A study, published this week, in the British Medical Journal, Occupational and Environmental Medicine, has reported that exposure to asbestos may be a risk factor for cholangiocarcinoma (CC).[i]
CC is a rare cancer of the bile ducts, which are small tubes that connect the liver and small intestine. The function of the bile ducts is to allow a fluid called bile to flow from the liver to the intestine, where it aids digestion.
The incidence rate of CC in England is around 3.58 per 100,000 per year, and the mortality rate is around 3.64 per 100,000 per year (the mortality rate appears higher than the incidence rate because CC used to be classified differently prior to 2010).[ii] It has been reported that incidence appears be to be increasing in the Western World.[iii] As it is rare, survival statistics are more difficult to estimate when compared with other, more common cancers.[iv] In England, in 2012, 30% of men and 25% of women survived for a year after diagnosis, while more than 5% of men and around 5% of women survived for 5 years post-diagnosis.
Risk factors for CC include age, various medical conditions, and exposure to the medical dye known as thorotrast. Treatment options include surgery, chemotherapy and radiotherapy. CC can be divided into two sub-types: intrahepatic bile duct cancer (ICC), which starts in the liver, and extrahepatic bile duct cancer (ECC), which starts outside the liver. In the latest study, these two types were treated separately.
The study involved investigation of 1458 ICC cases and 3972 ECC cases, affecting subjects born after 1920 in Finland, Iceland, Norway and Sweden. Each case was compared with 5 controls who were of the same gender, had the same birth year and stated the same nationality as the test case. Cumulative exposure to asbestos was assessed by considering the participants’ occupations, taken from census data, collected since 1960.
Researchers found an increasing risk of ICC with cumulative exposure to asbestos, with an odds ratio of 1.7 for those with the highest exposures. No association was observed between cumulative asbestos exposure and ECC.
The researchers concluded that the study provides evidence that exposure to asbestos may be a risk factor for ICC, and that there is either no association or a weaker association between asbestos and ECC.
To their knowledge, there is only one other study that has specifically investigated the role of asbestos in the development of CC[v]. The earlier study had limitations including a small number of cases and crude exposure assessment. Further studies of asbestos-exposed cohorts are required to establish whether the association between asbestos and ICC is causal, and to investigate the magnitude of the risk.
[i] Farioli, A. et al. Occupational exposure to asbestos and risk of cholangiocarcinoma: a population-based case–control study in four Nordic countries. Occup Environ Med oemed-2017-104603 (2017). doi:10.1136/oemed-2017-104603 <http://oem.bmj.com/content/early/2017/11/13/oemed-2017-104603?papetoc> accessed 15 November 2017.
[ii] Cholangiocarcinoma mortality higher than incidence? AMMF The Cholangiocarcinoma Charity. <http://ammf.org.uk/2015/06/25/cholangiocarcinoma-mortality-higher-than-incidence/> accessed 15 November 2017.
[iii] Bergquist, A. & von Seth, E. Epidemiology of cholangiocarcinoma. Best Practice & Research Clinical Gastroenterology 29, 221–232 (2015). <http://www.sciencedirect.com/science/article/pii/S1521691815000190> accessed 15 November 2017.
[iv] Bile duct cancer: Survival <http://www.cancerresearchuk.org/about-cancer/bile-duct-cancer/survival> accessed 15 November 2017.
[v] Brandi, G. et al. Asbestos: a hidden player behind the cholangiocarcinoma increase? Findings from a case–control analysis. Cancer Causes Control 24, 911–918 (2013). https://link.springer.com/article/10.1007%2Fs10552-013-0167-3> accessed 15 November 2017.