Cohabitation, infection and breast cancer risk.

For 50 years, the effect of age at first birth (AFB) has been thought to explain the strong association between breast cancer risk and age at first marriage (AFM), which was first reported in 1926. The independent effects of AFM, AFB and number of sexual partners adjusted for parity and other risk factors were estimated in reanalysis of a large international case-control study conducted in 1979 to 1982 (2274 breast cancers, 18209 controls) by unconditional logistic regression. Respective AFB and AFM breast cancer odds ratios (ORs) for ≥31 years relative to ≤18 years were 3.

A case-control study of occupational contact levels in the childhood leukaemia cluster at Seascale, Cumbria, UK.

Objectives: To investigate adult occupational contact levels and risk of childhood leukaemia and non-Hodgkin's lymphoma (LNHL) in Seascale, an association found in other situations of rural population mixing (PM).

Design: Matched case-control study.

Setting: Seascale, Cumbria, UK.

Breast cancer and ages at first marriage and first birth: a new hypothesis.

The aim of this study was to examine available data on breast cancer and age at first marriage from a new perspective: that is, marriage involves the closest contact and contact effects are relevant to the question of infection, a possibility long considered in this disorder. The large Seven Country Study, carried out in 1964-1968, investigated age at first marriage; its reports were examined carefully for details of possible relevance. Intriguing gaps were noted in the grounds for the conclusion by this study that late age at first birth explained an earlier reported association with late age at marriage, with risks presented by age at first marriage for nulliparous, but not for parous, married women.