Breast cancer is divided into different categories, called “subtypes”. These subtypes are based on proteins that are present or missing in a patient’s tumor cells that signal them to grow in response to hormones or other factors. This is important because the cancer therapy most likely to be successful is chosen based on the patient’s cancer subtype. Although some subtypes respond to certain drugs, approximately 10 – 20% fall into the “triple-negative” breast cancer (TNBC) subtype, which is one of the most aggressive types of breast cancer. It is difficult to treat and often comes back, even when the initial therapy appears to be effective. This is why we urgently need new ways to treat TNBC. Research findings show that certain signaling proteins, kinases and phosphatases, are often changed in TNBCs. They control cell growth, response to drugs, and cell death. Drugs that target kinases have shown great success in cancer therapy. However, tumors often adapt to them, and these therapies stop working. Using combinations of drugs can overcome this, but it is hard to predict which drugs will work best together. Although kinases have been studied in great detail, less is known about phosphatases and their function as tumors adapt to therapy might help us to better treat TNBC. We have developed a new approach to study phosphatases in tumors and cancer cells. Our analyses will help to determine their role in TNBC, identify new targets for drug development, and improve predictions for combination drug therapies.