Age of mothers with breast cancer and sex of their children

Parity and susceptibility to cancer

Since fetal antigens are produced by tumour cells and pregnant women may have had contact with certain of these antigens, it is important to establish whether parous women have an altered susceptibility to cancer. Cancers of the breast, ovary and endometrium are less common in parous than nulliparous women. The more children a woman has, the greater is her protection from these cancers. The protection lasts throughout life. The only time when the reverse seems to be true is at childbearing ages, suggesting that in the short term pregnancy may increase cancer risk. There is no direct evidence that pregnancy protects against cancers of non-reproductive sites. Nevertheless, for most sites women have lower incidence rates than do men, and married women have lower rates than single women. The incidence of cancers of the stomach, gall bladder and thyroid, and possibly colon cancer and melanoma, may be increased in parous women (although the evidence is contradictory). Except for stomach cancer, tumours at these sites are more common in women than men. Most of the explanations for the relationship between childbearing and cancer have stressed the role of endocrine and metabolic factors. Immunological factors may well be relevant and need to be taken into consideration in future studies of cancer in human populations.

Progress in understanding breast cancer: epidemiological and biological interactions

Little progress has been made recently in our understanding of the epidemiology of breast cancer. While results from epidemiologic studies regarding reproductive factors remain fairly reproducible from one study to another, other associations such as that between breast cancer risk and dietary fat intake, although biologically plausible, are not consistently found in direct study of humans, while yet other associations, which appear less plausible biologically, become stronger (such as the increased risk associated with modest levels of alcohol consumption). In this paper we attempt to review the epidemiology and biology of breast cancer jointly and describe possible mechanisms of breast cancer induction, the cellular composition of the breast, the epidemiology of breast cancer, and salient biological features, and attempt to reconcile the biology and epidemiology. It becomes obvious that future progress depends on better biological thinking by epidemiologists, and vice-versa. Areas of further research are suggested and discussed, concluding that the ability to measure diet with greater precision could have an important role to play in clarifying our understanding of breast cancer.

Factors associated with age at diagnosis of breast cancer

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