Cancer in Households: A Human-Canine Retrospective Study 2

An index case group of 427 households in which canine malignancies were histopathologically confirmed was matched, on the basis of 5 household human-cancer risk categories, with 520 control households in which dogs were free of malignancies. Of 54 human cancers reported in case households, 48% were verified malignancies; of 39 human cancers reported in control households, 54% were verified. This study, which could detect differences in relative risk in excess of threefold to fourfold, showed no overall association of human and canine cancer. Tests of the highest human risk groups separately—households containing members predominately 60 years of age and over—also were without significance. The small number of verified human and dog malignancies in the same household precluded the analysis of associations of specific tumor histologic types or sites. However, 5 cutaneous malignant melanomas in dogs were associated with malignancies in the digestive tract of humans. While this is possibly a spurious association, it is interesting that most of the 48 canine malignant melanomas in this study were on the head region, the area most in contact with humans.