We know that the incidence of breast cancer in women goes up dramatically starting at around age 55, so screening with mammograms is recommended when the disease might have developed but before there are any outward signs — starting no later than age 50 and perhaps even as young as 40. It’s the same when it comes to screening men for prostate cancer. The average age of diagnosis is 66, and screening with a PSA test is recommended starting no later than age 55. Screening for other cancers, such as colon cancer, is also recommended before someone is likely to start feeling different or showing signs of the disease. Could such an approach be used for dogs so that canine cancer is caught as early as possible, with the best chance for treatment that could save an animal’s life?
A “yes” answer appears to be in sight. For instance, researchers are working on ways to screen dogs at risk for bladder cancer before they ever have clinical symptoms of the disease. It used to be that the first signs of bladder cancer were things like trouble urinating or blood in the urine. Now, scientists are working on examining urine for mutated DNA that can identify the cancer much sooner (cancer occurs when DNA undergoes an untoward mutation). Once the test is perfected, bladder cancer in breeds at high risk for the disease will be detected and treated long before the tumor has had a chance to grow and metastasize to other body tissues. Commonly affected breeds include Scottish terriers, West Highland terriers, beagles, and Shetland sheepdogs.
Liquid biopsy — examining blood for faulty DNA from a cancerous tumor — is yet another screening tool. Tumors shed their DNA into the bloodstream, so knowing the faulty DNA enables you to look for cancer and detect it reliably with a simple blood draw. It’s faster than other detection routes that involve noticing that a dog doesn’t feel or look right. It could also help take the place of always having to do a biopsy, which is invasive.
How long before various cancers are currently diagnosed should veterinarians hope to be able to identify malignant tumors so they don’t have a chance to do much damage? Researchers at a liquid biopsy company in La Jolla, California, are aiming to answer that very question.
Research looks at size, sex, and other factors
Looking at data on more than 3,400 cancer-ridden dogs who represented 122 breeds plus mixed breeds, the scientists found that the average age of cancer diagnosis in large-breed, heavier dogs such as Saint Bernards, Great Danes, and Irish wolfhounds tends to hover around the age of 6. But smaller breeds, like cocker spaniels, typically don’t get diagnosed with cancer till around age 9. Bichon frises and West Highland white terriers average about age 11.
That’s not surprising in light of the fact that large dogs age faster than smaller ones, generally speaking, and have shorter lives. But the researchers also found some other interesting statistics. Spayed and neutered dogs tend to be diagnosed with cancer a year to a year and a half later than unneutered and unspayed pets, and males in general are found to have clinical signs of cancer about a half a year sooner than females — an average of 8.3 years of age versus 8.7. When all the dogs were pooled as a single group, the average age of cancer diagnosis was 8.5. The investigators reported their findings in the journal Plos One.
Implications for
improved diagnosis
The investigators say the findings make the case that dogs in general should start being screened for cancer by the age of 7 years, even if they are not showing any signs of the disease. For dogs who tend to show signs of malignant tumors more around the age of 6 or 7, they say that cancer screening should begin as early as age 4.
As more cancer screenings become available at veterinary offices that allow for detection before a dog’s body or behavior reveals that something is wrong, more canine malignancies will be caught and treated in their very early stages, allowing our pets to lead longer, healthier lives. We will even reach a point that we are better able to screen certain breeds for cancers to which they are particularly prone, fine-tuning how to employ resources for early diagnosis. Since cancer is thought to be the biggest killer of dogs, it’s a diagnostic advance that can’t make its way into mainstream veterinary medicine
too soon.
