No Blame In Cancer

Here's a question from Stefanie...

I just recently found out that my 14 year old Queensland Heeler/Australian Shepherd dog has a squamous cell carcinoma in her throat. It is attached to her soft palate and left tonsil and is quite large. (I was shown a picture of it) To quote the biopsy results "poorly differentiated, aggressive, locally invasive". Since she is 14 - after discussing options with the vet (her recommendations were referral to an oncologist, "debulking" the tumor which would buy some time but not necessarily prevent it from growing back, or just keeping her happy and comfortable for as long as possible). I was told she has 3-6 months and the tumor will likely eventually cut off her airway. I chose option three - keeping her happy and comfortable and will put her down when the gasping for air and choking become much worse than what they are now.
 
My question is - did I do something that potentially caused this cancerous tumor in her throat? I have to tell you - she has always enjoyed chewing/eating stuffed animal parts, sticks, other debris in the yard and anything she can get a hold of in the house if I am not paying attention. Because of this - in order to help her pass these items - for the past several years - I have given her petroleum jelly (less than a tsp) once a day. My concern was always to prevent intestinal blockage - so I never even considered the possibility that it may cause her harm.
 
Any light you can shed on this would be appreciated. I love this dog dearly - she has been my constant companion since she was 10 weeks old and I hate the thought that I may have caused her harm, but on the other hand - would like to be educated so that I do not repeat the same mistake for any future dogs I may care for.

First I have to say that I'm very sorry for her medical problems.  This type of cancer usually is very aggressive and this is a difficult location to have it.  I would agree that the best thing to do at this point is to make her as comfortable as possible and enjoy the time you have left.

Let me set your mind at ease that you didn't cause this.  We don't have good data in pets regarding environmental factors leading to cancer, unlike human medicine where there are numerous factors identified that can increase or decrease cancer risks.  There are some things that can increase risks in pets, such as feline leukemia, subcutaneous injections or punctures, and certain toxins or radiation (as in humans).  But most of the time cancer is due to genetic and physiological factors that we have no control over.

In a nutshell, a tumor is a particular type of cell that grows uncontrollably.  Each cell in the body has mechanisms that tell it to stop reproducing or lead to the cell's death if there is damage.  Much of this protection is at the level of DNA, though there are external factors such as immune cells that seek out and destroy cancerous cells.  In order for a tumor to develop, all of these defenses must fail.  Truthfully, it's a wonder of nature that we don't see much more widespread cancer.  But you should be aware that in most cases of cancer in pets there is no single, preventable cause.  This means that for better or for worse, you couldn't have prevented this from happening to your dog.

To also specifically address your concern, I've never seen any link between petroleum jelly and cancer in dogs.  Also, in a dog this size a teaspoon or less probably didn't significantly help with lubrication.  But even if it didn't help, I can't think of any reason why it caused any harm.

Fourteen years is a great life span for any dog.  I lost my own dog to cancer a few months ago and she was only five.  I can certainly understand what you're going through.  It's not easy to go through this, but know that you have given her a great and long life.  Enjoy the time left with no regrets.