Spousal concordance for cancer incidence - A cohort study

BACKGROUND. Because married couples share at least their home environment, spousal aggregation of cancer might provide clues to unsuspected etiologic factors. The authors sought to measure the concordance of cancer occurrence in married couples and explore factors that might explain greater-than-exp ected concordance. METHODS. The authors identified 25,670 cancer-free married couples in north ern California who were followed for up to 31 years for the development of cancer. In Cox proportional hazards analysis, the development of cancer in a spouse was treated as a time-dependent, independent variable, and spouse- with/spouse-without risk ratios were determined, controlling for age and ge nder. For selected concordant espoused pairs, additional explanatory inform ation was sought in their medical records. RESULTS. There was no excess concordance for all cancers combined; the spou se-with/spouse-without risk ratio was 0.97 (95% confidence interval, 0.90-1 .05). Statistically significant husband-wife associations were found only f or cancer of the tongue and stomach and for non-Hodgkin lymphoma. Except fo r cancer of the penis/endometrium and testis/vulva, based on one couple wit h each combination, gender specific cancers did not aggregate within marrie d couples. Established and suspected risk factors, not necessarily related to the marriage, were found for some individuals who had concordance with t heir spouses. CONCLUSIONS. Little spousal concordance for cancer occurrence was found. Th e study of spousal aggregation does not appear useful in identifying unsusp ected environmental causes of cancer in heterogeneous populations in urban areas of affluent Western countries. A cohort study would have to be much l arger than this one to detect weak spousal concordance reliably. (C) 1999 A merican Cancer Society.