A study analyzing mesothelioma incidence rates in Eastern China produced unusual findings, contrasting significantly from statistics of the asbestos-related cancer in the U.S.
Reported incidence rates in China are significantly lower than the U.S.
Only 15 percent of cases examined in the study were linked to asbestos exposure, the overwhelming cause of mesothelioma in most countries around the world.
China’s results are contradictory for a country which remains one of the world’s largest producers and users of the carcinogenic mineral.
Other contrasting findings from the study:
- Peritoneal mesothelioma cases far outnumber the more common pleural type.
- Women are diagnosed more often than men, at a rate of 5 to 1.
- Median age at diagnosis is more than 20 years younger compared to U.S. cases.
“We found that the profile of the patient in China is quite different,” co-author Haining Yang, a researcher for the thoracic oncology program at the University of Hawaii Cancer Center, told Asbestos.com.
The study published December 2016 in JAMA Oncology.
Low Rate of Asbestos Exposure Among Peritoneal Cases
Researchers reviewed mesothelioma cases from two hospitals in Eastern China:
- Zhejiang Cancer Hospital is located in an area where there is no asbestos industry.
- Yuyao People’s Hospital is in an area that manufactures textile asbestos.
Out of 52 confirmed diagnoses, peritoneal mesothelioma, which develops in the protective lining of the abdomen, outnumbered pleural mesothelioma by a 3-1 ratio with 38 cases. This varies greatly from diagnoses in the U.S., where pleural cases account for 75 percent of all mesotheliomas.
The study showed less than half of the peritoneal cases developed in people exposed to asbestos.
“These findings point to a unique opportunity to investigate other causes of peritoneal [mesothelioma] in this population, aside from asbestos,” Weimin Mao, lead author and oncologist at Zhejiang Cancer Hospital, wrote in the study.
Researchers linked an additional five pleural cases and one testicular mesothelioma case to asbestos.
Mesothelioma Higher in Young Chinese Women
The study points out the “unusual prevalence” of malignant mesothelioma in Chinese women.
Women accounted for roughly 80 percent of all mesothelioma cases in the Chinese study.
Historically, mesothelioma is overwhelmingly a male disease, largely because asbestos exposures occur in male-dominated work settings such as construction and industrial work.
But that isn’t the case in Eastern China, especially among women with peritoneal, which accounted for the majority of the cases.
Zhejiang and Yuyao hospitals had a similar number of cases of peritoneal among women (14 and 18, respectively), but vastly different ratios of patients with a history of asbestos exposure:
- Thirteen of 18 peritoneal cases from Yuyao occurred in women exposed to asbestos.
- Only 1 of 14 cases from Zhejiang was associated with exposure.
There were 12 total cases of pleural mesothelioma. Of those, 10 were women and only five had a history of asbestos exposure.
“Except for asbestos exposure, no significant demographic differences were observed between the [Zhejiang] and Yuyao People’s Hospital, suggesting that asbestos may not be the main cause of [malignant mesothelioma] in these women,” Mao wrote in the study.
Age was also a differentiating factor in the study.
The median age of a mesothelioma diagnosis was 50.6 years old, significantly younger than the average age of 72 in the U.S.
Nine cases occurred in people 40 or younger, compared to less than 1 percent in the same age group in the U.S.
The Need for Further Investigation
The incidence rate study in China emphasizes there remains much to learn about the roles asbestos exposure, genetics and other factors contribute to mesothelioma and other cancers. It also shows how these factors might vary in different parts of the world.
Yang and Dr. Michele Carbone at the University of Hawaii Cancer Center have pending patent applications on the BRCA1 associated protein 1 (BAP1), a gene that may play a significant role in a person’s probability of developing mesothelioma.
The study indicates the prevalence of malignant mesothelioma in different regions of China is still unknown. Reported overall incidence rates in China is 1.5 cases per million people, or roughly 2,000 total cases in the world’s most populous country.
Past and present asbestos use in China suggests this number could be far too low.
While China has some regulations in place, the country continues to use chrysotile — also known as “white asbestos” — heavily in construction materials. According to the China Non-Metallic Mineral Industry Association, consumption decreased since peaking in 2012.
Yang noted the cause of the nonasbestos cases in the study needs further investigation.
“It’s all very interesting, but a lot more questions still need to be answered,” Yang said. “That’s a great part of doing research, because there’s always more and more questions you want answered and by the time you answer the questions you improve your knowledge and then you’re more curious to answer the next question.”