A genetic test for patients with early breast cancer can identify those who will be helped by chemotherapy, and for those women the benefits far outweigh the drawbacks, researchers said on Friday.

Currently, doctors assume that all breast cancer patients will benefit similarly from chemotherapy, which has harsh side effects including nausea, infection and blood-clotting problems.

“These data advance the state of the art in cancer care and call for a reevaluation of treatment practice ... physicians can more effectively optimize a treatment plan and avoid under-treating and over-treating breast cancer patients,” study investigator Dr. Norman Wolmark said in a statement.

The test, made by Genomic Health Inc., is already used to quantify the likelihood that a patient’s breast cancer will return. Known as Oncotype DX, the panel analyzes 21 genes related to the cancer.

The new research involves breast cancer patients with estrogen-sensitive tumors whose cancer had not spread to lymph nodes and who took tamoxifen, a hormone therapy used to treat most cases of breast cancer when caught before it has spread. This group accounts for about half of all newly diagnosed breast cancer patients in the United States each year.

A study of 651 patients found that breast cancer patients shown to be at high risk of relapse who were treated with chemotherapy saw a 28-percent reduction in the chance of cancer returning in 10 years. This group represents about 25 percent of patients with node-negative, estrogen-sensitive breast cancer.

At the same time, the study found that patients identified as having a low risk of recurrence derive only minimal, if any, benefit from chemotherapy. They represent about 50 percent of these patients.

The results were presented on Friday at the San Antonio Breast Cancer Symposium by experts from the National Surgical Adjuvant Breast and Bowel Project and Genomic Health.

Other studies confirmed that Oncotype DX is better than traditional measurements, such as patient age, tumor size and tumor grade at determining the likelihood that breast cancer would return.

A study of 668 patients, published Friday in the online edition of the New England Journal of Medicine, found that about 50 percent of patients are reclassified (from low risk to higher risk, or from higher risk to low risk) by the genetic testing score when compared to classification by existing guidelines.

“We believe the Oncotype DX assay will become a standard of care in breast cancer, providing critical information to help physicians and patients make potentially life changing treatment decisions,” said Dr. Steven Shak, chief medical officer of Redwood City, California-based Genomic Health.

The World Health Organization says 1.2 million people will develop breast cancer this year and 40,000 in the United States alone will die of it.

SOURCE: New England Journal of Medicine, December 30. 2004.