Effects of the placenta on metastatic breast cancer

Cancer and pregnancy coincide relatively rarely, approximately 1 in 1,000 pregnancies [1,2]. However, the current trend of delaying pregnancy, accompanied by age-related increases in the incidence of many malignancies is expected to increase the incidence of pregnancy-associated cancer [1]. The most common malignancies associated with pregnancy are breast (PABC), cervical cancer, melanoma, and hematological cancers (Table 1) [3–5]. Most malignancies diagnosed during pregnancy and/or lactation do not carry an increased risk of mortality, except for patients diagnosed with PABC or with ovarian cancer during lactation [3]. Women with PABC have a 2.5-fold higher likelihood of being diagnosed with metastatic disease than do nonpregnant women [6]. Furthermore, PABC biopsy specimens exhibit poor histologic and prognostic features [1]. These histological parameters do not differ significantly from those of age-matched, nonpregnant women with breast cancer [6], nevertheless, a higher incidence of estrogen receptor (ER) -negative cancer is observed in pregnant compared to nonpregnant women [7].