A Colorado woman died after using cesium chloride supplements as an alternative treatment for breast cancer, a new case study reports.

The 61-year-old woman had been takingcesium supplements daily for a year as a treatment for breast cancer, but it was a single injection of cesium chloride liquid into a lump in her right breast that is likely what ultimately proved fatal, the report said.

The woman had been following the advice of a nutritionist, who had recommended cesium chloride to help shrink her breast tumor.

Cesium chloride is an alternative treatment that "supposedly increases the pH level of cancer cells to kill them, while not altering the pH of healthy cells," said study author Dr. Daniel Sessions, who was a medical toxicology fellow at the Rocky Mountain Poison and Drug Center in Denver and was involved in the case. (A cell's pH is a measure of how acidic or basic its internal environment is.)

However, this theory of how cesium chloride works "has not been scientifically proven to be true," Sessions said. [7 Medical Myths Even Doctors Believe]