First, my sympathies for your Baylie's diagnosis. Canine cancer is sadly more common than one might expect, with 1 in 3 dogs developing cancer at some point in their life. I've lost 3 shelties to different forms of cancer since 2012, the most recent being my 7 year old rescue, Copper, who was diagnosed with T-Cell lymphoma in May, 2015. He started chemo immediately, and lived an amazing and atypical 15 months with a great quality of life before succumbing to the disease on August 30, 2016.
Each situation is different, and there are emotional and financial factors that you have to take into account because ultimately, Lymphoma is a systemic disease for which there is no cure. In the simplest of terms, you're buying time. I was advised that with prednisone the expected life would be measured in weeks and with chemo, the prognosis for his type of lymphoma was typically 3-6 months. Predinose treatment cost was discussed in terms of a couple of hundred dollars while chemo was in terms of hundreds of dollars per treatment. The CHOP protocol (most common) is 16 treatments over 24 weeks. Emotionally, you have to prepare yourself. Nightly I prayed for the wisdom and knowledge to make good decisions - and for the strength and courage to actually do what was best for Copper instead of my own desires. I also defined what 'quality of life' meant to me and my 'ideal' scenario for Copper's end of life - and discussed it with his oncologist before we faced it.
I did a lot of internet reading & research, talked with my vet and the oncologist, and ultimately, Copper's age and personality were the primary factors for my decision. (And to be completely honest, since he was a rescue, I wanted to give him a chance to have a good life, for whatever time he had left.) I don't regret the decision - or the money I spent on him - and it was a lot. There were ups and downs, good days and bad days. We met some wonderful people (and dogs) and made some good memories throughout his cancer journey. Copper was blessed to have a fantastic oncologist and oncology team who treated him like "family" and were committed to his quality of life, just as much as I was. I never doubted the quality of care he received because their compassion gave me peace of mind.
If you decide to go with chemo, tests are needed to determine if it's T-Cell or B-Cell lymphoma. Additionally MDR (multi-drug resistance) testing needs to be performed because herding dogs have a genetic predisposition to be sensitive to some of the chemo drugs. The testing will help your oncologist adjust the dosages. Most of the chemo treatments are administered via IV (there's a video either on YouTube or Twitter) but there are some oral chemos drugs as well. Most, if not all, of the chemo drugs are the same ones that people take but dogs tend to tolerate chemo better. There are medications to counteract the side effects: Copper regularly took Metronidazole, Metoclopramide, and Pepcid. Bloodwork is part of every visit to determine if chemo can be administered. It was usually a day or two after chemo that he'd have nausea or diarrhea (if he had them) and it usually only lasted a day or so. Most times he'd come home from chemo and want to play ball.
Food-wise, Copper's oncologist suggested that I feed him a high protein, low carb food (Taste of the Wild was the option I chose). She also suggested giving him a supplement - K9 Immunity Plus (made by Aloha Medicinals) - which he loved. During the last 2 months of his life, Copper's lymph nodes (as part of his physical exam at each chemo session) felt mostly normal but he became very finicky about eating. I switched him to a glass bowl (instead of stainless) which helped for a while. I tried several kinds of dry and canned foods which he'd eat for a couple of days then wouldn't. He liked TurboPup Bars for a while. One week he wanted ketchup on his food (I still laugh about that). Eventually it became whatever I could get him to eat: Ritz Crackers, boiled chicken, ham, turkey meatballs, spaghetti (no sauce), toast with butter, gingersnap cookies, chicken noodle soup, cottage cheese. Lots of trial and error.
When Copper went completely off eating and drinking, we did an ultrasound and determined that the disease had spread to where it was impacting his gastrointestinal tract - though his external physical still didn't show any lymph node enlargements. We gave Copper some pain meds to make him comfortable while waiting for other family members to come say good bye but before they got there, Copper passed away, on his own terms, in his sleep. While his death didn't happen exactly as I'd planned, I was able to spend a little time with Copper before he passed. I like to think it was his way of thanking me for giving him a chance to live a little longer and make some new friends along the way. Copper saved me from having to 'help' him cross over since less than five hours earlier that same day, I had to put my 16 year old rescue, Lacy, to sleep. As hard as it was to lose two dogs on the same day, it was fitting because during the 24 months that Copper was with me, he and Lacy had become good pals. I know she was waiting for him to get to the rainbow bridge so she could play with him and boss him around, just like she used to, despite their age and size differences.
Best wishes for your Baylie.