FRIDAY, Feb. 27 (HealthDay News) -- A new genetic test that analyzes a set of 50 genes to identify four types of breast cancer could lead to quicker, more immediate treatment for patients, according to U.S. researchers who developed the test.

"Unlike a widely used genomic test that applies only to lymph-node-negative, estrogen-receptor-positive breast cancer, this new genomic test is broadly applicable for all women diagnosed with breast cancer," Dr. Matthew Ellis, of the Siteman Cancer Center at Washington University in St. Louis and Barnes-Jewish Hospital and a breast cancer specialist, said in a university news release.

Ellis and his colleagues analyzed the gene activity of more than 1,000 breast tumors and identified 50 genes that could be used to identify each of the four types of breast tumors -- luminal A, luminal B, HER2-enriched and basal-like. A genetic test called OncotypeDx, which is currently in wide use, doesn't identify all four tumor types, according to background information in the news release.

"Our test is the first to incorporate a molecular profile for the basal-like type breast cancers," Ellis said. "That's important because these breast cancers are arguably the most aggressive yet the most sensitive to chemotherapy. By identifying them, we can ensure they are treated adequately."

The new test also identifies what's often considered a fifth breast cancer type, known as normal-like. But the researchers discovered that, instead of being a fifth type of breast cancer, normal-like is an indicator that a breast tumor sample contains insufficient tumor cells to make a molecular diagnosis and that a new sample needs to be taken.

The researchers also said that the 50-gene test was highly accurate in predicting how 133 breast cancer patients would respond to chemotherapy. Luminal A was not sensitive to chemotherapy, which suggests that women with this good-prognosis type of breast cancer can forgo chemotherapy in favor of hormone-based therapy, they said. Among poor-prognosis types of breast cancer, they found that basal-like was the most sensitive to chemotherapy and luminal B the least sensitive.

The study was published online Feb. 9 in the Journal of Clinical Oncology.

More information

The American Cancer Society has more about breast cancer.