs or stabilized prior to starting treatment, they are often easier to manage which may result in less emotional and financial burden for their owners. In short, early detection, whether it be early-stage detection or preclinical detection, has far-reaching benefits for dogs, their families, and their medical teams.
Features of an Ideal Screening Test
So, what would an ideal cancer screening test look like? It should:
- Be non-invasive and allow for convenient repeat testing at regular intervals
- Increase the opportunity for early cancer detection
- Have the ability to identify a variety of cancer types
The last point is particularly important, as an ideal screening test would detect disease anywhere in the body, at any stage. At the very least, it should put cancer on the radar when perhaps it's not generally.
The Power of Genomics
Stay tuned for the next article in this series on canine cancer introducing liquid biopsy, a novel technology that leverages the power of genomics to detect cancer in dogs from a simple blood draw. This new test allows veterinarians to finally say "yes" when asked, "Is there a blood test to detect cancer?"