PGR and Pleural effusion: BT-20 (ER-/PR-) cells derived from a primary tumor20 was located in the lower left hand quadrant, MCF-7 (ER+/PR+) cells from a metastatic tumor with a weakly invasive ability was in the lower right hand quadrant, highly invasive MDA-MB-231 (ER-/PR-) cells21, 22 and MDA-MB-157 (ER-/PR-) cells23 derived from metastatic pleural effusions of human breast carcinoma were found in the upper left hand quadrant, and MDA-MB-361 (ER+/PR+) cells from a brain metastasis with weakly luminal epithelial-like phenotype24 were found in the upper right hand quadrant.