The cause of bile duct cancer remains unclear in many cases despite being responsible for the death of more than 10,000 people each year.
"In most of cases, the disease's causes are unknown," said Takao Itoi, an associate professor at Tokyo Medical University.
However, the Health, Labor and Welfare Ministry recently announced there could be a possible connection between the disease and the working environment for staff at printing plants.
Following the recent discovery that some former and current workers of printing companies have higher probability of developing bile duct cancer, the ministry conducted an emergency investigation into 561 printing firms nationwide in June.
Of these plants, 383 were found to have failed to follow rules designed to prevent staff from being poisoned by organic solvents.
Alarmed by the finding, the ministry conducted experiments at a workplace with no windows located in the basement of an Osaka printing firm where 12 current and former workers have developed the cancer.
The ministry found workers there were exposed to chemical substances that had concentration levels 2.6 to 20 times higher than the safety control levels set by a U.S. academic society.
The ministry concluded workers inhaled or absorbed through their skin a high concentration of chemical substances present in the air at the poorly ventilated workplace. Over many years the substances accumulated in the blood of workers, which may have had an effect on the bile duct.
The ministry will conduct an epidemiological investigation into how the chemical substances correlate with the increased likelihood of developing bile duct cancer at a printing firm.
This involved collecting information on bile duct cancer cases from hospitals and dividing patients into two groups: those who worked or are working at printing firms and those in other jobs. The ministry said it will compare the data and analyze it.
The ministry's recent investigation only covered a fraction of the estimated 18,000 printing companies nationwide.
The ministry plans to investigate bile duct cancer cases that are suspected to be related to workplace environments further, which is likely to lead to an increase in the discovery of work-related cases.