First you should distinguish talc contaminated by asbestiform fibres and talc uncontaminated by asbestiform fibres.

The IARC monograph attached deals with the latter. Otherwise see asbestos literature.

Mechanism presumably inflammation leading to cytokine release, free radicas , oxidation of DNA and mutations leading to uncontrolled cell growth.

First you should distinguish talc contaminated by asbestiform fibres and talc uncontaminated by asbestiform fibres.

The IARC monograph attached deals with the latter. Otherwise see asbestos literature.

Mechanism presumably inflammation leading to cytokine release, free radicas , oxidation of DNA and mutations leading to uncontrolled cell growth.

Certainly the main issue to be considered about the problem you pointed out is the presence of asbestos fibers, or not, inside the talc bulk.

Talc ores can be mined both from "acid" stones, containing significant percentages of crystalline silica, i.e. quartz, but no asbestos fibers, and from "basic" stones, often containing asbestos fibers (mainly chrysotile) along with just small quarts percentages. Typical the case of different tal ores in North Western Italy: the ones from Chisone Valley with no asbestos fibers, the ones from Lanzo Valleys (where balangero chrysotile mine operated for decades) with frequent contamination from asbestos fibers and asbestiform fibrous minerals too.

But this is not the unique item to keep in mind; please further consider the possible carcinogenic effect of:

- asbestiform talc as such;

- quartz contaminating talc ores;

- dust as such.

If you are looking for the specific mechanism by which asbestos can lead to cancer, there are several that are proposed:

- Asbestos itself can cause chronic inflammation, leading to repeated cycles of damage and repair.

- The fibres may crosslink, and this can lead to auto-phosphorylation of tyrosine kinases, which then leads to transactivation of proto-oncogenes.

- Asbestos may disrupt mitosis.

- The iron in the asbestos fibres may cause the generation of reactive oxygen species (ROS).

I've worked in mesothelioma (the cancer caused by asbestos) for most of my research career. Here are a couple of go-to reviews of asbestos and mesothelioma:

http://www.nejm.org/doi/full/10.1056/NEJMra050152

Article Malignant mesothelioma