Lifting weights after cancer treatment.?

So I'm an ex cancer patient, that has been cancer free for 10 years. I went to see my Oncologist the other day, beforehand he told me NOT to lift weights. I disregarded this and lifted anyways. I been lifting weights since I was 14 (basically a year or 2 after cancer) now I'm 22, as of now no problems at all. He told me there was a certain medicine I forgot the name, makes my heart flabby later in life and cause heart failure. Since I'm older now and well, understand things more ... can I still lift but not as heavy? I want more opinions and such. Mind you, I don't drink, smoke, my diet is beyond strict, and I'm on multi vitamins ... this kinda sadden me because I don't want my life endangered when I'm at middle age .... I also don't want to stop working out, I have fears of losing my body and its a good way de-stress myself. I know this is long, but if you read and answered this THANK you so much in advance :(