estrogen receptor–negative

Definition of estrogen receptor negative
National Cancer Institute

estrogen receptor negative

(ES-truh-jin reh-SEP-ter NEH-guh-tiv)
Describes cells that do not have a protein that binds to the hormone estrogen. Cancer cells that are estrogen receptor negative do not need estrogen to grow. This means that they will keep growing when estrogen is not present and do not stop growing when treated with substances that block estrogen from binding. Also called ER negative.

Source: NCI Dictionary of Cancer Terms