Sister chromatid exchange: variation by age, sex, smoking, and breast cancer status.

Variation in sister chromatid exchange (SCE) frequency in lymphocytes of 125 persons was compared using a multivariate general linear model. The study was performed to determine whether SCE frequency differs with respect to age, sex, smoking, and breast cancer status. Study subjects were divided into: members of two branches of families having an excess of cancer (primarily breast) including a brother and sister in one family who developed nonbreast malignancies within 1 yr of the study; women in both families successfully treated for breast cancer (all at least 5 yr posttreatment); and women from the general population with confirmed breast cancer. Controls consisted of spouses who married into the high-risk kindreds, hospital personnel, and others (primarily tradesmen without history of occupational exposure). Results show that: (1) Women with active breast cancer have a significantly higher mean SCE frequency than control women or women greater than 5 yr posttreatment for breast cancer; (2) Cigarette smokers show a significantly higher number of SCEs than was observed in nonsmokers; (3) The increase in SCE level in smokers is dose-related to exposure as measured by cumulative pack-years; (4) SCE values in both high-risk families are not significantly different from controls; (5) Neither the age nor sex of the individual affects SCE frequency; and (6) The observed distribution of exchanges agrees with that expected based on the proportion of the genome represented by each chromosome group.