Osteocarcinoma

[Tommy Coyote]

I just found out that one of the dogs I have taken care of for a long time has this bone cancer. I thought we were going to lose him 2 years ago when he became paralyzed in the rear end. But he got better and was able to walk pretty well. He walked very stiff legged and sometimes he would be in a lot of pain. But the pain meds controlled it really well.

 

I was reading up on this and then I realized it's very possible that this is what killed another favorite dog, a golden, a few months ago. He was having trouble swallowing and his bark had gotten hoarse. He was also having trouble placing his feet. He was gone a week later when he started seizing and died.

 

And there was another dog a couple of year's ago that the vet - without an X-ray - said was just arthritis. But that dog was in awful pain and died not a week later.

 

How common is this stuff? Or have I just been really unlucky.

[Liz P]

Not unusual in larger breed dogs. It's not a nice cancer to get since it tends to be pretty aggressive and already spread by the time it's diagnosed.

[Gideon's girl]

I've had 2 get it. Both about 20 years ago. Both got it in the left rear leg. One day they were fine, the next they were 3 legged, and less than a week later we put them down. Maybe it was osteosarcoma instead, but still nasty bone cancer.

 

I remember us doing surgery on a greyhound and the vet all of a sudden swore. He had been taping a spot that looked queer, while he thought about what it reminded him of, when his scalpel just went right in like a knife through butter.

[Pearse]

I did my graduate work on osteosarcoma starting in dogs and later in humans.

 

The incidence goes up exponentially with size. Small dogs rarely get it, it's common in giant breeds. I have some hypotheses why but never did get the chance to follow up on that research. Basically, I think that what makes big dogs big is a potent growth promoter for osteosarcoma. There are probably other breed-associated contributing factors (possibly genetic).

 

The same pattern is true in humans. It's most commonly seen in adolescent males of taller than average height. Better prognosis in humans because it's usually diagnosed earlier. One of the more famous human patients was Canadian Terry Fox who was diagnosed in 1977 and in 1980 started a cross-country run across Canada to raise awareness. He was forced to stop in Thunder Bay ON when he discovered the cancer had spread to his lungs and died in 1981.

 

Liz is correct. Usually by the time it is diagnosed in a dog, it has metastasized. Amputation can give local pain relief but with no other treatment, life expectancy post-surgery is 3-9 months.

 

There are a few centers (Colorado State is one, U of WI is another) that were doing limb-sparing surgery using treated bone allografts as scaffolding for new bone growth (often impregnated with chemo drugs) in combination with various chemotherapy regimens and they have had some success. I'm not up to date on the most current literature.

 

The project I was working on used monoclonal antibodies directed against a tumor-specific antigen attached to either radionuclides or a pokeweed-derived toxin to kill cells. It showed promise in cell culture and mouse studies but technical difficulties and toxicity issues made its use in humans or dogs impractical.

 

Pearse

[Liz P]

Pearse, did you explore the idea that chronic damage and inflammation is a trigger? IOW, large breed dogs and dogs that run/work hard are at increased risk. We do know that sites of previous injuries, especially plates, pins and screws, are at risk of developing osteosarcoma.

[Tommy Coyote]

Do you have any stats on how common this cancer is in bigger dogs?

 

I did read that it either hits young dogs - 1 or 2 years old - or older dogs - 7 or 8 or older. I think Pam had a 1 year old lab she was working get this stuff. That would be so awful.

[Pearse]

Pearse, did you explore the idea that chronic damage and inflammation is a trigger? IOW, large breed dogs and dogs that run/work hard are at increased risk. We do know that sites of previous injuries, especially plates, pins and screws, are at risk of developing osteosarcoma.

 

Liz,

 

I didn't look at that specifically and there was nothing in the literature that suggested it was a specific contributing factor. However, I would speculate and say that almost all of the dogs in the various epidemiological studies were likely pet dogs not working dogs.

 

That said, I would (again speculation) say that it is extremely likely that any chronic inflammatory condition will result in conditions favorable to cancer cells. This seems to be an emerging common theme in many kinds of cancer. The inflammatory cytokines (chemicals produced by cells in response to injury which signal other cells to come to the site and deal with dead and dying cells or foreign material/organisms) are frequently cancer promoters.

 

It's unlikely that inflammation causes osteosarcoma per se, but once the cells are there it could help them survive.

 

Like I said, in humans we see this disease a lot in teenaged athletes, but whether athletics is a contributing factor, or whether it's just that basketball players tend to be taller, early developing, teenaged boys and taller, early developing teenaged boys are at greatest risk is not clear.

 

The other thing is that growth plates at the end of long bones, and the sites of screws, plates, etc are sites of bone remodeling activity. Osteoblasts and osteoclasts are actively dividing there so those cells are more likely to accrue DNA damage, plus all of the growth promoters are present at those active remodelling sites, and those growth promoters help cancer cells survive.

 

One interesting thing is what makes big dogs (and humans) big. The levels of growth hormone in small dogs and large dogs is roughly the same. The levels of IGF-1 (insulin-like growth factor) scale almost linearly with size. IGF-1 (or its receptor) has been implicated as a cancer promoter, and is being looked at for its role in aging (*total wild speculation* which may explain why large dogs don't live as long). It's certainly not a simple relationship and it's probably not something we can do much about.

 

Pearse

[Pearse]

Do you have any stats on how common this cancer is in bigger dogs?

 

I did read that it either hits young dogs - 1 or 2 years old - or older dogs - 7 or 8 or older. I think Pam had a 1 year old lab she was working get this stuff. That would be so awful.

 

there is a small blip in incidence in young dogs but most are 7-8 years old (it probably takes that long to accumulate the mutations necessary to go from normal cell to cancer cell, the young dogs are likely born with one or more mutations already - not necessarily inherited but possibly).

 

There's a really good, up to date summary at Mike Modiano's lab page at the University of Minnesota for anyone who is interested.

 

http://www.modianolab.org/cancer/cancer_osteosarcoma.shtml

[Liz P]

The youngest animal I have personally diagnosed cancer in was in a 9 month old Labrador. I have read a case study of a 3 week old pup with leukemia. As a vet student I had a case of a 10 month old Morgan horse with hemangiosarcoma. Cancer in your animals (and kids) is particularly depressing.

[Tommy Coyote]

Thanks for the info. I will pass along to these owners. It's such a horrible thing to go through. I think that understanding is helpful.

 

What do they mean by food that promotes too fast growth? Too high in protein? Too high in calcium

[Gideon's girl]

Usually that means too high calcium or too many calorie fed to the dog, no matter the food.

[Tommy Coyote]

Don't they have special foods now for those big, fast growing dogs?

 

Two of these dogs I mentioned were shepherd mixes. The other one was a golden. The shepherd mixes neither one had a very good diet. One was on Beneful and the other was a grocery store premium brand. Both are mostly corn, I think. The golden always was on a better food because he had stomach issues. They were all right around 12.

[Gideon's girl]

Most of the large breed puppy foods are still too high in calcium according to the current research. A lot of the formulas focus on old faulty studies that said too much protein was the issue. That has been disproven for quite a number of years, like 15 or so, but the foods have still not caught up with current research.

[Pearse]

Thanks for the info. I will pass along to these owners. It's such a horrible thing to go through. I think that understanding is helpful.

 

What do they mean by food that promotes too fast growth? Too high in protein? Too high in calcium

 

too high in protein. It's been shown than diets lower in protein lower IGF-1 levels, slow growth, and reduce cancer incidence (in lab animals).

 

Rats and mice fed a low protein, calorie restricted diet, lived much longer lives. There's some epidemiological data to show the same is true in humans.

[Maralynn]

What is the definition "low protein" in this context? And then how would a low protein diet work for an animal like a working dog?

[Tommy Coyote]

Don't they sometimes feed low protein diets to guard dogs to keep their energy level lower so they don't get too rambunctious and kill the lambs? Or is that something I heard 30 years ago and no one does it anymore?