Basal-like breast cancer, one of the most aggressive forms of breast cancer, may have different origins than scientists previously thought, a new study suggests.

This form of breast cancer accounts for about 15 percent of all breast cancers, according to a 2004 study from the journal Clinical Cancer Research. The cancer has a poor prognosis and affects mostly young and/or African American women.

The glandular tissue of the breast is made of two types of cells: outer cells (called basal cells) and inner cells (called luminal cells). Scientists had thought basal-like breast cancer originated from the basal cells.

But the cancer may instead have roots in a different type of cell called luminal intermediate cells, which line the mammary ducts, according to a study by several research institutes around the United Kingdom.

"Our results highlight luminal intermediate cells as a key to understanding the origins of basal-like breast cancer," study researcher Dr. Matthew J. Smalley, from the Breakthrough Breast Cancer Research Centre in London, said in a statement.

Researchers found that an increase in abnormal luminal intermediate cells is associated with mutations in a breast cancer susceptibility gene.

The scientists deleted a breast cancer susceptibility gene from the two types of cells in mice. They found that deletion of the gene caused tumors in all the mice, but the mice with the gene deleted from their luminal intermediate cells had tumors identical to humans with basal-like breast cancer.

The findings could help further research in treatment for basal-like breast tumors, according to the researchers.

The study was published in the Sept. 3 issue of the journal Cell Stem Cell.