Health Care Professional Information

Common Name

Genistein Combined Polysaccharide

Brand Name


Clinical Summary

A nutritional supplement prepared by fermenting soy extract with basidiomycetes, genistein combined polysaccharide (GCP) is composed of genistein, a soy isoflavone, and polysaccharides obtained from a variety of mushrooms. Isoflavones have been shown to influence hormone-dependent cancers due to their estrogenic activity. Basidiomycetes express immune-stimulant (1) and antitumor (2) (3) activity in vitro. In prostate cancer cells, GCP was found to reduce androgen receptor and prostate specific antigen levels, induce cell growth arrest, and modestly increase apoptosis (4). GCP was also found to inhibit cell growth and induce apoptosis in androgen-dependent and -independent human prostate cancer cell lines (5). It potentiated the cytostatic and cytotoxic activities of docetaxel, bicalutamide, and the sRC kinase inhibitor, pp2 (5). Another study found that GCP treatment resulted in significant inhibition of cell proliferation and arrested the cell cycle in the G2/M phase in three human lymphoid cell lines (6).
Case reports show complete regression of T3 prostate cancer following treatment with GCP (7); and supplementation with GCP prevented recurrence of transitional cell carcinoma (TCC) of the bladder (10). However, no large scale clinical trials have been performed to verify GCP's anticancer potential.

Purported Uses
  • Cancer prevention
  • Prostate cancer
  • Genistein
  • Basidiomycetes polysaccharides
Mechanism of Action

In vitro experiments show that genistein inhibits tyrosine-specific protein kinase activity of EGF receptors. Inhibition is competitive with respect to ATP and noncompetitive to a phosphate acceptor, histone H2B. Genistein bears no structural relationship with ATP, so inhibition may not be due to true competition for the same active site as that utilized by ATP (8). Basidiomycetes polysaccharides possess antitumor, antiviral, antibacterial and immune-modulating activities. The fermentation of soy extract with basidiomycetes deglycosylates the soy isoflavones which renders them in a highly absorbable form (7). In prostate cancer cells, GCP was found to inhibit mammalian target of rapamycin (MTOR) activity (4). MTOR is a downstream effector of Akt, an enzyme which plays an important role in cancer cell proliferation and survival (4). (For more information on the mechanism of genistein action, see our monograph on soy.)


Natural isoflavones are glycosylated and poorly absorbed. Fermentation of soy extract deglycosylates the isoflavones which are absorbed more readily.

Herb-Drug Interactions

Tamoxifen: Animal studies suggest that genistein, a soy isoflavone, may antagonize the effects of tamoxifen on estrogen-dependent breast cancer.

Dosage (Inside MSKCC Only)
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  1. Rice L, et al. Mechanisms of the growth inhibitory effects of the isoflavonoid biochanin A on LNCaP cells and xenografts. Prostate 2002;52:201-12.
  2. Mentor-Marcel R, et al. Genistein in the diet reduces the incidence of poorly differentiated prostatic adenocarcinoma in transgenic mice (TRAMP). Cancer Res 2001;61:6777-82.
  3. Yuan L, Wagatsuma C, Sun B, Kim JH, Surh YJ. The role of beta-glucuronidase in induction of apoptosis by genistein combined polysaccharide (GCP) in xenogeneic mice bearing human mammary cancer cells. Ann N Y Acad Sci. 2003 Dec;1010:347-9.
  4. Vinall RL, Hwa K, Ghosh P, Pan CX, Lara PN Jr, de Vere White RW. Combination treatment of prostate cancer cell lines with bioactive soy isoflavones and perifosine causes increased growth arrest and/or apoptosis. Clin Cancer Res. 2007 Oct 15;13(20):6204-16.
  5. Burich RA, Holland WS, Vinall RL, et al. Genistein combined polysaccharide enhances activity of docetaxel, bicalutamide and Src kinase inhibition in androgen-dependent and independent prostate cancer cell lines. BJU Int. 2008 Nov;102(10):1458-66.
  6. McCall JL, Burich RA, Mack PC. GCP, a genistein-rich compound, inhibits proliferation and induces apoptosis in lymphoma cell lines. Leuk Res. 2010. Jan;34(1):69-76.
  7. Ghafar MA, et al. Regression of prostate cancer following administration of Genistein Combined Polysaccharide (GCP), a nutritional supplement: a case report. J Altern Complement Med 2002;8:493-7.
  8. Akiyama T, et al. Genistein, a specific inhibitor of tyrosine-specific protein kinases. J Biol Chem 1987;262:5592-5.
  9. Ju YH, et al. Dietary genistein negates the inhibitory effects of tamoxifen on growth of estrogen-dependent human breast cancer (MCF-7) cells implanted in athymic mice. Can Res 2002;62:2474-7.
  10. Capodice JL, Cammack AS, McKiernan JM, Katz AE. Two case reports on the use of genistein combined polysaccharide (GCP) against bladder cancer recurrence.J Complement Integr Med. 2011 Jan;8(1).

Consumer Information

How It Works

Bottom Line: There are no clinical data to support use of GCP for cancer prevention or treatment.

Genistein Combined Polysaccharide (GCP) is composed of genistein, a soy isoflavone, and polysaccharides derived from Basidiomycetes mushrooms. Although GCP itself has not been studied in the laboratory, genistein and Basidiomycetes mushrooms have, with the following results.
Genistein has been studied extensively in laboratory experiments. These generally show that genistein, when directly applied to several types of cancer cells (including estrogen receptor (ER+) and (ER-) breast cancer, prostate cancer, neuroblastoma and sarcoma), inhibits their growth and replication. Genistein 1) competes with the body's own estrogen and 2) inhibits the ability of a growth factor called EGF to stimulate its receptor and cause downstream cellular effects. Estrogen and EGF can enhance the growth of certain tumors (such as ER+ breast cancer), so scientists think that genistein might act against them to slow tumor growth. This theory has not been confirmed in humans through clinical studies, however.
Laboratory research has suggested that the polysaccharides in Basidiomycetes mushrooms can slow the growth of tumors, enhance certain activities of immune cells, and kill some bacteria and viruses on contact. It is not clear to what extent these effects occur in the human body.

Purported Uses
  • To prevent and treat cancer
    Genistein shows anti-tumor activity in the laboratory setting, but the same has not been shown for GCP.
  • To treat prostate and bladder cancer
    Case reports show benefit of GCP, but clinical trials are lacking.
Patient Warnings
  • It is controversial whether patients with estrogen-dependent tumors should take soy products such as genistein, due to its possible estrogenic activity. Patients should ask their doctors.
Do Not Take If
  • You are undergoing chemotherapy with tamoxifen (Studies in animals suggest that genistein may lessen its effects).
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