breast cancer survival

In a 2017 study, researchers investigated the effect of pregnancy on survival for women with breast cancer. The findings suggest that pregnancy is not detrimental to breast cancer survival at five years.

 

Though a diagnosis of breast cancer around the time of pregnancy is associated with poorer disease outcomes, whether pregnancy compromises a woman’s breast cancer survival is uncertain. A better understanding of the impact of pregnancy on breast cancer survival would provide patients and clinicians with the information necessary to make informed choices concerning conception, pregnancy, and breast cancer treatment.

In a 2017 Canadian study published in JAMA Oncology, researchers investigated the effect of pregnancy on survival for women with breast cancer. The medical records of women diagnosed with stage I-IV breast cancer between 20 and 45, with no previous history of cancer (except for skin cancer), and who had not undergone uterine or ovarian removal surgery were accessed from the Ontario Cancer Registry (OCR) between January 1, 2003 and December 31, 2014. Information concerning the age at diagnosis, the date of diagnosis, breast cancer stage, the presence of cancerous cells within lymph nodes, tumour type – displaying or not displaying the estrogen receptor (ER+ or ER-), progesterone receptor (PR+ or PR-), or human epidermal growth factor receptor 2 (HER2+ or HER2-), by which tumours respond to compounds which promote their growth and spread – and the receipt of chemotherapy or radiation therapy was obtained for each patient.

The date of delivery minus 9 months was considered the date of conception for live births and stillbirths. The date of eviction minus 3 months was considered the date of conception for abortions. Women were classified as having had no pregnancy (between 5 years before and 5 years after diagnosis), pregnancy before breast cancer (conceiving between 5 years and 1 year before diagnosis), pregnancy-associated breast cancer (conceiving between 11 months before diagnosis and 21 months after), or having pregnancy following breast cancer (conceiving between 22 and 60 months after diagnosis).

In total, 7,553 women were analyzed. The average age at diagnosis was 39.1 years. Of these women, 5,832 (77.2%) had no pregnancy, 1,108 (14.7%) had pregnancy before breast cancer, 501 (6.6%) had pregnancy-associated breast cancer, and 112 (1.5%) had pregnancy following breast cancer. Women with pregnancy-associated breast cancer were 6.3% more likely to have stage II-IV breast cancer, 4.4% more likely to have cancerous cells within the lymph nodes, to have ER- tumours, and to have triple negative (ER-, PR-, and HER2-) tumours than women who had had no pregnancy. A total of 975 women (12.9%) died by the end of the investigation period. The 5-year survival rate was 87.5% for women who had no pregnancy, 85.3% for women who were pregnant before breast cancer, 82.1% for women with pregnancy-associated breast cancer, and 96.7% for women who were pregnant following breast cancer. Adjusting for age at the time of diagnosis, the all-cause mortality rate was 18% higher among those with pregnancy-associated breast cancer compared to those who had had no pregnancy. Taking age, tumour size, the presence of cancerous cells in the lymph nodes, and tumour type into account, the rate was 11% higher with or without chemotherapy or radiation therapy. In women who had a live birth or stillbirth delivery, the age-adjusted rate was 42% higher and 24% higher, respectively, when the other factors were taken into account. Women with pregnancy-associated breast cancer aged 20-29 were 2.06 times as likely as those aged 40-44 and 1.71 times as likely as those aged 30-34 to die from any cause. The risk of death at 5 years post-diagnosis was 63% lower for those with ER+ tumours compared to those with ER- tumours.

Overall, the study findings suggest that pregnancy is not detrimental to breast cancer survival at 5 years. Moreover, the survival rate was higher in women who became pregnant 2-5 years after diagnosis than in non-pregnant women. It has been suggested that this may be due, in part, to the increased likelihood of choosing to conceive following a favourable prognosis. It was found that among the factors explored, pregnancy-associated breast cancer was most strongly correlated with ER- tumours. Future research will be needed in order to determine whether pregnancy increases the risk of ER- tumours, pregnancy prevents ER+ breast cancers, or whether pregnancy is associated with a switch from ER+ to ER- in tumours. Youth was also found to have a strong impact on survival. Notably, however, the likelihood of a stage II-IV tumour was higher among women with pregnancy-associated breast cancer, most of whom were under 30. The information gathered in this study was obtained from the Ontario Cancer Registry, which provided no information on hormonal treatment, or on tumour size, lymph node status, or breast cancer type prior to 2010, and as such, the contribution of these factors to the outcomes observed may not be fully represented. As the timing of conception was calculated rather than recorded, the actual times of conception may have been misrepresented and therefore some women may have been misclassified.

Youth was also found to have a strong impact on survival. Notably, however, the likelihood of a stage II-IV tumour was higher among women with pregnancy-associated breast cancer, most of whom were under 30. The information gathered in this study was obtained from the Ontario Cancer Registry, which provided no information on hormonal treatment, or on tumour size, lymph node status, or breast cancer type prior to 2010, and as such, the contribution of these factors to the outcomes observed may not be fully represented. As the timing of conception was calculated rather than recorded, the actual times of conception may have been misrepresented and therefore some women may have been misclassified.

 

Written By: Raishard Haynes, MBS



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