Hello I Have A Friend Who Often Tells Me He

hello I have a friend who often tells me he has cancer in the 5 years i have known this man hes had a new form of cancer or a reaccurance of a past cancer and he is telling me he goes through chemo treatmens every couple months over this 5 years... in my mind it says thats way to much chemo for one body but i wanted to ask how many times can one person go through chemo safely