Indirect effect of cyclophosphamide on the lung tumor colony formation and on the conditioned media activity.

Mice pretreated with cyclophosphamide (CY) had more tumor colonies in lungs following i.v. injection than their intact counterparts. CY treated mice restored with spleen cells showed incomplete reduction of the artificial metastasis in lungs. Conditioned media prepared from lungs contain two factors: stimulating and inhibiting cell proliferation in vitro. Conditioned media from CY treated mice were found to have a decreased inhibitory ability.