Thank you for your patience. Good on you for wanting to do all you can to give your boy a good quality of life. I am sure your vet will have arranged some appropriate pain medication, potentially an anti inflammatory and an anti nausea drug for you to use as needed with your boy. If not, definitely discuss this with them.
There are a few very good supplements on the market, as well as an excellent diet. It sounds like you understand completely that this will just help to give your boy some strength and help to maintain his muscle mass as his cancer develops further. Unfortunately there are no magic treatments for SCC in dogs as yet - hopefully one day soon. Firstly, I will direct you to site that has products that would be beneficial for your boy. These include a range of vitamins and minerals as well as high levels of omega 3 fatty acids: http://www.dogcancer.net/pet-products/dog-immunity-supplements/dog-cancer-support-trio/ . You should also consider this interesting new supplement for this type of situation as well: http://www.1800petmeds.com/Apocaps+CX-prod11651.html?q=cancer+supplement
As far as nutrition goes, you really can't go past Hill's n/d for this situation. You can read more about this online here: http://www.hillspet.com/products/pd-canine-nd-canine-canned.html . This diet has high levels of protein to help prevent muscle loss, as well as high levels of certain amino acids, and omega 3 fatty acids for their anti inflammatory effects. This would be an expensive option for your boy however, so you could continue to feed his regular food and supplement with a fish oil supplement like this: http://www.1800petmeds.com/Nordic+Naturals+Omega+3+Pet-prod10859.html
Ultimately - the goals here for your boy are to ensure he keeps his muscle on, to minimize inflammation and ensure he is getting a boost in vitamins and minerals. He also needs to be on a high calorie and palatable diet, since as this disease progresses, he is going to find it harder to eat, so smaller, higher calorie meals will be best.
I hope all of the above makes sense? If you have more questions or if I can help in any other way, please do not hesitate to ask! If you would like to accept my answer, please press RATE OUR CONVERSATION (I am not compensated in any other way). Bonuses are always welcome. Thanks! I hope to work with you again soon!
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