Global health experts have moved use of sunbeds and exposure to ultraviolet radiation (including sun exposure) to the highest risk category for causing cancer: they now join agents such as tobacco, asbestos and benzene in being classed as “carcinogenic to humans” whereas before they were classed as “probably carcinogenic”.
The move follows a new report reviewing available research that found that starting to use sunbeds before the age of 30 increased a person’s risk of developing the deadliest form of skin cancer by 75 per cent. Other agents have also been moved to the highest risk category following the report.
The findings that led to the decision by the World Health Organization (WHO) International Agency for Research on Cancer (IARC) to reclassify the cancer risk of sunbeds, ultraviolet (UV) radiation, and other agents, are published in a Special Report in the August issue of The Lancet Oncology.
The report was written by Dr Fatiha El Ghissassi and other IARC members based in Lyon, France, on behalf of the WHO IARC Monograph Working Group.
The IARC reviews the latest research and assigns one of five risk categories to different agents such as chemicals and types of radiation as follows:
- Group 1: The agent is carcinogenic to humans.
- Group 2A: The agent is probably carcinogenic to humans.
- Group 2B: The agent is possibly carcinogenic to humans.
- Group 3: The agent is not classifiable as to its carcinogenicity to humans.
- Group 4: The agent is probably not carcinogenic to humans.
The IARC panel that met to review the evidence that led to the new Group 1 classifications comprised 20 experts from 9 countries. Their meeting was in June this year, and they also identified the tumour sites and mechanisms of carcinogenesis of the agents.
Their assessments will be published as part D of Volume 100 of the IARC Monographs.
The Special Report describes why sunlamps and sunbeds, and UV radiation, which were previously classified as Group 2A: “The agent is probably carcinogenic to humans”, are now in the highest group, Group 1: “The agent is carcinogenic to humans”.
The authors said people in many developed countries now make regular use ultraviolet radiation (UV) emitting tanning devices such as sunbeds and sunlamps, especially young women.
As a result of a “comprehensive meta-analysis” of the available research, they concluded that:
“The risk of skin melanoma is increased by 75 per cent when use of tanning devices starts before 30 years of age.”
A meta-analysis is a way of pooling the results of several studies and analysing the data as if it came from one large study. Researchers using this method also have strict criteria for including and excluding studies: for instance if its design is questionable then a study is left out of the analysis.
El Ghissassi and colleagues also referred to several case-control studies that provided consistent evidence that there was a strong link beween the use of UV tanning devices and melanoma of the eye.
Radiation from the sun is the main source of human exposure to UV radiation, which comprises UVA, UVB and UVC rays.
95 per cent of solar radiation that reaches the earth’s surface is UVA, the other 5 per cent is UVB, while UVC is blocked by the atmosphere’s stratospheric layer.
The authors wrote that:
“Epidemiological studies have established a causal association between exposure to solar radiation and all major types of skin cancer.”
Also, until now, it was thought that the gene mutation that is caused by UV radiation from the sun was caused only by UVB rays, but experiments on mice have shown that UVA can also cause the mutation and skin tumours. Thus the IARC has moved UV radiation as a whole (UVA, UVB and UVC) to Group 1. These were all in Group 2 before.
Welders came under special attention in the report, but the authors were not able to conclude from the evidence available if the occurrence of melanoma of the eye in that group was as a result of UV radiation alone, or other agents or both. The authors said:
“A full review of the carcinogenic hazards of welding will be undertaken with high priority.”
The IARC has also moved all types of ionising radiation into Group 1. This was the first time that all types of ionising radiation have been reviewed by one team of experts.
Ionising radiation includes:
- Radon gas, which damages the lungs. It can seep from soil, rocks and building materials. The Special Report says radon gas is the second leading cause of lung cancer after tobacco smoke.
- Plutonium and its decay products. These affect the bones, liver and lungs of people who work with plutonium, for instance in nuclear plants.
- Radium and its decay products. These affect the bones of patients being treated with radium, for instance for prostate and other cancers.
- Phosphorous-32 and its decay products. These cause acute leukaemia in medical patients (phosphorous-32 is used for example to treat inoperable cancer tumors).
- Radioiodines (radioactive isotopes of iodine). These can cause thyroid cancer in children and adolescent survivors of nuclear reactor accidents or who are exposed to fallout from nuclear tests.
“A review of human carcinogens — Part D: radiation.”
Fatiha El Ghissassi, Robert Baan, Kurt Straif, Yann Grosse, Béatrice Secretan, Véronique Bouvard, Lamia Benbrahim-Tallaa, Neela Guha, Crystal Freeman, Laurent Galichet, Vincent Cogliano, on behalf of the WHO International Agency for Research on Cancer Monograph Working Group
Sources: The Lancet Oncology, WHO.
Written by: Catharine Paddock, PhD