ESTROGEN-RECEPTOR STATUS OF BREAST-CANCER - A MARKER OF DIFFERENT STAGES OF TUMOR OR DIFFERENT ENTITIES OF THE DISEASE

Breast cancer can be divided into two types according to the estrogen receptor (ER) level of the tumor: ER-positive and ER-negative. Two hyp otheses have been raised about the relationship between ER-positive an d ER-negative breast tumors. One hypothesis considers ER status as an indicator of a different stage of the disease. The other regards ER-po sitive and ER-negative tumors as different entities. For both etiologi cal and biological studies of breast cancer it is important to know wh ich hypothesis is correct. In this paper, we review evidence for and a gainst each hypothesis and suggest issues to be addressed in future st udies.