The system isn't set up to answer or ask the question "did it specifically cause this cancer", because that question is known to be unanswerable.
I'm curious how you draw this conclusion. While many substances may not, with 100% reproduction rates, cause a particular response there can be a majority that happens when excessive or improper exposure happens. If you're saying the question is unanswerable because it's not 100% guaranteed you'll get cancer, but say 67% chance then that's proof it did cause cancer in the subset. In this case it appears there has been suppressed study data which points directly to the outcome which brings into question, for the jury, the morality of the organization selling the product which are likely influencing reference points for a jury.
That seems decidable.
- The age-adjusted baseline rate of a particular type of cancer is, say, 1%.
- An age-adjusted 2.5% of people in an afflicted community have been diagnosed with this type of cancer. This is a huge increase above baseline.
- By implication, of people in the community with a diagnosis of this type of cancer, 40% of them would have cancer anyway for reasons unrelated to whatever is being sued over, and 60% of them got it "because" of whatever the problem is.
It isn't possible to make any distinction between those groups at the level of an individual case. There's no difference in the cancer.
https://en.wikipedia.org/wiki/McGhee_v_National_Coal_Board
Your jurisdiction might deal with things differently, but this case has had international adoption, as the framework deals with scientific uncertainty fairly elegantly.