New personalized therapy boosts tamoxifen effectiveness in breast cancer patients

Breast cancer is the most common cancer among women worldwide (WHO, 2023). The Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology (IKP) has now developed a new therapy in a clinical study that tailors hormone treatment for breast cancer to the individual patient. The aim is to improve the effectiveness of tamoxifen – a drug that has been used for decades to treat hormone-dependent breast cancer – in patients for whom the drug has not previously been as effective as desired.

Tamoxifen inhibits the growth of hormone-sensitive breast cancer cells by preventing the hormone estrogen from binding to its receptor in the tumor cells. However, for the drug to work optimally, it must be converted into its active form, (Z)-endoxifen, in the body. In about one-third of patients, this metabolic process is limited by the enzyme CYP2D6. This variability is genetically determined and can contribute to an increased risk of recurrence in breast cancer patients.

TAMENDOX addresses this issue: It specifically supplements (Z)-endoxifen to compensate for the insufficient conversion of tamoxifen and make the therapy more effective.

Under the direction of the IKP and in collaboration with 38 clinics in Germany, 235 patients with hormone receptor-positive, i.e., hormone-dependent breast cancer in the early stages were treated as part of a multicenter study. Depending on their individual genetic profile or drug levels in the blood, the patients received either tamoxifen alone (monotherapy) or in combination with (Z)-endoxifen over a period of six weeks. The results showed that breast cancer patients receiving combination therapy achieved the desired drug concentration in the blood, similar to that found in patients receiving tamoxifen monotherapy and with normal metabolism.

With TAMENDOX, we are offering the first effective solution to a long-standing problem: the insufficient effect of tamoxifen in a significant proportion of patients. The results impressively demonstrate how targeted personalized medicine can significantly improve the effectiveness of existing therapies – directly benefiting patients."

Dr. Matthias Schwab, head of the Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, Bosch Health Campus

The new treatment method was very well tolerated by the patients. Side effects were mild and occurred at the same rate as in the group receiving tamoxifen monotherapy.

Premenopausal women in particular could benefit from this new personalized therapeutic approach, as alternative therapies, such as the use of aromatase inhibitors, are limited for them. The IKP is currently working on a concept for drug approval for TAMENDOX in order to expand the existing range of therapies for breast cancer.