Data from people exposed to hexachlorobenzene by inhalation provide weak evidence for an association between exposure to hexachlorobenzene and cancer of the thyroid, brain, and liver, while very limited data from orally exposed people showed no increase in cancer risk. One casecontrol study associated elevated adipose levels of hexachlorobenzene with increased risk of breast cancer, but other casecontrol studies have not found any relationship between body burdens of hexachlorobenzene and breast cancer, bone sarcoma, or leukemia. The available epidemiology reports taken together do not support an association between hexachlorobenzene exposure and increased cancer incidence, but their limitations preclude considering them evidence of noncarcinogenicity. Because hexachlorobenzene produces porphyria, it is noteworthy that several human studies have associated porphyria with increased incidence of liver cancer.
Several animal studies have demonstrated that oral exposure to hexachlorobenzene increases the incidence of tumor formation. The evidence of carcinogenicity is strongest in the liver. Additionally, exposure to hexachlorobenzene has been shown to induce renal metaplasia, adenomas, and renal cell carcinomas (in rats, mice, and hamsters); lymphosarcomas (in rats, mice, and hamsters); adrenal hyperplasia and pheochromocytoma (in rats); parathyroid adenomas in rats); and hemangioendothelioma and thyroid tumors (in hamsters). No animal cancer bioassays by inhalation or dermal exposure were located.
Based on these findings in animals, hexachlorobenzene is considered a probable human carcinogen.
The Department of Health and Human Services (DHHS) determined that HCB may reasonable be anticipated to be a human carcinogen. The International Agency for Research on Cancer (IARC) determined that HCB may possibly cause cancer in humans. According to the U.S. EPA Carcinogen List there is a sufficient evidence of HCB carcinogenicity from animal studies with inadequate or no data from epidemiologic studies in humans, there for it is classified as a Category B2, Probable human carcinogen.