"As it happens with cancer research, we are finding that the subtype of triple-negative breast cancer (TNBCs, essentially those cancers that cannot be treated with HER2-targeted and hormone therapies), contain many subsets themselves.
This theory may explain why any one drug class or approach to treatment has not been very successful--a topic that was addressed during the annual meeting of the American Association for Cancer Research.
To date, TNBC has become a catch-all disease with any breast cancer that isn't HER2-positive or ER-positive. Right now, the term triple-negative breast cancer is merely a "descriptive and operational term," as William Foulkes, the director of the cancer genetic program at Quebec's McGill University, put it. It doesn't have a biological definition. And its importance has risen only in the past five years."