One might ask why asbestos causes mesothelioma. Maybe the mechanisms are similar. Although talc is obviously less effective. But if there's increased risk, the lack of mechanistic understanding doesn't negate the evidence.
We already know why asbestos causes mesothelioma. Asbestos can form very small particles that go deep into the lung (there is good relationship between particle size and how deep it penetrates into the lung). Asbestos contains iron and the iron can promote free-radical formation, thus DNA damage and thus cancer. Yes, I'm simplifying it, but that's what I remember from my toxicology classes long ago.
I don't think it's odd to question the toxicity of talcum powder. Talcum powder used to contain asbestos, but doesn't any longer. We have good evidence that the newer talc doesn't cause lung cancer.
So an obvious question is, if talc doesn't cause lung cancer, why would it cause ovarian cancer? Of course, different tissue, different effect, but it raises doubt.
Maybe talc does cause ovarian cancer by some as-yet-discovered mechanism, but I wouldn't blame anyone for thinking it either coincidental (lots of people get ovarian cancer who never use talc) or due to something else.
I was under the impression that the cause was chronic inflammation resulting from recruitment and activation of macrophages and other immune cells to site of the fibres [1]. Chronic inflammation causes cancer on its own independent of external factors like free radical formation.
Well, I should have added details. You are correct that asbestos that doesn't contain iron can still cause cancer through a hypothesized inflammatory mechanism.
Honestly, I don't we know the exact mechanism, but have some theories that seem to fit.
And that, perhaps cryptically, was my point. Why should any chemically inert mineral cause cancer? But some apparently do, regardless. Inflammation seems most plausible.
