No, there are no set limits on how much chemotherapy a patient can receive. However, there are chemotherapy regimens that have been studied and proven effective using particular courses of
treatment. This is why the oncologist will often talk about a certain number of "cycles" for a chemotherapy regimen.
Also, often a particular chemotherapy drug stops being effective after a period of time. At this point, the oncologist may switch to a different type of chemotherapy. Sometimes after awhile the doctor runs out of options. Also, there are times when the oncologist concludes that chemotherapy is not going to be of enough benefit to justify the discomfort of the side effects. If you have a question about chemotherapy regarding your own treatment or that of a loved one, talk to the oncologist openly and ask why she is recommending the course of treatment she's chosen. If she is recommending that you stop treatment, ask her her reasons for this as well. At that point, you may wish to get a second opinion. This can be useful in deciding if you've exhausted all the available treatment options.