The influence of age on DNA labeling index of human breast epithelium

Susceptibility of the mammary gland to carcinogenesis varies with age and is directly related to the proliferative activity of the mammary gland. The purpose of the present study was to analyze the influence of age on the DNA-LI of 15 samples of normal human breast tissue in short term organ culture following a one hour ³H-thymidine pulse. Two groups of patients were studied: young women, ranging in age from 21 to 32 (mean 26.6 years) and older women, ranging in age from 42 to 57 (mean 49.6 years). Differences in the DNA-LI between the two age groups were statistically assessed using the Wilcoxin rank-sum test and contingency table analysis using the Fisher Exact test. Tissues of the younger group consisted of mainly intralobular terminal ducts and alveoli with a mean DNA-LI of 1.00 ± 0.5%. Tissues of the older group consisted of large ducts, intralobular terminal ducts and alveoli with a mean DNA-LI of 0.42 ± 0.7%. The DNA-LI values were significantly lower in the older group (p < .05, Wilcoxin test) than in the younger group.