Forgive me if I missed it, but what's the evidence the plant's operations actually caused cancer cases? I work for a state cancer registry, and in my experience

Forgive me if I missed it, but what's the evidence the plant's operations actually caused cancer cases? I work for a state cancer registry, and in my experience, reports of potential cancer clusters are rarely shown true. Going by a presentation and the audience's reactions at this year's NAACCR conference, most registries have similar experiences. That's not to say the claims are disproven, but a cancer diagnosis is a rare event, and childhood cancer is an order of magnitude rarer. This is one of those times where "small and biased sample" is a valid criticism.