ESR1 and plasma cell myeloma: In tumor-induced bone resorption, the use of FXR antagonists inhibits RANKL- and tumor cell (human breast tumor cells [MDA-MB-468] or human multiple myeloma [U266]) induced osteoclast generation by inhibiting NF-κB activation.194 FXR is also expressed in MCF-7 (estrogen receptor (ER)-positive) cell lines of breast cancer origin.