One more comment on this topic.
After starting this thread, I began to wonder if there was one particular breed of dog that was generally considered to be the best choice for the role of therapy dog, in particular for cancer.
After doing some web research I concluded it was rather the case that there are a number of different breeds thought to be especially good at this kind of job.
Here's a listing of some of the leading ones, on a site that would seem to be authoritative on this subject:
www.therapydogcertification.com/5-best-therapy-dog-breeds/But I suppose the best answer is that any good old dog can do the job if he or she has the right personality and "fits in."
(The golden retriever in the first video above would certainly seem to be a great candidate. My nephew owns one who looks exactly like the one in the video above. Her name is Blondie and she is the most gentle-natured dog I have ever known).