Welcome to Gaia! ::

I have a rat and she will be 2 years this december. About a 2 monthes ago i fould a large lump under he left arm. I had no idea what is was, a let some time go by and it seemed to get smaller. Then one day it was huge, i am starting to get worried because now she is getting lighter. She is always sneezing also. Can anyone give some adivice please.

wow this post was made a long time ago,,/

But for the record it might have been a sist..or however you spell it.

But yes.. Rats can get cancer.
especially if you have a male and you feed him orange juice, apparently theres a chemical thing that happens.
Anyways.... if your rat is 2, its possible that she is developing problems due to old age. Rats are suppose to live to be 1 year... 3 if your really lucky. So your rat sounds like its time might be coming to an end. I was extremely lucky and had my rat live to be almost 5... but really, sometimes its better to not have your pet last to be ancient. .. its hard when you start seeing them get weaker and weaker and they just keep hanging in there regardless.
As for the sneezing, rats are known to have respiratory problems, especially in relation to the type of bedding you use. PINE is NOT GOOD for RATS. It's extremely dusty for them, even more dusty if they're in an aquarium where you dont have proper air flow.

Sorry this is so late, You probably dont have your rat anymore, but maybe others will read this.