lump in dogs chest

Question
I have a 10 year old golden retriever/collie mix with  a golf ball sized lump on his chest. He is in excellent health, eats well,plays, doesn't seem to be in any pain. However, on occasion, he gags and throws up yellowish looking fluids. Do you think this is cancer? Also, is it possible that he is in pain and not showing it?
Thanks for your advice.

Answer
You can have your veterinarian do a fine needle aspirate of the lump in the office to determine what it is.  You may also want to consider having some blood tests run as well as a chest and abdominal x-ray since he is older.

The gagging and vomiting could be related to a sensitive stomach or over production of acid...for that I would recommend adding digestive enzymes (Dancing Paws Shake 'N Zyme is an excellent product www.dancingpaws.com ) to his food on a daily basis.  And make sure to feed a high quality, all-natural diet that is free of dyes, preservatives, corn and by-products.  Also, feeding 2 or 3 meals a day would help versus one big meal.   

Dogs can be uncomfortable and in some degree of pain and not show it due to their survival instinct.