Mayo Clinic researchers have discovered that a chemical known as endoxifen appears to be the primary metabolite responsible for the effectiveness of tamoxifen in treating breast cancer, and that it works against cancer in an entirely unexpected way.
Their study, presented at the 31st annual San Antonio Breast Cancer Symposium, finds that, in contrast to the other tamoxifen metabolites, endoxifen degrades the estrogen receptor, and thereby inhibits the growth of breast cancer cells. These new findings are believed to be the most definite laboratory analysis yet on how tamoxifen and its two main metabolites — endoxifen and 4HT (4-hydroxytamoxifen) — act against breast cancer.
“Tens of thousands of women in this country are prescribed tamoxifen for either treatment or prevention of breast cancer, and while it has shown remarkable success, it does not work for a substantial number of patients,” says the study’s lead investigator, John Hawse, Ph.D. “These findings increase our understanding of tamoxifen and, we hope, could pave the way for improved therapies.”
Tamoxifen is designed to treat estrogen-receptor positive breast cancer (70-80 percent of all breast cancer) because this receptor fuels the cancer’s growth. But tamoxifen is a “pro-drug,” which means that it is relatively inactive until converted into active “metabolites” — the 4HT and endoxifen chemicals that actually perform the work of the drug.
To read more on the study, click here.
Below is a link to an edited youtube video with Dr. Spelsberg talking about the study.
I AM 86 YEARS OLD…AM HESITANT ABOUT TAKING TOMOXIFEN BECAUSE OF ALL THE POSSIBLE SIDE EFFECTS. I AM HIGH RISK HAD A MASSIDECTOMY AND 7 WEEKS OF RADIATION..BUT STILL, I AM NOT FULLY SURE THAT TOMOXIFEN AT MY AGE SHOULD BE TAKEN..I AM HAVEING DEPRESSION,ACHES IN MY LEGS,,,GET VERY IRRITABLE…I DID STOP TAKING IT FOR 2 WEEKS AND GOT SO MUCH MORE ENERGY AND FELT SO MUCH BETTER…BUT I HAVE A FEAR ALSO…WHAT TO DO?
PLEASE REPLY.AM WAITING…
Rosalia, thank you for your comment. Unfortunately, we cannot diagnose conditions, provide second opinions or make specific treatment recommendations through this correspondence. If you would like to seek help from Mayo Clinic, please call one of our appointment offices. The numbers can be found at http://www.mayoclinic.org/ under “request an appointment.”
Rosalia, One of our physicians, Dr. Sandhya Pruthi did review your comment and has this reply:
You have had appropriate surgical and radiation treatment for your breast cancer. Tamoxifen is used to prevent the cancer from recurring. However, we always need to weigh the risks and benefits of the medication, take into account your medical history, age and type of cancer when determining if tamoxifen is necessary. It is important for you to discuss your concerns with your physician and because you are not tolerating the tamoxifen it may be necessary to stop the medication or try another medication such as an aromatase inhibitor. Your oncologist should be able to help you decide if another medication is better suited for you given your history. As I do not have information about your breast cancer pathology and medical history I am not able to comment further and this is why it best to follow up with your oncologist.