Help me understand both parents' identical cancer deaths

I've had two non-smoking parents both die at the age of 70 in 2014 and 2017. Each had: - The same type of lung cancer (adenocarcinoma, a on-small cell lung cancer) showing up in the same lung - Both worked in office jobs - It's possible one or both grew up in smoke-filled homes, but that was fairly common at the time. - They moved around several times in their lives, living no longer 5-10 years in any residence. - They were fairly vigilant about checking houses for radon levels. There was a mildly unsafe level in central Pennsylvania where they were living for 6-7 years in their late 50s. That level, however, still registered under what Europe would consider unsafe and it was addressed with a radon extractor fan. One parent worked in the basement level, which was also where my room was as a teen for 5-6 years. The other parent was rarely on that level of the house.

From what I understand this is rare for non-smokers to get this cancer, and extraordinarily rare for both to get it without a shared non-genetic cause even accounting for radon risk.

I'm curious if anyone has any ideas on how to think about this? I'm now in my 30's, but am concerned that if it was radon, that I will have exposure from my teens bear consequences on me later in life. I'm curious if anyone in the hacker news community (analytical/creative types) can think of any explanations for this that go beyond random chance. I'm also curious about who I could talk to about this that would have good context on cancer etiology.