By Mahita Gajanan/New York
Environmental factors are overwhelmingly to blame for some forms of cancer, according to a new study.
Among the contributors are diet, sun exposure, UV radiation, tobacco, alcohol, the human papilloma virus and hepatitis B and C. These factors impacted between 70% and 90% of several types of cancer, including lung, colorectal, skin, and cervical, said Yusuf Hannun, a cancer researcher at Stony Brook University in New York.
These high percentage risk factors “provide direct evidence that environmental factors play important roles in cancer incidence and they are modifiable through lifestyle changes and/or vaccinations,” the researchers wrote.
Hannun said people should take responsibility to avoid known risk factors, such as smoking and UV radiation. However, apart from the previously established ones, other, more specific risk factors are still unknown. Hannun said he recommended more research to identify specific ones.
The study, published in the journal Nature, also found that rates of certain cancers have been steadily increasing, including melanoma, thyroid, kidney, liver and testicular. Risk of lung cancer also showed a significant increase.
“These substantial increases in incidence suggest that large risk proportions are attributable to changing environments,” researchers wrote.
They cited smoking and air pollutants for the roles they play in developing the risk of lung cancer.
Changing location was also strongly linked to increased risk of cancer in the study.
Data showed that people who migrated from regions of lower cancer risk to those with higher cancer risk soon developed disease at rates consistent with their new environment.
“All these geographic and time dependent changes really speak to the external factor,” Hannun said.
Western Europe, for example, has the highest incidence rate of breast cancer, which is five times higher than rates in eastern Asia and middle Africa. Australia and New Zealand report the highest cases of prostate cancer, which is almost 25 times higher than rates in south-central Asia.
According to the study, no single risk factor can account for why the environments in western Europe and Australia and New Zealand contribute to higher rates of breast and prostate cancers. Researchers suggested both cancers have “complex mechanisms for their aetiologies”.
Hannun cited other examples of cancer “hot pockets” around the world - esophageal cancer is widespread in central Asia and northern China, kidney cancer abounds in eastern Europe and eastern Asia. Cases of gastric cancer in Japan were traced to specific foods, including over cured fish, Hannun said.
Researchers found that the more stem-cell divisions that occurred in a given tissue over a lifetime, the more likely it was to become cancerous. They said that though some cancers clearly had strong outside links - such as liver cancers caused by hepatitis C or lung cancer resulting from smoking - there were others for which the variation was explained mainly by defects in stem-cell division. In those cases, they argued, early detection and treatment would be more effective than prevention.
“The general public needs to understand that people are working on several aspects of cancer and it’s important to figure out how cancers are initiated, and how our environmental factors come into play,” Hannun said. - Guardian News & Media
