I'm so sorry to hear that your little boy's cancer metastasized to his chest.
If your not seeing an oncologist already then i would ask your vet to refer you to one. If you are already seeing an oncologist as well as your regular vet then i guess you can always try a holistic vet or acupuncture. they're worth a shot, and you've got nothing to lose.
Its so sad to see such a young dog who is so full of life get cancer like that. The best thing you can do for him and yourself is to make every day count. enjoy your time together and have as much fun as you can.