Are phytoestrogens contraindicated in a woman with previous breast cancer?/nA woman previously trea

Fråga: Are phytoestrogens contraindicated in a woman with previous breast cancer? A woman previously treated for breast cancer wants to take phytoestrogens for climacteric symptoms.

Sammanfattning: Phytoestrogens affect the estrogenic system in a complex manner and appear to possess both estrogenic and anti-estrogenic properties. There are some indications that phytoestrogens may protect against breast cancer, allegedly by antagonising the effects of endogenous estrogen. It is not known whether this applies to post-menopausal women, where the pro-estrogenic effects of phytoestrogen may be predominant. Indeed, phytoestrogens have been shown to stimulate growth of breast cancer cells in vitro. Finally, the documentation supporting use of phytoestrogens for post-menopausal symptoms is scarce, and the only study addressing use in breast cancer survivors failed to show a pharmacological effect on estrogen deficiency symptoms.

Since available data regarding safety and effectiveness is insufficient, we advice against use of phytoestrogens in women previously treated for breast cancer.

Svar: Phytoestrogens are a diverse group of non-steroidal plant derived compounds possessing estrogenic activity (1). Examples of dietary phytoestrogen sources are soybean, red clover, different fruits, green tea and alfalfa. The estrogenic properties of phytoestrogens are not fully understood, but are thought to derive from actions on estrogen receptors, interactions with key enzymes in sex steroid production and stimulation of production of sex hormone binding globulin (SHBG).

The effects of phytoestrogens on estrogen receptors (ER), being partial agonists, are both agonistic and antagonistic, depending on phytoestrogen concentration and presence of endogenous estrogen (1). In vitro, different phytoestrogens have been shown to stimulate growth of estrogen-dependent breast cancer cells (2). On the other hand, a few studies indicate a protective effect of high dietary phytoestrogen intake against breast cancer (3-4). This could be due to an antiestrogenic net effect of phytoestrogens in presence of endogenous estrogen. Specific data concerning postmenopausal women is missing.

The receptor actions of phytoestrogens are partially selective for the beta subtype of the estrogen receptors, whereas endogenous estrogen acts on both alpha and beta estrogen receptors (1).This difference has attracted much attention in the field of prostatic cancer research, since the prostate estrogen receptors population is predominantly of the beta class. However, the mammary gland contains equal amounts of the two receptor subtypes, and the phytoestrogens´ subtype specificity offers no obvious advantages here (5).

Lastly, the use of phytoestrogens in the treatment of climacteric symptoms is not well documented and even less so in breast cancer patients (6). One single study was found, investigating the effect of 150 mg phytoestrogen (isoflavones) per day on hot flashes in women previously treated for breast cancer (6). This double-blind, placebo-controlled cross-over study in 177 women failed to show any therapeutic effect of four weeks´ treatment.