medwireNews: Two independent studies shed light on the effects of pregnancy during cancer, one finding that pregnancy does not adversely affect the survival of women with breast cancer and the other showing an association between maternal cancer and an increased risk for stillbirth and neonatal mortality.
The first study, published in JAMA Oncology, used data drawn from linked health administrative databases in Ontario, Canada, on 7553 women aged 20–45 years who were diagnosed with invasive breast cancer between 2003 and 2014.
The 5-year actuarial survival rates for the 5832 women who had no pregnancy (including abortions, live births, and stillbirths), the 1108 women who were pregnant before diagnosis (defined as conception between 5 years to a year prior to the index date), and the 501 with pregnancy-associated breast cancer (conception between 11 months prior to and 21 months after diagnosis) were 87.5%, 85.3%, and 82.1%, respectively.
And fewer than six of the 112 women in the pregnancy after breast cancer group (defined as conception 22–60 months after the index date) died during an average follow-up of 5.2 years, report Steven Narod (University of Toronto, Ontario) and co-researchers.
After adjusting for age and other factors – such as year of diagnosis, tumor stage, hormone receptor status, and treatment type – there was no significant increase in the all-cause mortality risk for women pregnant before or simultaneous with breast cancer versus those with no pregnancy.
Of note, a time-dependent analysis showed that patients who gave birth at least 6 months after the index date of breast cancer diagnosis had a significantly lower mortality risk than nonpregnant patients, with 5-year actuarial survival rates of 96.7% versus 87.5% and age- and multivariable-adjusted hazard ratios of 0.22 and 0.25, respectively.
Narod et al summarize that “[p]regnancy around the time of, or after, diagnosis of breast cancer, does not worsen survival,” adding: “For breast cancer survivors who wish to conceive, the risk of death is lowest if pregnancy occurs 6 months or more after diagnosis.”
But they acknowledge that “[t]he apparent survival benefit in women with pregnancy following breast cancer (vs nonpregnant women) might be owing to some degree of the so-called healthy mother effect, in which women who conceive are most likely to be a self-selected group of healthy women with better prognoses.”
The second study, an analysis of nearly 4 million singleton births in Sweden between 1973 and 2012, appeared in the Journal of Clinical Oncology.
Using data from the Swedish Medical Birth Register and the nationwide Cancer Register, the team found a significant association between maternal cancer diagnosed during pregnancy (n=984) and stillbirths, an association driven mainly by stillbirths considered small-for-gestational-age (SGA). Compared with women not diagnosed with cancer during or the year after pregnancy (n=3,943,508), the corresponding incidence rate ratios (IRRs) for all stillbirths and those considered SGA were 2.5 and 4.9.
Such an association with stillbirth was not observed for women whose cancer was diagnosed the year after pregnancy (n=2723).
But the risk for neonatal (0–27 days) mortality was significantly increased for women diagnosed with cancer when pregnant or in the following year relative to controls, with IRRs of 2.7 and 2.0, respectively, as was the risk for preterm births, with respective IRRs of 5.8 and 1.6.
Mediation analysis showed that preterms births accounted for 89% of the association between cancer during pregnancy and neonatal mortality, say Donghao Lu, from Karolinska Institutet in Stockholm, Sweden, and colleagues, adding that the preterm births tended to be iatrogenic rather than spontaneous events.
They write: “Although stillbirth and neonatal death are rare outcomes, the absolute risks of SGA and preterm birth are not small in pregnancies complicated with cancer.
“Careful monitoring of fetal growth and cautious decision making on the choices as well as the timing of preterm delivery should therefore be reinforced in these pregnancies.”
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