An amino acid found in some foods may make a woman’s body resistant to a widely-used  breast cancer drug.

Researchers have discovered an unexpected relationship between levels of the amino acid leucine (found in beef, chicken, pork and fish and other foods) and the development of tamoxifen resistance in estrogen-receptor positive breast cancer.

About one in eight women in the United States will develop breast cancer in her lifetime. The vast majority of these cancers rely on the hormone estrogen to grow. Estrogen-receptor positive (ER+) breast cancer tumors are frequently treated with the drug tamoxifen, which blocks the hormone’s effect on the tumor. However, many tumors eventually become resistant to tamoxifen, allowing cancer to recur or metastasize.

Now, a team of researchers at the Cancer Center at Beth Israel Deaconess Medical Center (BIDMC) has discovered an unexpected relationship between levels of the amino acid leucine and the development of tamoxifen resistance in ER+ breast cancer. 

The findings, published in the journal Nature, reveal a potential new strategy for overcoming resistance to endocrine drugs in ER+ breast cancer patients.