In cancer medicine, the disease we're treating is so serious and the drugs themselves have enough side effects that we know of that the patients are willing to put up with this. So the issue of adverse effects in oncology drugs is not the pressing problem that it might be with more widely used drugs and other diseases.
That said, the most adverse effect is the failure of the drug to work, and that's the one we're concerned with here today, given the expense of these drugs.