Did Bruce receive treatment for cancer in "Bang the Drum Slowly"?
I think it is safe to assume that Bruce did receive whatever treatments were standard at the time for cancer.
Your question is a good one, because the book really does not go into any detail at all about any of the treatments Bruce might have received. Besides the fact that the intricacies of his medical condition are not the main focus of the narrative, it is important to keep in mind that the story takes place in 1955, and although I am no expert on medicine, I think it should be noted that medical treatment of cancer, and Hodgkins' Disease in particular, would not have been nearly as advanced as it is today, and most likely would have been focused on symptom management more than a cure.
The book does give us a few indications that Bruce did receive treatment for his disease. Henry "Author" Wiggen learns of his friend's condition when he gets a call from Bruce to pick him up in the hospital, and when Henry talks to the doctor, the doctor tells him, "We are only human and cannot do everything". Bruce also notes that he is "covered by North Pole coverage...it is all paid right down to the end", which is a reference to insurance he has bought which will assumably pay for his treatment until he dies (Chapter 1). Another indication that Bruce receives treatment is that in each city they play in, Henry is careful to get "the names of all the doctors" in the area ahead of time, in case they should be needed.