Patients with ER (estrogen receptor) positive breast cancer may choose to preserve fertility using cryopreservation. The process included COS (controlled ovarian stimulation) to harvest eggs for cryopreservation. COS causes an increase in estrogen, which can prove detrimental for patients with ER positive breast cancer. Tamoxifen is a drug used to reduce the risk to breast cancer patients. Researchers from the Academic Medical Centre in Amsterdam recently published a study in the journal Human Reproduction on a possible problem with Tamoxifen concentrations.
In order for Tamoxifen to effectively prevent growth of breast cancer, endoxifen levels must reach therapeutic levels. Endoxifen is the active metabolite of Tamoxifen. Researchers tested four women undergoing COS after being diagnosed with ER positive breast cancer. All women took part in five COS cycles with egg harvest.
Conclusion: Endoxifen levels varied widely among the four women. When given 60 mg of Tamoxifen, though serum levels of endoxifen ranged from 3.96 ng/ml to 41 ng/ml. Therapeutic levels are achievable, but not in all women.
Source: Balkenende EM, Dahhan T, Linn SC, Jager NG, Beijnen JH, Goddijn M. A prospective case series of women with estrogen receptor-positive breast cancer: levels of tamoxifen metabolites in controlled ovarian stimulation with high-dose tamoxifen. Hum Reprod. 2013 Jan 18.