Approximately 75 percent of all breast cancers are estrogen receptor (ER) and/or progesterone receptor (PR) positive, and exposure to estrogen and progesterone stimulates cancer growth. In contrast, blocking the effect of estrogen on breast cancer cells has markedly improved the outcome of ER+ patients. As during pregnancy estrogen and progesterone levels increase, it has been hypothesized that breast cancer during pregnancy (BCP) carries a poor prognosis, although results from previous studies yielded conflicting results.
To investigate the prognostic impact of pregnancy on breast cancer that is detected during pregnancy, the German Breast Group (GBG) and Cancer in Pregnancy (CIP) collaborated in an observational study on all patients diagnosed with primary, non- metastatic BCP between January 1, 2000 and September 30, 2011 (n=311). A group of non-pregnant, stage I-III breast cancer patients aged ≤ 45 years served as controls (n=865). Patients were recruited in 7 countries. Between these groups, disease-free survival (DFS) and overall survival (OS) were compared after adjusting for age at diagnosis, stage, grade, tumor histology, ER, PR and human epidermal growth factor 2 receptor (HER2) status, trastuzumab use, type of chemotherapy, use of radiotherapy and endocrine therapy.
This study did not find a negative effect of patients diagnosed with BCP with regard to DFS (hazard ratio [HR] 1.34, 95% CI 0.93-1.91; P=0.14). Similar results were found for OS (HR 1.19 , 95% CI 0.73-1.93; P=0.51). The average 5 years DFS probability based on the Cox model was 65% for BCP patients compared to 71% for the matched non-pregnant patient. For average 5 years OS, the authors found 78% vs. 81%, respectively.
This observational study assessed whether being diagnosed with non-metastatic breast cancer during pregnancy negatively affects prognosis. No significant differences in DFS and OS could be demonstrated after adjusting for known confounding factors. The authors conclude that the elevated levels of hormones during pregnancy do not contribute to a more aggressive disease course. Those findings are in line with results from Schedin1 (Schedin 2006 in Nature Reviews Cancer) and Lyons2, (Lyons et al. 2009 in J Mammary Gland Biol Neoplasia) who hypothesized that the post-partum inflammatory changes and mammary gland involution contribute to early tumour cell dissemination was critical for tumorgenesis in breast cancer rather than pregnancy itself.
The findings of this observational study have an impact on the way pregnant women with breast cancer are counseled as their outcome is comparable to non-pregnant patients. It also supports the start of treatment with continuation of pregnancy.
- Schedin P. Pregnancy-associated b Pregnancy-associated breast cancer and metastasis.reast cancer and metastasis. Nat Rev Cancer. 2006 Apr;6(4):281-91.
- Lyons TR, Schedin PJ, Borges VF. Pregnancy and breast cancer: when they collide. J Mammary Gland Biol Neoplasia. 2009 Jun;14(2):87-98.
Why does pregnancy not affect the outcome in breast cancer during pregnancy?
I have no actual, potential, real or apparent interest to declare. I have no involvement that might raise the question of bias in the work reported or in the conclusions, implications, or opinions stated