205P - Influence of green tea consumption on endoxifen steady-state concentration in breast cancer patients treated with tamoxifen

Background

Tamoxifen is an effective drug in the treatment of estrogen receptor positive breast cancer. Nowadays many cancer patients often use additional herbs or supplements in combination with their anti-cancer therapy. Green tea is one of the most used dietary supplements among breast cancer patients. Furthermore, several in vitro studies suggest anti-cancer effects of epigallocatechin-3-gallate (EGCG); the major catechin in green tea. The aim of this study was to investigate the influence of green tea supplements on the pharmacokinetics (PK) of endoxifen: The most important metabolite of tamoxifen.

Methods

In this singe center, randomized cross-over trial, effects of green tea capsules on endoxifen levels were evaluated. Fourteen patients treated with tamoxifen for at least 3 months (assuring steady state) received tamoxifen (20-40 mg once daily for a period of 28 days within the study) followed by the combination with green tea supplements (1 g twice daily; containing 300 mg EGCG) for 14 days (or vice versa). Blood samples (n=13/day) were collected periodically for 24 h after tamoxifen intake during hospital admission on days 14 and 42. The main PK parameters for endoxifen, area under the curve (AUC_0-24h), maximum concentration (C_max) and trough concentration (C_trough) were obtained from individual plasma concentration-time curves.

Results

A difference of -0.4% was found in geometric mean of endoxifen AUC_0-24h in the period with green tea versus tamoxifen monotherapy (95CI: -8.6 – 8.5%; p=0.916). Also, geometric mean C_max and C_trough values for endoxifen were similar with or without green tea consumption (38.5 nM; CV 37.3% vs 39.6 nM; CV 41.7% and 32.2 nM; CV 34.1% vs 31.9 nM; CV 39.8%, respectively). No statistical differences of either C_max (95CI: -10.6 – 5.6%; p=0.466) or C_trough (95CI: -7.3 – 10.5%; p=0.770) were found between the combination with green tea and tamoxifen monotherapy. Moreover, no severe toxicity was reported.

Conclusions

In conclusion, this study demonstrated the absence of a PK interaction between green tea supplements and tamoxifen. Therefore, the combination of tamoxifen and green tea is safe in patients using tamoxifen from a PK point of view.

Clinical trial identification

Netherlands Trial Register: NL8144.

Editorial acknowledgement

Legal entity responsible for the study

AHJ Mathijssen.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.