Tumor cells are capable of attracting human MSCs in vitro . Tumor CM ((D)MEM + 1% FBS) was placed in the lower chamber of a transwell migration system, while MSCs were seeded in the upper chamber. Twenty-four hours later, the number of migrating MSCs was evaluated. (a) H & E staining of the cells migrating toward CM from the indicated tumor cell lines. Migration toward (D)MEM + 1% FBS was used as baseline control. (b) Slides were scanned and the number of migrating cells in eight (1,600 x 1,000 mcM2) fields was counted. Data are presented as mean ± S.D, n = 8. P value * <0.05, ** <0.005, *** <0.0005. CM, conditioned media; MSCs, mesenchymal stem cells.