Being diagnosed with cancer during pregnancy or while breastfeeding is not associated with increased risk of cancer-related death – with the exception of breast and ovarian cancer diagnosed during lactation, according to a study of women in Norway.
The question of how pregnancy affects cancer has been debated for decades. Historically, it was thought that higher levels of the female hormone oestrogen, which occur during pregnancy, might increase the aggressiveness of cancers that can be hormone-dependent, such as breast and ovarian cancer, and also malignant melanoma. Other changes that occur during pregnancy, including suppression of the immune system and increased vascularisation, might also have adverse effects on tumour development.
Some previous studies have suggested decreased survival in women with breast cancer or malignant melanoma diagnosed during, or shortly after, pregnancy. However, results have been contradictory.
To explore the issue more carefully, researchers analysed survival in all women aged 16 to 49 years in Norway diagnosed with cancer between 1967 and 2002. They compared survival in women who were pregnant or breastfeeding when diagnosed with the most common cancers in this age group – including breast, cervical, ovarian and thyroid cancers, malignant melanoma, brain tumours, malignant lymphoma and leukaemia – with those who were not.
The impact of pregnancy and lactation on survival from cancer is becoming increasingly important as women have children at an older age, and cancer incidence also increases with age. In Norway, more than half of all pregnancies now occur in women aged 30 to 49 years, compared with 24% in 1967. The rate of cancer in this age group is also increasing – so there are growing numbers of women who are diagnosed with cancer during pregnancy or lactation.
The retrospective, population-based cohort study analysed data on 42,511 women from the Cancer Registry and the Medical Birth Registry of Norway. Results for all cancers combined showed no effect of being diagnosed with cancer during pregnancy (hazard ratio [HR] 1.03; 95% confidence interval [CI] 0.86 to 1.22) or during lactation (HR 1.02; 95% CI 0.86 to 1.22) on survival.
In contrast, women with breast cancer diagnosed during lactation were nearly twice as likely to die from their breast cancer as women who were not breastfeeding (HR 1.95; 95% CI 1.36 to 2.78; p
The researchers, led by Hanne Stensheim, from the Cancer Registry of Norway, Oslo, said: “For all sites combined, we found no increased risk of cause-specific death in 1,047 women with their first cancer diagnosed during pregnancy or lactation. However, in the subgroups of lactating women diagnosed with breast or ovarian cancer, the risk of cause-specific deaths was doubled. The risk was also slightly elevated in women diagnosed with malignant melanoma during pregnancy.”
They advised: “Detection of breast cancer or ovarian cancer during lactation and malignant melanoma during pregnancy requires particular awareness by health care professionals.”
The worse outcomes for breast cancer in women who are breastfeeding may be due to delay in diagnosis and treatment, the researchers suggested, because changes or lumps in the breast during lactation may be regarded as normal by both women and doctors. Mammograms are also difficult to interpret during these stages of a woman’s life.
A negative effect of oestrogen on tumours seemed unlikely, the researchers suggested, because poorer survival was seen only in women diagnosed with cancers during lactation but not in those diagnosed while pregnant.
The researchers discovered a ‘healthy mother effect,’ in which women diagnosed with cancer after a pregnancy had a reduced risk of dying from their cancer, for all cancers combined (HR 0.49; 95% CI 0.41 to 0.59). Compared with women without a subsequent pregnancy, women with postcancer pregnancies and a diagnosis of cervical cancer, lymphoma or leukaemia, had approximately 80% lower risk of cause-specific death. The researchers explained that this implied self-selection among women who had undergone cancer treatment, whether they choose to get pregnant afterward or not.
One limitation of the study was that the numbers of women diagnosed with cancer during pregnancy or lactation were small. Just over one in every hundred cancers included in the study were in pregnant women (n=516; 1.2%) and in lactating women (n=531; 1.2%). Tracking the incidence of cancers diagnosed during pregnancy and lactation over time showed a slight increase during the study period (annual increase of 2.5% and 1.6%, respectively).
Commenting on the study, Fedro Alessandro Peccatori, Director of the Unit of Allogeneic Transplantation, Milan, Italy, noted: “Most data about pregnancy associated cancer prognosis derive from retrospective case-control studies or from prospective cohort studies of selected countries or regions. Not everywhere is able to cross link data on the whole population for cancer diagnosis and childbirth, nor is it feasible to follow women throughout their lives with specific and reliable information about the cause of death. However, this was possible in Norway, a country with less than five million inhabitants with a 55-year-old cancer registry and a birth registry established in 1967.”
He considered that the most important finding of the study was that, overall, cancers occurring during pregnancy or lactation do not have a worse prognosis compared to cancers diagnosed at other times, when adjusted for age, diagnostic period and initial disease extent.
When the results were categorised by histology, Doctor Peccatori noted that breast cancer diagnosed after a recent childbirth had a significantly worse prognosis. “These data are in line with recent reports1 and can be explained by a higher incidence of oestrogen receptor negative and lymph node positive tumour2.”
Having a pregnancy after cancer diagnosis (the median time from diagnosis to subsequent pregnancy in this study was 3.5 years) does not increase the risk of death, which is halved overall, he said. “This is coherent with previous studies and confirms the ‘healthy mother effect’, i.e. that women who have pregnancies after cancer are self selected for better prognosis.”
Doctor Peccatori considered it interesting that only a few women (5.7%) had pregnancies after cancer diagnosis, even though the follow-up was quite long (15.2 years). The data also showed large variations according to tumour type: 21% of women gave birth after having thyroid cancer or melanoma, while only 138 of 13,073 women (1%) gave birth after having had breast cancer. “This may reflect the gonadal toxicity of the treatments administered for breast cancer, but also the misleading information given to patients that a subsequent pregnancy after breast cancer may negatively influence survival,” he said. “On the contrary, all the published data (including the present study) do not describe an increased risk of mortality for these patients3.”
“This paper gives physicians treating pregnancy-associated cancers and women who wish to conceive after cancer diagnosis precious information and reassurance,” Doctor Peccatori considered. “The prognosis for most tumours diagnosed during pregnancy is no worse than for cancers diagnosed outside pregnancy, but awareness about the possibility that pregnancy and lactation can be complicated by cancer is warranted,” he suggested. “Unfortunately, too many cancers are still diagnosed during pregnancy and lactation in advanced stages, with overall worse prognosis.”
Reference
Stensheim H, Moller B, van Dijk T, and Fossa SD. Cause-specific survival for women diagnosed with cancer during pregnancy or lactation: a registry-based cohort study. Journal of Clinical Oncology 2008; jco.ascopubs/cgi/doi/10.1200/JCO.2008.17.4110
References cited in the research summary
Olson SH, Zauber AG, Tang J, et al. Relation of time since last birth and parity to survival of young women with breast cancer. Epidemiology 1998; 9: 669-671
Phillips K-A, Milne RL, Friedlander ML, et al. Prognosis of Premenopausal Breast Cancer and Childbirth Prior to Diagnosis. Journal of Clinical Oncology 2004; 22:699-705
Peccatori F, Cinieri S, Orlando L, Bellettini G. Subsequent pregnancy after breast cancer. Recent Results Cancer Res. 2008;178: 57-67
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