There are occupational mortality studies, that have collected data appropriate for determining whether those engaged in the manufacture or application of heptachlor are at increased risk for dying of cancer, but they have not shown an increased risk of cancer mortality.
Carcinogenicity studies have been identified for rats and mice. These data show increases in tumorigenesis following exposure to heptachlor. The Department of Health and Human Services (DHHS) determined that heptachlor may reasonable be anticipated to be a human carcinogen. The International Agency for Research on Cancer (IARC) determined that heptachlor may possibly cause cancer in humans. According to the U.S. EPA Carcinogen List there is a sufficient evidence of heptachlor 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.