IARC: cancer hazards associated with shiftwork, painting and firefighting

IARC Monographs Programme finds cancer hazards associated with shiftwork, painting and firefighting

After a thorough review and discussion of the published scientific evidence, an expert Working Group convened by the IARC Monographs programme has concluded that
· Shiftwork that involves circadian disruption is probably carcinogenic to humans (Group 2A).
· Occupational exposure as a painter is carcinogenic to humans (Group 1).
· Occupational exposure as a firefighter is possibly carcinogenic to humans (Group 2B).
These three occupations involve complex exposure patterns that make it difficult to attribute risk to specific factors. The Working Group, comprising 24 scientists from 10 countries, met at the International Agency for Research on Cancer (IARC), the cancer research agency of the World Health Organization.
A summary of these conclusions is being published in the December issue of The Lancet Oncology. Full results will be published next year as volume 98 of the IARC Monographs.



Shiftwork that involves circadian disruption is “probably carcinogenic to humans”

Epidemiological studies have found that long-term nightworkers have a higher risk of breast cancer risk than women who do not work at night. These studies have involved mainly nurses and flight attendants. The studies are consistent with animal studies that demonstrate that constant light, dim light at night, or simulated chronic jet lag can substantially increase tumour development. Other experimental studies show that reducing melatonin levels at night increases the incidence or growth of tumours.

These results may be explained by the disruption of the circadian system that is caused by exposure to light at night. This can alter sleep-activity patterns, suppress melatonin production, and disregulate genes involved in tumour development. Among the many different patterns of shiftwork, those that include nightwork are most disruptive to the circadian system.
"Nearly 20% of the working population in Europe and North America is engaged in shiftwork, which is most prevalent in the health-care, industrial, transportation, communications, and hospitality sectors: To date, most studies have focussed on breast cancer in nurses and flight attendants. Now more studies are needed to examine this potential risk in other professions and for other cancers," noted Dr Cogliano, Head of the IARC Monographs Programme.


Occupational exposure as a painter is “carcinogenic to humans”

Epidemiological studies of painters have consistently found small but significant increases in the risk of lung cancer and bladder cancer. In addition, several studies of painters have found increased levels of genetic damage.
Four of five case-control studies found significant increases in childhood leukaemia associated with maternal exposure before or during pregnancy, although findings were inconsistent for lymphatic and haematopoietic cancers in the painters themselves.
Painters are exposed to numerous chemical solvents, pigments, and additives. They can also be exposed to other workplace hazards such as asbestos and crystalline silica. The available information is not specific enough to identify particular agents as the cause of the excess lung or bladder cancers. It also cannot be determined whether the cancer risks have increased or decreased with changes in the solvents, pigments, and additives used in paints.


Occupational exposure as a firefighter is “possibly carcinogenic to humans”

Epidemiologic studies of firefighters have noted excess cancer risks compared with the general population. Consistent patterns are difficult to discern due to the large variations in exposure across different types of fires and different groups of firefighters. Relative risks were consistently increased, however, for three types of cancer: testicular cancer, prostate cancer, and non-Hodgkin lymphoma.

Acute and chronic inflammatory respiratory effects have been noted in firefighters, and this would provide a plausible mechanism for respiratory carcinogenesis. Firefighters are exposed to numerous toxic chemicals, including many known or suspected carcinogens. These intermittent exposures can be intense, and short-term exposure levels can be high for respirable particulate matter and for several carcinogens, notably benzene, benzo[a]pyrene, 1,3-butadiene, and formaldehyde.



What is new, and what do these results mean to me?
"These are IARC’s first evaluations of shiftwork and firefighting. Because there is credible evidence linking these occupations with increased risks of cancer, it is important that further studies be conducted to better identify what it is about such occupations that may increase the risk of cancer so that preventive measures can be implemented to avoid such risks", concluded Dr Peter Boyle, Director of the International Agency for Research on Cancer.

Occupational exposure as a painter has been classified since 1989 as carcinogenic to humans, and this new evaluation has linked painting to lung cancer and bladder cancer. The new evaluation also suggests that maternal exposure may be associated with childhood leukaemia. It is important that further studies be conducted in this area to confirm whether this risk is real and to identify precautionary measures that are appropriate to consider.


(from IARC press release 180a)