The finding that air pollution, especially high levels of PM 2.5 in the environment, can induce lung cancer has been widely verified. The International Agency for Research on Cancer (IARC), a division of the World Health Organization, has also classified air pollution as a carcinogen.
Studies have also shown that long-term exposure to high levels of PM 2.5 not only induces lung cancer, but also increases the incidence of hepatocellular carcinoma. Whether it’s lung cancer, liver cancer or other malignancies, “air pollution causes cancer” is a long-term effect.
So what does PM 2.5 mean for people who already have cancer? A recent study found that people with liver cancer who lived in areas with high PM 2.5 concentrations had a greater risk of dying.
Risk of death study of 20,000 liver cancer patients in the United States
This retrospective study was conducted in California, USA, screening information on new liver cancer patients from 2000 to 2009 from the local oncology disease database and pulling PM 2.5 concentrations from the US Environmental Protection Agency’s Air Quality System database for different areas over the same time period.
Because both the presence and extent of liver cancer metastasis are related to the survival time of patients, scientists classified patients according to different degrees of liver cancer (limited liver cancer without metastasis, having developed local metastasis, having developed distant metastasis), calculated all-cause mortality and liver cancer mortality for each type of patient in different PM 2.5 environments, and then analyzed the associated risk ratios.
The study included a total of 20221 patients with liver cancer (mean age 63.7 years), and the median survival time for all patients was only 0.64 years. That means that only half of that many patients with liver cancer lived past 0.64 years, which works out to an average of less than 8 months.
The analysis showed that when PM 2.5 concentrations increased by 5.0 μg/m, the risk ratio for all-cause mortality was 1.18.
That is, if the PM 2.5 concentration level in city A is higher than city B by 5.0 μg/m, then the risk of death for patients with liver cancer in city A will be 1.18 times higher than in city B.
The study also found that this risk ratio was not linear, but rather similar to an exponential relationship. That is, for every further increase of 5.0 μg/m in the PM 2.5 concentration gap, the increased risk of death for liver cancer patients would be more than 1.18 times greater.
In addition, PM 2.5 had a greater impact on the risk of death in patients with limited hepatocellular carcinoma without metastases, and a relatively smaller impact in patients who had developed local metastases and those who had developed distant metastases.
Staying away from PM 2.5 pollution may help patients with liver cancer
Thus we can see that the more polluted the air (higher PM 2.5 concentrations) you live in, the higher the risk of death for liver cancer patients.
However, there are some confounding factors that are difficult to rule out in this study, such as the fact that people living in environments with high PM 2.5 concentrations are mostly economically disadvantaged and are likely to be diagnosed with advanced liver cancer at the time of detection and thus have a higher risk of death compared to other areas. Other confounding factors may also be present, leading to less reliable study results.
Therefore, the results of this study need to be further confirmed and should be viewed with caution, not to mention increased fear.
However, the results of the study are a reminder that people with liver cancer need to be more protected from PM 2.5 and avoid going outside when the air quality is poor.
Also, PM 2.5 has been shown to be carcinogenic, and it is important to do what we can to improve our living environment to protect human health, which is something we all need to do.