Pregnancy, breast-cancer risk, and maternal-fetal genetics

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.

Sex of first child and breast cancer survival: a population-based study

Previous reports on the influence of the sex of a child and prognosis of a subsequent breast cancer have been conflicting. We took advantage of a number of large and good quality, nationwide Registries in Sweden to evaluate the prognostic value of the sex of the first child in breast cancer. A population-based cohort of 32,003 women born after 1935 and diagnosed with primary breast cancer between 1958 and 1997 was generated by linking a number of Swedish registries including Swedish Cancer Registry, Cause of Death Registry, Swedish Generation Registry and the Registry of Population and Population changes. Of these, 4,251 were nulliparous, 2,732 had only a boy and 2,497 had only a girl prior to diagnosis. We used this subpopulation to quantify the association between the sex of the first child and breast cancer-specific mortality, using the Cox proportional hazards. Sex of the child did not significantly influence the prognosis of breast cancer. Stratifying by age and adjusting for age at diagnosis, calendar period, time since last birth and age at first child did not alter the results. Our study, the largest up to date, failed to identify evidence to support the proposed association between the sex of the first child and breast cancer survival. Given the previous reports that advocated taking sex of the first child into consideration in making decisions related to breast cancer therapy, our findings are reassuring and clinically important.

The fetal antigen hypothesis: cancers and beyond

Twenty years ago the fetal antigen hypothesis was proposed as a potential mechanism by which women are naturally immunized against cancer antigens by antigens from their fetus. Evidence from recent clinical studies shows that a high percentage of parous woman, but not nulliparous women, show evidence of immunization to antigens found on breast, ovarian and endometrial cancer cells. I suggest that this maternal immunization also affects the fetus, causing early immune rejection of fertilized ova that express cancer-related genotypes. Additional cancers, and perhaps even other types of genetic diseases, may be involved in this mechanism.

The short-term and long-term effect of a pregnancy on breast cancer risk: a prospective study of 802,457 parous Norwegian women

Time-related effects of a pregnancy on breast cancer risk were examined in a population-based prospective study of 802,457 parous Norwegian women aged 20-56 years. The mean follow-up time was 16.4 years. A total of 4787 women were diagnosed with breast cancer. We observed a short-term increase in risk of breast cancer after a full-term pregnancy, with a maximum 3-4 years after delivery, followed by a long-lasting decrease in risk. The maximum risk was about twice the risk for women whose last delivery was 20 or more years previously (incidence rate ratio = 1.99, 95% confidence interval = 1.70-2.33). Compared with nulliparous women, those with one or two children were at higher risk in the first decade after the last pregnancy, whereas those with three or more children were at lower risk in most categories of time since the last birth. The positive association between breast cancer risk and age at last birth was markedly reduced after adjustment for time since last birth. We conclude that there is a non-linear relationship between breast cancer incidence and time since last birth. Part of the relation with age at last birth may be attributed to the association with time since last birth.

Multiple births, sex of children and subsequent breast-cancer risk for the mothers: a prospective study in Norway

Endocrinological changes occurring during pregnancy may influence the subsequent cancer risk of the mother. Further, the endocrinological milieu may differ according to different birth characteristics. In the present study possible relations between multiple births, sex of children and breast-cancer risk were examined in a population-based, prospective study of 802,269 parous Norwegian women aged 20-56 years. A total of 4,782 women were diagnosed with breast cancer during follow-up. Of these, 97 had ever experienced a multiple birth. We found a slightly lower risk of breast cancer among women ever having had a multiple birth than among women with singletons only (IRR = 0.89, 95% CI = 0.73-1.09). The reduction in risk was mainly observed among women with a multiple last birth. Further, the reduction in risk seemed to diminish with increasing parity, and among women with 4 or more full-term pregnancies, ever having had a multiple birth was associated with an elevated risk (IRR = 1.48, 95% CI = 0.97-2.25). The sex of the first or last child did not affect the subsequent breast-cancer risk. Further, we found no associations with the sex distribution among all children or in multiple births, despite a tendency toward a reduced risk among women with several daughters only.

The fetal antigen hypothesis for breast cancer, revisited

The fetal antigen hypothesis was proposed over a decade ago to explain the small, short-term promotional effect, as well as part of the long-term protective effect that pregnancy has on breast cancer risk. The hypothesis is based on immune interaction between mother and fetus, and postulates that breast cancer genes which a women's fetus inherits from her mate may be indirectly involved in protecting the woman against breast cancer. This article addresses new epidemiological data pertaining to the hypothesis plus the growing evidence that prenatal reproductive factors are important determinants of breast cancer risk. It also suggests that iso-immunization from pregnancy, similar to Rh iso-immunization, can produce immunity against breast cancer. The proposed mechanism provides a plan for development of a vaccine against breast cancer. If the fetal antigen hypothesis is valid for breast cancer, the mechanism behind it is likely to apply to other cancers, even cancers that are found in males, since males can be affected be the prenatal component of this mechanism.

Gestational carcinoma of the female breast

Few neoplastic diseases can equal the amazing complexity and sheer perversity of carcinoma of the breast. No doubt as many decades of research lie ahead in its study as already have passed. Clinicians have long appreciated the special relationship of the disease to gestation. Diagnosis and treatment of breast cancer during pregnancy represent only a small part of this fascinating relationship. Although indispensable as research tools, animal models pertain to the human disease only in limited, ill-defined ways. The etiology of human breast cancer remains unclear; chemical, viral, hormonal, genetic, and immunologic theories have all been put forward as possibilities. Although gestation clearly alters both the initiation and growth of mammary tumors, its exact role in the various theoretical considerations remains a mystery. The obstetrician-gynecologist holds an important front-line position in the war against breast cancer, as does any provider of primary care to women, and, indeed, as do women themselves. Rather than decrease vigilance during pregnancy, the physician should pursue with extra vigor any breast mass discovered in the gravid patient, when the clinical examination is even less reliable than usual. The finding of a breast mass usually necessitates biopsy. Except for the inclusion of specific pregnancy-related problems, such as galactocele, the diagnostic spectrum of breast masses removed during pregnancy does not differ from that in nonpregnant women. The discovery of a highly suspicious breast mass, or the confirmed biopsy diagnosis of malignancy, in a pregnant patient should indicate the need for referral to a surgical oncologist versed in this unusual problem. The best approach to gestational breast cancer continues to be the team approach, with consultation from specialists in obstetrics, surgical oncology, anesthesiology, nuclear medicine, radiology, radiation oncology, pathology, and medical oncology. The age and general condition of the patient, the extent of the tumor, the stage of gestation, and the informed opinions of the patient and her spouse help to determine the therapeutic strategy. Careful staging not only guides present therapy but also the therapy of future victims through continued investigation. Most surgeons favor operation without delay if cure seems within reach. Mastectomy, with or without cesarean section, can be accomplished without detriment in the hands of a knowledgeable surgeon-anesthesiologist team. By following certain guidelines, the search for metastasis can be conducted safely and appropriately. The clinical situation occasionally may require the initiation of adjuvant radiotherapy or chemotherapy during pregnancy, by experienced consultants. Ongoing studies of tissue hormone receptors and cell kinetics will continue to give insight into the effects of gestational hormones on breast cancer and can aid in the selection of treatment options for the individual patient...

The management of breast carcinoma in pregnancy and lactation

Until recent years, the prognosis for breast cancer in pregnancy and lactation was regarded as grave. The current new data suggest that pregnant women with early breast carcinoma may be treated in the same way as nonpregnant women without affecting pregnancy. However, women with breast cancer in their first trimester of pregnancy and in whom axillary lymph nodes are involved, should receive chemotherapy and have their pregnancy terminated. Toward the end of pregnancy, adjuvant therapy, when needed, can be delayed until after delivery. In patients with advanced disease pregnancy should be terminated and subsequent treatment initiated. During lactation, diagnosis of breast carcinoma requires suppression of lactation by means other than estrogens. The carcinoma will be treated by standard methods. After radical mastectomy for breast cancer, subsequent pregnancies are allowed but should be delayed until the period of greatest risk has passed.

The influence of pregnancy on breast cancer risk: is it endocrinological or immunological?

Epidemiological data are presented to show that pregnancy is related to a short-term increase in breast cancer risk which precedes its well recognized lower rate for the remainder of life. The data confirm and extend related findings from several earlier studies, and suggest that the biological mechanism which produces the apparent protective effect resulting from pregnancy also produces a short-term adverse effect which is approximately proportionate to the protective effect. This phenomena seems important in terms of what it reveals about the natural history of breast cancer. It is proposed that the general biological mechanism underlying this effect is the immune tolerance during pregnancy which allows the female's immune system to tolerate a fetus whose genes and antigens are partially dissimilar to her own. It is further suggested that the specific mechanism responsible for the phenomena is either a mammary tumor virus or the woman's immune reaction to unidentified fetal antigens that are common to human fetal cells and mammary cancer cells.

Relation between age of mothers with breast cancer and sex of their children

In a consecutive series of 150 women with breast cancer 122 had borne one or more children. Sixty-two patients were aged below 55 years at diagnosis (group A) and 60 were 55 years or older (group B). In group A 91 out of 153 children (59%) were boys compared with 48 out of 141 (34%) in group B (p=0.000007). In group A 54 of the 62 patients (87%) had given birth to one or more boys compared with 35 of the 60 (58%) in group B (p=0.0003). The mean age at diagnosis in mothers of two or more boys was 49.0 years, in those of one boy 55.2 years, and in those of only girls 61.0 years. The differences between each of the mean ages was significant. The mean age at diagnosis in 28 nulliparous patients was 57.7 years. There was no significant correlation between the number of female pregnancies and age at diagnosis. These results suggest that in women liable to develop breast cancer male pregnancies are associated with an early onset of the disease.