Last updated on Thursday, 14 October, 2010 17:48
What is a fibrosarcoma?
A type of cancer that afflicts humans, but also cats and dogs.
Let's start at the beginning. In the beginning there was.... O.K. Maybe not so far back. I'll start by explaining what kind of cell it was supposed to be and then what a fibrosarcoma is in relation to that cell.
Any animal more complex than a jellyfish has three main types of cells in its body. You see, after the embryo of an animal is formed and starts to grow, the mass of cells differentiate into three different categories. One becomes the endoderm (inner layer), which later gives origin to the GI tract, lungs, the bladder, and a few other things. Another becomes the mesoderm (middle layer), and that will be where your muscles, bones, heart and major vessels, cartilage, and a bunch of other stuff comes from. The other cells will then transform into the ectoderm (outer layer), which is mostly responsible for your nervous system and epidermis (skin). It may not seem that they're closely related, but this is why melanomas - skin cancers - metastasize to the brain. In general, tumors spread to areas of the body that share their cellular origin.
The type that is relevant here is the mesodermal origin. In the embryo, the mesenchyme (basically, what's inside the embryo) gives birth to many specialized cell types, but in particular, to cells called fibroblasts. These are very important as they are responsible for the extracellular matrix, the so called stroma, which is basically the glue that holds your cells in place (this makes fibroblasts the most common cells of the connective tissue).
What do they do most of the time, you ask? They are the cells that allow your body to grow, and specially, to heal wounds. Whenever you have a cut, those things are responsible for the closing of the wound, amongst other things. Tissue damage awakes them from their dormant state and makes them multiply.
Sometimes, the cells malfunction. It may be caused by a virus, radiation, whatever. This can cause normal cells to mutate into something else, which may lead to what is usually called a metaplasia (given that a considerable number of cells mutate). Moreover, those mutations don't always cause functional changes. Sometimes, the cells start presenting abnormalities, causing them to multiply more that planned, in what can become a dysplasia (not a cancer yet). Now, the body's immune system has some ways of keeping these cells in check, preventing them from multiplying and sometimes it is even capable of returning them to normal. But sometimes, normally due to the influence of some unusual external factor, it is not able to fix these problems and then the cells can go crazy, multiplying when they shouldn't and going where they're not needed. After a while, they are just to damaged to be controlled. And here is where things go wrong.
A fibrosarcoma is born.
There are several degrees of malignancy to a fibrosarcoma, which relate simply to how much do the cancer cells look like the original fibroblasts. A low-grade fibrosarcoma is when the cells still retain their overall shape and still do what they're expected to, not multiplying all that much, just having gone rogue. A high-grade fibrosarcoma is when the cells look atypical (it gets really weird), they multiply a lot (though sometimes with errors), and have lost most of their functionality.
A fibrosarcoma is a rare tumor in humans, but it happens to cats and dogs with worrying frequency. There are some suspicions as to why this is, but I'll go over that in the next chapter.
This kind of tumor also doesn't tend to metastasize all over, though it sometimes happens, specially with more specific tumor lineages (hemangiosarcomas, osteosarcomas, etc...), and their mitotic rate doesn't usually cause them to compete too heavily for resources with the other cells around them. But they do grow uncontrollably and those masses end up causing serious problems. Think of them as huge balls of scar tissue. They serve no purpose and they can still suck up precious resources.
Anything of this kind will also cause a whole host of other problems (ever seen a episode of House, M.D.?), like paraneoplastic syndrome, but for me, the worst part is the necrosis the fast growing cells experience. After a while, they outgrow their blood supply and start to die out. Seems good, right? Wrong. More of them keep coming, but when these cancer cells die, they burst open and release their contents into the blood stream. It's the same stuff you would find in most cells, but certain things in excess, like potassium, are potentially lethal. They will also overload the kidneys as these struggle to process all the excess salts and urea introduced to the organism.
This particular tumor has slightly different presentations in cats and dogs, compared to humans. In humans, outside of juvenile tumors, it mainly appears in males with ages between 30 and 40 years, and locates itself mostly in the bones. In dogs, it is more commonly seen it the mouth (gums, mostly) while in cats it can come up all over the body, but unfortunately, they tend to appear frequently in between the shoulder blades, in the scruff (frequent vaccination site), where removal is troublesome.
It isn't weird that cats and dogs both get this because their two species are as closely related to each other as humans are to orangoutans. It also seems that their predatory evolution makes them more susceptible to this illness, as I'll explain in the next section. There is also some info that indicates that their relationship with humans isn't helping them here either.
If you have been left curious for more or wondering about this subject, you can always start in Wikipedia, and move your way up to medical articles on this subject. I will leave some good links on this subject here, but I also recommend reading The Body Electric as it will help you bring the data into a broader context about cell function and life. You don't have to take the claims in the book as absolute truth, but rather, you can use the explanations to make sense of what a fibrosarcoma really is.
Here are the links: