Folate binding protein and the estrogen receptor in breast cancer.

Folate binding protein (FBP) and estrogen receptor (ER) content were determined in primary breast cancers of 48 patients. The mean FBP level was significantly higher in ER-negative tumors than in ER-positive tumors and largely independent of the degree of tumor involvement or menopausal status. FBP correlated negatively with ER and this was most marked for tumors from postmenopausal women. Since FBP may decrease available intracellular folate the present data support clinical findings that chemotherapeutic agents may be more effective for ER negative tumors.