A lot. Most likely, your dog will be put on a protocol which rotates among three or four medications. Chemo drugs vary in cost, and cost will be based on the weight of the dog. Lymphoma is one of the cancers which is most responsive to chemotherapy, particularly if treatment is started immediately. The duration of time a dog will get for a remission is not predictable, but some dogs do quite well for quite a long time. If a dog comes out of remission, it is usually possible to start chemo over again.
I would ask your oncologist about the use of half-body radiation. It has been a few years since I was having a lymphoma dog treated, and half-body radiation was just beginning to be used and showed considerable promise. It is important that that be done as early in treatment as possible, at least that was the recommendation six or seven years ago.
I would suggest you begin a home prepared diet, either raw or cooked (I had no problems with immune suppression and raw even after almost three years of almost continuous chemo). You want to eliminate as much of the carbohydrate as possible. You also might want to do a one-time consult with a holistic vet experienced in dietary supplementation for cancer dogs. There are some medicinal mushrooms and herbs and such which may be very helpful. There are some canine cancer groups on Yahoo which might be resources for you and I also HIGHLY recommend the Yahoo group K9Nutrition (enter it exactly that way in the Yahoogroups search box).
I wish you and your dog all the luck in the world, and will be thinking of you both.
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Don't expect the kind of side effects from chemo that humans experience. Most dogs do not have any adverse responses to the medications at the dosages at which they are used. My dog had a couple of days when she seemed to feel just a little bit punk. She had excellent quality of life during her treatment.