> ## Content Index
> Fetch the complete content index at: https://www.foodconsumer.org/llms.txt
> Use this file to discover other available public pages before exploring further.

# Tamoxifen can cause cancer in breast cancer patients
- URL: https://www.foodconsumer.org/tamoxifen_breast_cancer_1209120850/
- Published: 2012-12-09T09:49:00.000Z
- Updated: 2026-09-22T16:01:37.000Z
- Description: Wozniak and colleagues in Lodz found tamoxifen caused DNA double-strand breaks in healthy lymphocytes at both low and high doses but damaged MCF-7 breast cancer cells only at the high dose, and the healthy cells repaired that damage less completely.
- Author: Food Consumer
- Tags: Drug, Health News, #vivvo-import

By David Liu, PHD

Sunday Dec 9, 2012 (foodconsumer.org) -- Tamoxifen is a non-steroidal drug indicated to treat and prevent breast cancer often in premenopausal women who have been diagnosed with breast cancer. The drug reduces breast cancer growth by blocking estrogen receptors in breast tissue.

A study in Archives of Toxicology found that Tamoxifen can damage healthy cells more than cancer cells by generating free radicals, which cause mainly DNA strand breaks in this case, potentially increasing risk of developing other types of malignancies.

K. Wozniak at Department of Molecular Genetics, University of Lodz in Lodz, Poland and colleagues found the adverse effect when they tested the drug in both healthy human peripheral blood lymphocytes and MCF-7 breast cancer cells.

They found tamoxifen induced DNA double strand breaks in healthy lymphocytes at both low and high doses (5 and 10 microM), but only at a high concentration (10 microM) it could damage breast cancer cells, suggesting that healthy cells are more vulnerable than breast cancer cells to the damage induced by tamoxifen.

One reason for healthy lymphocytes to more easily get injured by tamoxifen is that the healthy cells could not have complete repair of the damage induced by the chemopreventative while breast cancer cells had complete repair of the DNA damage. Specifically, the researchers found the anticancer drug damges DNA by inducing oxidation of purines and pyrimidines, two of the building blocks of nucleic acids for DNA.

The researchers concluded "Our results indicate that TAM (Tamoxifen) can be genotoxic for normal and cancer cells by free radicals generation. It seems to have a higher genotoxic potential for normal cells, which can be the result of incomplete repair of DNA DSBs (double strand breaks)."

The free radicals can be neutralized by using free radicals scavengers like vitamin C. But the researchers cautioned that they can interfere with the anticancer effect of tamoxifen on breast cancer by modulatin tamoxifen-induced DNA damage.

However, G. Muralikrishnan and colleagues from University of Madras in Madras, India published a study in Chemotherapy suggesting that taking vitamin C supplements may help breast cancer patients.

Muralikrishnan et al. tested vitamin c treatment in 60 postmenopausal women with breast cancer and vitamin C significantly restored antioxidant enzymes such as catalase, superoxide dismutase (SOD), glutathione peroxidase and glutathione-S-transferase.

And they reported "co-administration of vitamin C is more beneficial in breast cancer patients treated with tamoxifen."

Although tamoxifen is intended to reduce the risk of developing breast cancer, the anticancer drug can ironically cause endometrial cancer among other risks. The American Cancer Society considers tamoxifen as a known carcinogen, which can increase risk of some types or uterne cancer.

Tamoxifen is used to prevent breast cancer, but studies have shown that tamoxifen use did not reduce death risk from breast cancer.