Rat ttumor?

Question

privates bump   our rat private has a growth on his back left leg that is getting bigger and bigger.it's about the size of an orange now.
MY question is is it a tumor and what caused it to grow so big?
does he have to have it surgecally removed? will it keep growing? private was full grown when we got him. I have had him for 4 years so im guessing he's 5 or so. Im sendind a picture. the bump has grown bigger since the picture. Thanks

Answer
Looks like a tumor, yes. Some tumors grow very fast while others grow slow. This tumor could easily be removed, but I would never consider surgery on a rat this old. The risks are too high. Good job on taking such good care of him that he has lived so long. Four is pretty rare for a rat to live. I have only been so lucky twice out of all of the years I have had rats. Mine usually make it to be three or closer to four, which is still not the norm.  You can read more about tumors and rats on my website, sandyscrittercity.com.  Let me know after you check out my site. Here is the link to the page on tumors.

http://www.freewebs.com/crittercity/allabouttumors.htm