Swollen gland or growth

Question
We have two female Guinea pigs. One is three years old and the other is a year and a half. For the most part they get along really good,but over the last six months they start getting edgy towards the last week of the month. We just assumed it was that time of the month and it normally stopped. But over the last three months the younger one was getting some cuddle time and during that we noticed a dime sized bump on her lower left mammory gland. We kept an eye on it and it stayed the same size. This last month it has grown to about a half inch wide and two inches long. And when you touch it she doesn't show any pain or even act like it bothers her. But she seems to be aggressive and agitated more. Everything else is fine with both of them eating moving and drinking all good. The question I have is could this just be a gland that is swollen and will go away or possible cancer? Any ideas would be great.

Answer

Malignant tumor   Diagnosing a lump based on a description is difficult at best, and I am sure you're hoping I can give you a handful of hope in my answer.

Although not terribly common, mammary tumors do occur in sows. The majority are malignant.

The most concerning thing is the size and the sudden rapid growth. The fact that is causes no discomfort or pain when palpated which would seem to indicate this is indeed a form of mammary cancer. Abscesses are typically soft and pliable, somewhat moveable and are filled with fluid. A malignant tumor is attached to the tissues and cannot be easily moved. There is not pain within the tumor itself. Pain is caused by the damage done to muscles and tissues to which it has attached and spread.

Most female pigs are between the age of four and five when they develop these cancers, however cancer is not known to always follow the rules. So it cannot be excluded simply based on age.
I have attached a picture sent to me a few years ago on this site of a sow with what the owner had hoped to be just an abscess. She took it to her vet after writing to me, and it was indeed a malignant tumor, advanced to the point of opening up.

It's always difficult to have to make a decision between budget and heart. I would recommend you get your vet's opinion as to what he or she thinks it could be. He may suggest a needle biopsy, which aspirates some of the tissue to be examined under a microscope. If there are malignant cells they should be visible.

The vet may also share my concern that this tumor is oddly shaped or poorly differentiated, giving even stronger suggestion that this could have already metastasized and spread to other parts of the body.

Treatment on a small animal is not inexpensive, and the treatment for cancer is not less costly for a guinea pig than it is for a dog or cat. If you know what you are dealing with you can more comfortably make a decision as to how far or not to go with treatment.

I know there are many pet owners who believe that all efforts should be made to save a small pet regardless of cost.  I personally have a more pragmatic view and feel that there is no shame in making a decision based on what your finances will allow. With cancer you are always faced with the possibility that you will not be successful. You must decide how much you would put that pet through with the treatment, and is it really the best option for the animal?

These are hard decisions to make and there is no right or wrong answer. There is also no shame in being realistic. I would support whatever decision you have to make.  

I realize I am not giving you an optimistic opinion, and for that I apologize. Your vet would best able to give you a real working diagnosis as to what this is and what may or may not be done.  Whatever your decision, my heart goes out to you and I hope you will keep me posted as to the outcome.