Can Previous Injuries Cause Bone Cancer in Dogs?
When it comes to serious conditions such as cancer, risk factors need to be considered and a history of previous bone injuries may appear to be a risk factor, but there seems to be conflicting information on this. First and foremost, what exactly are risk factors? A risk factor is something that predisposes an animal or person to develop a certain disease. So in the case of skin cancer, we know that sun exposure is a risk factor; whereas, when we consider lung cancer, we know that cigarette smoking is a big risk factor. There have been claims that past injuries may be a risk factor for bone cancer in animals and people, but how true is this?
First off, it's important to clarify that a risk factor should not be confused with a guarantee. In other words, a risk factor doesn't necessarily mean that a certain person will get the disease. When it comes to diseases, there are many other factors involved which explains why your uncle Bob may have never gotten cancer despite smoking like a chimney and eating junk all his life, while aunt Sarah developed cancer despite leading a healthy lifestyle with loads of great food and exercise. As in people, when it comes to cancer in dogs, one must consider several factors such as diet, the immune system, genes, age, the environment, and much more. Many times, the actual culprits cannot even be found. So a risk factor or even several of them don't necessarily create disease, unless there are other contributing factors at play. But we may never be aware of them because it takes quite some time for cancer to develop.
Do Previous Injuries Contribute to Bone Cancer in Dogs?
As mentioned, there seems to be conflicting information on this and we need to see several sides of the story to better understand the dynamics. There are several websites claiming that, yes, previous injuries may lead to bone cancer, but then some considerations aren't taken into account. For instance, according to the Merck Manual Pet Health Edition, veterinarians and researchers seem to agree that physical injuries such as the average short-lived bumps and bruises aren't considered risk factors for cancer. However, there is speculation that areas of chronic inflammation, as found in past traumatic injuries, may be more susceptible to the development of sarcomas years after the injury occurred. The National Canine Cancer Foundation seems to agree, claiming that anomalies in the bone such as areas of healed fractures can sometimes leads to osteosarcoma
Interestingly, the American Cancer Society has a slightly different theory. The website claims that whether an injury to a bone is a risk factor for cancer is something that has yet not been proven, but it may seem that way if we consider that the injury drew the patient's attention to that bone. The patient may have the area examined only to discover he has bone cancer. Therefore, he may think that the injury is what caused the cancer to develop. Cancer Research UK seems to agree that there are no research studies to support the correlation between previous injuries and cancer. Their belief is that, more likely, an injury may cause swelling, which then turns out being a sign of cancer that is already there, or in another case, a bone becomes weakened because of cancer and is therefore damaged in an accident and then the doctor spots the tumor making the patient believe it was the accident that caused the tumor in the first place when the opposite is true.
The same may happen to dogs. If your dog for instance injured his leg years ago and then you decided to have the leg re-checked, and the vet found cancer, you may think that the injury caused the cancer in the fist place when the two factors may not be correlated, or at least, we don't have proof of that possibility yet. In another case, your dog may have pain and swelling after playing in the yard, and then one day since the problem persists, you decide to have the area checked out convinced that your dog was injured only to find out your dog has cancer. You may therefore think your dog's cancer took place because of the injury, when in reality it was cancer that actually caused the injury.
About Metal Implants Causing Osteosarcoma in Dogs
There's belief that a previous injury may indirectlybe linked to cancer. This is the case where a dog was treated for a previous injury such as a fracture or a torn ligament requiring the use of implants to the bone such as pins, screws or metal plates. According to Merck Manual, these sites of implants have shown to be a risk factor for sarcomas compared to other parts of the body. On top of that, one must consider that cutting the bone and placing screws into it are also forms of trauma.
In regards to this, actual studies have been conducted. In 2005, the Journal of the American Veterinary Medical Association discussed the case of a German Shepherd Dog that developed osteosarcoma after undergoing TPLO. It was found that the implant corroded. This case can be found in JAVMA, November 15, 2005, Vol. 227, No. 10 “Sarcoma of the proximal portion of the tibia in a dog 5.5 years after tibial plateau leveling osteotomy,”
A study conducted between 1999- 2009. Sartor A, Selmic LE, Withrow SJ, Ryan S evaluated 437 dogs undergoing TPLO. Thirteen dogs developed osteosarcoma; out of these, 6 developed right at the TPLO site. Over 12 years, 1 out 100 dogs developed osteosarcome on TPLO site. Dogs with bilateral TPLO affecting both legs were 8.4 times more likely to develop TPLO-site bone cancer than dogs with unilateral procedures. Overall, the incidence was overall low and the belief is that the inferior quality of the metal used back then contributing to wear which stimulated the development of neoplastic cells. Problematic were the non-medical grade metals (Slocum Implants). Nowadays, care is used in utilizing higher quality metals less likely to corrode.
As seen, the subject of "does a previous injury predispose to bone cancer in dogs?" remains a subject of controversy. Perhaps it's because there is no proof yet and more studies need to be be done. What does it mean to the dog owner? It means that it doesn't hurt for owners of dogs with previous injuries and with surgical hardware implanted in their bones to play it safe and keep a watchful eye for signs of bone cancer in dogs.
Disclaimer; this article is the result of my own research on this topic and should not be used as a substitute for professional veterinary advice. If your dog has a health problem, please consult with your veterinarian.