Why is silica associated with lung cancer?

RCS causes lung cancer by an indirect mode of action via inflammation, i.e. silicosis, thus minimising silicosis risk will also minimise or even eradicate lung cancer risk due to RCS.

This is the outcome of a recent hazard assessment of Respirable Crystalline Silica health effects which has been commissioned to a team of scientific experts. Two reports were produced:

  • Review and Hazard Assessment of the Health Effects of Respirable Crystalline Silica (RCS) Exposure to inform Classification and Labelling under the Global Harmonised System: Overview Report (Borm P, Brown T, Donaldson K, Rushton L, 2009); and
  • Review of the Literature of the Health Effects of Occupational Exposure to Crystalline Silica: Silicosis, Cancer and Autoimmune Diseases (Brown T, Rushton L, 2009)

A summary of these reports by Dr Peter Morfeld (Institute for Occupational Medicine of Cologne University, Institute for Occupational Epidemiology and Risk Assessment of Evonik Industries, Essen, Germany) is available at the following link.

A suspicion of lung cancer occurrence among workers exposed to crystalline silica was evoked at the end of the 1960s. However, confirmation of a link between silica exposure and lung cancer was generally considered impossible until the 1980s. In 1987, the International Agency for Research on Cancer (IARC) evaluated crystalline silica as a probable human carcinogen (Group 2A – sufficient evidence in animals but limited evidence in humans). This opinion was based upon the findings that under laboratory conditions some quartz samples could be carcinogenic for rats (but not for other rodent species).

Over the next decade, no further conclusive human evidence was brought forward but experts agreed that an excess of lung cancer could be observed in silicotics (i.e. people already having silicosis).

In 1997, the IARC re-evaluated crystalline silica and concluded on the basis of literature review that inhaled respirable crystalline silica from occupational sources is carcinogenic to humans. See question 1.12.