Do I need to get checked?

I'm(22f) in a relationship with my(20m) bro, we've been together for a little over a year and we're super happy, but he was diagnosed with cancer early 2023 as part of a routine check. Luckily it wasn't bad at all, the doctor said he'd likely recover, and I'm grateful that it was detected early but I'm freaking out a little and I don't know if I should worry or not. I've always had some health issues due to our family history, but I'm scheduled for a check-up anyway and I wanted to know if my dad could have been the one to give him the gene for cancer, or if it's due to something else entirely. He's also not genetically my biological brother, I don't know if it makes a difference, he was adopted when I was 1 and he was 2 and we would've never guessed that he wasn't my biological bro if our parents hadn't told us.