Angiogenic activity of plasma cell CM: chick embryo CAM-sponge assay. (A) The positive control (RPMI-1640+FGF-2) and (B) the CM of an active MM patient (progression) were loaded onto gelatin sponges implanted on top of the CAM on day 8. Macroscopic appearance of the CAM on day 12: note the presence of numerous blood vessels with a “spoked wheel” pattern around both sponges, highlighted by India ink injection. (C) Histologic section of the sponge sub (B), showing a collagenous matrix pierced by winding blood vessels (arrowheads) containing circulating cells and surrounded by a dense mononuclear cell infiltrate. (D) Histologic section of a sponge loaded with negative control medium (RPMI-1640) and devoid of vessels among the trabeculae. Bar, 3 mm in (A) and (B); 90 μm in (C) and (D).