Occupational cholangiocarcinoma caused by exposure to 1,2‐dichloropropane and/or dichloromethane

Abstract A cluster of cholangiocarcinoma among printing company workers who were exposed to 1,2‐dichloropropane and/or dichloromethane was classified by the Ministry of Health, Labour and Welfare of Japan on 1 October 2013 as “occupational cholangiocarcinoma”. At the time of the diagnosis of cholangiocarcinoma, levels of γ‐glutamyl transferase, and aspartate and alanine aminotransferases were elevated, and had been elevated in some patients several years prior to the diagnosis. Regional dilatation of intrahepatic bile ducts without tumor‐induced obstruction was characteristic in diagnostic imaging. Pathological examination found chronic bile duct injury with DNA damage, precancerous/preinvasive lesions such as biliary intraepithelial neoplasia and intraductal papillary neoplasm of the bile duct in various sites of the large bile ducts, and invasive cholangiocarcinoma such as mass‐forming type and intraductal growth‐type intrahepatic cholangiocarcinoma and mainly papillary‐type extrahepatic cholangiocarcinoma. Whole‐exome analysis of the cancerous tissues showed hypermutation, substantial strand bias, and unique trinucleotide mutational changes. Patients seemed to suffer high incidence of postoperative complications including intra‐abdominal, which might be related to chronic bile duct injury. Postoperative recurrence from multicentric origins occurred in some patients, as DNA‐injured bile ducts have high carcinogenic potential. Aggressive treatment, including second resections for such multicentric recurrences, appeared to be effective. In 2014, the International Agency for Research on Cancer classified 1,2‐dichloropropane as Group 1 (carcinogenic to humans) and dichloromethane as Group 2A (probably carcinogenic to humans) carcinogens.

elevated in some patients several years prior to the diagnosis. Regional dilatation of intrahepatic bile ducts without tumor-induced obstruction was characteristic in diagnostic imaging. Pathological examination found chronic bile duct injury with DNA damage, precancerous/preinvasive lesions such as biliary intraepithelial neoplasia and intraductal papillary neoplasm of the bile duct in various sites of the large bile ducts, and invasive cholangiocarcinoma such as mass-forming type and intraductal growth-type intrahepatic cholangiocarcinoma and mainly papillary-type extrahepatic cholangiocarcinoma. Wholeexome analysis of the cancerous tissues showed hypermutation, substantial strand bias, and unique trinucleotide mutational changes. Patients seemed to suffer high incidence of postoperative complications including intra-abdominal, which might be related to chronic bile duct injury. Postoperative recurrence from multicentric origins occurred in some patients, as DNA-injured bile ducts have high carcinogenic potential. Aggressive treatment, including second resections for such multicentric recurrences, appeared to be effective. In 2014, the International Agency for Research on Cancer classified 1,2dichloropropane as Group 1 (carcinogenic to humans) and dichloromethane as Group 2A (probably carcinogenic to humans) carcinogens.  3 Currently, 38 patients, some of whom were described in previous reports, are recognized as having occupational CCA. 1,2,4 In the present study, we review the epidemiology, clinicopathological and molecular biological findings, treatments and outcome of occupational CCA, and discuss the mechanism of carcinogenesis. CCA developed in 18 of the 111 workers. All 18 of these patients were exposed to DCP, and 12 were exposed to DCM. When CCA was diagnosed in 17 patients (as of December 2012), the estimated overall standardized incidence rate (SIR) was 1130 (95% confidence interval: 660-810). 5 In addition, CCA incidence increased with cumulative exposure to DCP, which implies an exposure-response relationship. Notably, for cumulative exposure more than 1000 ppm-year, SIR was more than 10 000. 6 Two workers in this company had gastric cancer, one had Bowen's disease, and one had renal carcinoma. Another worker with trichloroethylene exposure developed severe acute hepatitis. 7 Currently, 38 patients are recognized to have occupational CCA; each was exposed to high concentrations of DCP and/or DCP for at least 3 years. [8][9][10] These patients had no other known risk factors for CCA (such as PSC, hepatolithiasis, pancreaticobiliary maljunction, or liver fluke infection).

| CLINICAL FINDINGS, LABORATORY
TEST RESULTS AND DIAGNOSTIC IMAGING The 18 patients from the printing company in Osaka ranged in age from 25 to 48 years old. Their periods of exposure to the chemicals prior to diagnosis of CCA ranged from 6 years, 1 month to 16 years, 1 months (median: 12 years, 6 months). While working at the printing company, some workers suffered from headache, nausea, vomiting, dermatitis, and/or enhanced flare after drinking. CCA was diagnosed in five of the 18 patients when they presented with abdominal pain, jaundice, and/or appetite loss; in 11 patients who had abnormal liver function test results or liver tumors detected during regular health examinations; and in two patients whose liver dysfunction was detected during treatment for other diseases.
At the time of diagnosis, serum c-glutamyl transferase (c-GGT) activity was elevated in all patients, serum activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and serum concentrations of total bilirubin were elevated in most patients. In some patients, serum c-GGT activity gradually increased for several years prior to their CCA diagnosis, followed by increased activities of AST and ALT. 11,12 Such increased c-GGT activity must be related to occupational CCA patients had a higher percentage of regional bile duct dilatation than did patients with non-occupational CCA.
Similar clinical findings, laboratory test results and diagnostic imaging findings were observed in most patients with occupational CCA in Japan. 4

| PATHOLOGICAL FINDINGS
Occupational CCA consists of the mass-forming type of intrahepatic CCA showing well-, moderately or poorly differentiated adenocarcinoma , and the intraductal growth type of intrahepatic CCA and/or papillary-type extrahepatic CCA, showing well-differentiated papillary carcinoma (Figures 3 and 4). In the latter group, invasive cancerous portions were mucinous or tubular adenocarcinoma. 1,4,16 Precancerous/preinvasive lesions, such as biliary intraepithelial neoplasia (BilIN) and intraductal papillary neoplasm of the bile duct (IPNB), were detected in various sites of the large intrahepatic bile ducts and/or hilar bile ducts and peribiliary glands ( Figure 4).
Chronic bile duct injury such as sclerosis of the bile duct with variable inflammatory cell proliferation, biliary epithelial injuries/focal bile duct loss, and biliary epithelial hyperplasia, were also observed in various sites of the bile ducts in the noncancerous hepatic tissues ( Figure 4). When the diagnostic imaging and pathological findings were considered together, regional dilation of the bile ducts without tumor-induced obstruction revealed pathological findings such as BilIN, IPNB, and/or chronic bile duct injury ( Figure 5). 16 Patients with occupational CCA had higher proportions of regional dilatation of the bile ducts without tumor-induced obstruction and precancerous lesions (such as BilIN and IPNB) than did patients with nonoccupational CCA. 14 Immunohistochemical analysis using primary antibodies against S100P and cH2AX to evaluate neoplastic changes and DNA injury gave highly positive results for the cH2AX and S100P markers in invasive carcinoma, BilIN, and IPNB; but positive cH2AX results and negative S100P results for non-neoplastic biliary epithelium ( Figure 6). 16,17 These results indicate that the carcinogenic process Workers with exposure to high concentration of chlorinated organic solvent Liver function tests plus measurement of CA 19-9 and CEA plus ultrasonography CT, MRI/MRCP ERCP with biopsy, cytology Liver biopsy FDG-PET F I G U R E 2 Screening and surveillance of cholangiocarcinoma in workers exposed to chlorinated organic solvents. 12    In mammalian species, metabolism of DCM proceeds through cytochrome P450 (CYP) 2E1, which is abundant in the hepatocytedependent oxidative pathway, 17 producing carbon monoxide and GST T1-1, which is abundant in the bile duct-dependent pathway, 17 resulting in the production of highly reactive intermediates, However, detailed mechanism of carcinogenesis by chlorinated organic solvents is still unclear. In the experimental models using animals, exposure to such chemicals could not induce the CCA.
Further investigations are necessary to elucidate the carcinogenic process.
8 | POLICIES BY JAPANESE GOVERNMENT

AND WHO
As described above, The Ministry of Health, Labour and Welfare of Japan classified CCA as a result of exposure to long-term high concentrations of DCP and/or DCM as an "occupational disease." 3 Treatment cost for occupational CCA can be covered by compensation insurance, and workers who have been exposed to long-term high concentrations of DCP can receive regular health examinations including laboratory tests and diagnostic imaging such as ultrasonography twice a year to detect occupational CCA. Based on the studies, 1,2 in June 2014, IARC reported that DCP was classified as a Group 1 carcinogen (carcinogenic to humans) and DCM was classified as a Group 2A carcinogen (probably carcinogenic to humans). 22 The Japan Society for Occupational Health made similar classifications. 23

ACKNOWLEDG EMENTS
We thank Marla Brunker from Edanz Group for editing a draft of this manuscript.