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Pregnancy does not adversely affect survival among women with breast cancer
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Pregnancy did not negatively affect survival among women with breast cancer, according to results of a population-based cohort study.
Researchers reported a higher 5-year OS rate among women who became pregnant 6 months or more after breast cancer diagnosis than among women who did not become pregnant.
“We were surprised that pregnancy after breast cancer seemed to reduce the risk of the cancer coming back,” Steven A. Narod, MD, FRCPC, senior scientist at Women’s College Research Institute at University of Toronto, told HemOnc Today. “However, we need to confirm this.”
About 247,000 women in the United States were diagnosed with breast cancer last year. Women younger than 45 years accounted for 26,392 (10.7%) of these cases.
Given the trend of women delaying motherhood, the proportion women who develop breast cancer while pregnant is increasing. However, chemotherapy is not recommended during the first trimester in order to maintain the health of the mother and fetus. Radiotherapy and hormonal therapies are not recommended at any time during pregnancy.
Narod and colleagues used the Ontario Cancer Registry to identify 7,553 women aged 20 to 45 years (median age, 40 years) diagnosed with invasive breast cancer from 2003 to 2014. Researchers compared OS between women diagnosed during pregnancy or in the postpartum period with those who did not become pregnant.
More than three-quarters of women (77.2%; n = 5,832) had no pregnancy, meaning they did not conceive a child from 5 years before to 5 years after diagnosis; 14.7% had pregnancy before breast cancer (conception from 5 years to 1 year before diagnosis; n = 1,108); 6.6% had pregnancy-associated breast cancer (conception from 11 months before until 21 months after diagnosis; n = 501); and 1.5% had pregnancy following breast cancer (conception from 22 to 60 months after diagnosis; n = 112).
Five-year OS served as the primary endpoint.
Median follow-up was 5 years.
Researchers reported a higher 5-year actuarial survival rate among women who had pregnancy 6 months or more after diagnosis of breast cancer than women with no pregnancy (96.7% vs. 87.5%; age-adjusted HR = 0.22; 95% CI, 0.1-0.49).
“The apparent survival benefit in women with pregnancy following breast cancer 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,” Narod and colleagues wrote.
Narod and colleagues reported 5-year actuarial survival rates of 85.3% (age-adjusted HR = 1.03; 95% CI, 0.85-1.27) among women who conceived from 5 years to 1 year before diagnosis, and 82.1% among women with pregnancy-associated breast cancer (age-adjusted HR = 1.18; 95% CI, 0.91-1.53.
Of the women who had pregnancy before cancer and the women who had pregnancy-associated breast cancer, those aged 20 to 29 years had a significantly higher risk for death (HR = 2.04) than those aged 30 to 34 years (HR = 1.74) and those aged 35 to 39 years (HR = 1.25).
“We demonstrated a strong effect of age on survival in all hazard estimates, and young women do relatively badly,” Narod said. “About 20% to 25% of the cases end with the mother, unfortunately, dying of her cancer and leaving their children without a mother.”
Narod and colleagues acknowledged limitations to their study, including their calculation of approximate conception dates and their inability to obtain information on the use of hormonal treatment. Also, the Ontario Cancer Registry does not include information on tumor size, nodal status, ER or PR status, and ERBB2/HER-2 status for cases diagnosed before 2010.
“Many [other studies] have proposed that pregnancy may adversely affect survival in women with breast cancer when the two conditions occur together. Our study questions this position,” Narod and colleagues wrote. “We ... found that a pregnancy simultaneous with breast cancer was not detrimental to survival.” – by Chuck Gormley
For more information:
Steven A. Narod, MD, FRCPC, can be reached at Women’s College Research Institute, Women’s College Hospital, 76 Grenville St., Toronto, ON M5S 1B2, Canada; email: steven.narod@wchospital.ca.
Disclosure: Narod reports holding a Canada Research chair in Breast Cancer. The other researchers report no relevant financial disclosures.
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Richard J. Bleicher
Investigators in this large observational study reviewed more than 7,500 patient records from Ontario to evaluate the effect on timing of pregnancy relative to breast cancer development and survival. Researchers divided patients into those who did not conceive within 5 years before or after their diagnosis, those who conceived between 5 years and 1 year before their diagnosis, those who conceived between 11 months before and 21 months after their diagnosis, and those who conceived 22 months to 5 years after their diagnosis. The subgroupings were arbitrary but valuable in attempting to determine the impact of pregnancy on outcome when a woman develops breast cancer.
The challenge with performing a study like this is that breast cancer can have a “silent interval,” during which the cancer is growing but not detectable, and this silent interval can last years. We also know breast cancers can grow at different rates. Those who had pregnancy “before breast cancer” may have had their breast cancers during pregnancy, but the cancers remained undetected for a long time because they simply were less aggressive and grew slower.
If that is true, we may be seeing two different sets of pregnancy-associated breast cancers: those that were present during pregnancy but grew slowly and were detected long after pregnancy (“pregnancy before breast cancer”) and, thus, had a better prognosis, and those that grew quickly during pregnancy and had a worse prognosis (“pregnancy-associated breast cancer”).
Moreover, it remains unclear what the characteristic differences were between those who had detection during or around pregnancy vs. those who had pregnancy before breast cancer for 7 out of the 12 years of the study. This limits the power of the study.
Some of these data become very important for helping to determine the prognosis of such tumors, independent of their association with pregnancy. We also don’t know how these various cancers were detected. So screen-detected cancers — that is, mammographically detected — tend to be smaller and less aggressive than those detected by examination or those that become symptomatic. Those associated with pregnancy are not going to be screen detected during pregnancy. One would assume that those detected during pregnancy were symptomatic — as screening is not done during pregnancy — whereas those found after pregnancy were screen detected and less aggressive. We also have no data on breast feeding in these women and the ability of engorged breasts to obscure screen detection, similar to how pregnancy-associated changes can obscure detection of masses.
The study does point out the important finding of the significance of young age in how aggressive a cancer can be. This is well documented and replicated here. The study is valuable, but it also shows us that our knowledge about the association between pregnancy and breast cancer outcome is quite limited.
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