Multiple times but I think the worst was when I was around 12.

I had gone into the hospital with appendicitis, three days of the doctor's not having any fucking idea that I had appendicits, and finally the surgery. Turns out I was lucky as fuck, my appendix reptured seconds after being on the surgery table. A week later of recovery, I have to visit the surgeon for a "checkup", only to have the bombshell dropped I had carcinoid tumor in my appendix. Long story short, I was told I had cancer, then told I was cured with cancer. Now I like to think when I was twelve I was a little too mature, I grew up too fast because of reasons I'd rather not go into, but that day, fuck dude. Just, I remember sorta just staring at the wall, doc talked about the annual scans I'd have to deal with. I held in my tears, but I was a twelve year old girl just told I had cancer and there were high rates it'd return. I was quiet and probably looked like I was about to cry, because my mom held my hand, then I just sorta broke down. I screamed and sobbed like a toddler, clinging onto her. I can't remember much afterword, since it was a while I just know after a while I began hyperventilating and passed out.

TLDR: 12 year old told they had cancer, sobbed like a baby, then passed out.