title: [Age at the time of the first birth: a variable with simple, double, or triple significance in breast cancer studies].
abstract: I.--The inverse relationship of risk with parity is one of the earliest known features of the epidemiology of human mammary cancer. But recently knowledge of this relationship was refined when Mac Mahon and his colleagues found that the protective effect is actually correlated to the age of the mother at the first birth rather than to the total number of children, so that a woman who has a child before the age of 18 is one third as likely to suffer breast cancer in later life as a woman first delivered at 35. II.--A study was undertaken in the Centre Francois Baclesse on the hypothesis that age at first birth may also be related to the age of the patient at clinical onset of the mammary malignancy. One would expect to find a retardative effect of early delivery since this factor was found to be protective as far as mammary cancer risk is concerned. The conclusions of our investigations are in complete opposition to the original hypothesis: in our series, breast cancer appears to occur significantly earlier in women whose first delivery occurred early. III.--Thus the same process appears to be protective as far as total mammary cancer risk is concerned but accelerating as far as age at tumor onset is concerned. These apparently inconsistent observations led to the hypothesis that both studies might express the same biologic process which, in the case of early delivery, inhibits the mechanism of carcinogenic induction and therefore reduces the total number of cancer but which subsequently quickens the evolution of the inducted disease. Such a conjecture implies that breast cancer should be more severe following early first birth. The analysis of our series, as well as the series of Ontario Cancer Clinics, substantiates this hypothesis. But these conclusions are built on indirect proofs or direct proofs which are still short of statistical significance.
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D005260:Female; D005602:France; D006801:Humans; D008875:Middle Aged; D010298:Parity; D011247:Pregnancy; D011336:Probability; D012306:Risk
vernacular_title: L'âge à la première naissance: une variable à la signification simple, double ou triple en cancérologie mammaire