Population‐based cohort investigations of the risk for malignant tumors in first‐degree relatives and wives of men with breast cancer

Background. Retrospective studies of familial cancer risks could be subjected to bias and should be supplemented with prospective studies if possible. Few such studies exist, and no prospective population‐based study has addressed the risk for malignant tumors among relatives or wives of men with breast cancer. Methods. All first‐degree relatives and wives of 153 men whose conditions were diagnosed as male breast cancer from 1965 to 1989 in the southern health‐care region of Sweden were identified through parish data. Relatives and wives alive January 1, 1958, were included in two cohorts. Their vital status and cancer morbidity were studied in the Swedish Cancer Registry, Cause of Death Registry, and Census Registry. Results. The incidence for malignant tumors was significantly increased among female first‐degree relatives (standardized morbidity ratio [SMR], 1.36). Significantly elevated SMR were seen for breast carcinoma (SMR, 1.80), ovarian carcinoma (SMR, 2.27), and cancer of the parotid gland (SMR, 5.58). Elevated nonsignificant SMR were seen for cancer of the cervix uteri and for bone and soft tissue sarcoma. An almost significant decreased overall cancer incidence was seen for male first‐degree relatives (SMR, 0.75). The most pronounced decrease was seen for cancer of the prostate. The increased breast cancer incidence in female relatives were present in mothers, sisters, and daughters. The overall tumor incidence was not increased (SMR, 0.98) in wives of men with breast cancer. There was no significant increase in breast cancer incidence (SMR, 0.97). Conclusions. Female first‐degree relatives of men with breast cancer have an elevated incidence of breast cancer and other female genital tumors, whereas male first‐degree relatives have a reduced cancer incidence. Wives of men with breast cancer have a similar cancer incidence as the general population.