Researchers at New York-Presbyterian Hospital and Weill Cornell Medical Center have created a test that could help doctors identify which breast cancer patients need aggressive therapy. The study, published in the online version of Clinical Cancer Research, could prevent many women from undergoing unnecessary chemotherapy or radiation treatment. The test was developed based on research by scientists at Albert Einstein College of Medicine at Yeshiva University, who recently found that the interactions between three cell types could predict whether a patient’s localized breast cancer would spread throughout the body. The combined presence of these three cells constituted a “tumor microenvironment of metastasis,” or TMEM. Researchers at New York Presbyterian and Weill Cornell then developed a test to determine the density of TMEMs. The more TMEMs in a tissue sample, the more likely the tumor was to metastasize. By determining a woman’s risk of metastasis, the test could prevent many women from undergoing unnecessary chemotherapy or radiation treatment. Breast cancer spreads in only about 40 percent of patients with higher-grade tumors. Many women needlessly undergo harsh cancer treatments that cause severe side effects and sometimes worsen the disease. The researchers are now working on a test that could theoretically predict metastatic breast cancer before a tumor forms.