Immunohistochemistry Tests Distinguish Breast Cancer Subtypes

No simple immunohistochemical test has been available to distinguish luminal A from B, which are the most common of five breast cancer subtypes defined by gene expression profiling. Luminal B is characterized by more proliferating cells and worse patient prognoses.

In the current study, Torsten O. Nielsen, M.D., Ph.D., of the University of British Columbia in Vancouver, and colleagues subtyped 357 breast tumors by gene expression profiling and tested them for Ki67 expression by immunohistochemistry to determine a cut point that distinguished between luminal A and B tumors. They then examined 2,847 independent breast tumors with four immunohistochemical tests, including estrogen and progesterone receptor expression, Ki67 expression, and HER2 status.

The researchers found that Ki67 was expressed in 13 percent or less of the cells in luminal A tumors. Using that cut point for Ki67 expression, the four immunohistochemistry tests could distinguish between luminal A and luminal B subtypes in the independent series of breast cancers.

"Although we consider breast cancer molecular subtyping by gene expression profiling to be the gold standard, we nevertheless believe that there is an immediate need for well-defined and validated immunopanels for worldwide clinical diagnostic use," the authors conclude.

This research was published in the Journal of the National Cancer Institute May 12, 2009.