Atrimustine (Bestrabucil) is a conjugate of chlorambucil and β-estradiol benzoate. Which has high affinity for tumor cells and enhances the antitumor activity of chlorambucil[1]. At Atrimustine concentrations of 100 nM-10 μM, concentration-dependent inhibition of growth factor production by SC-115 cells can be demonstrated by 3H-thymidine uptake assay[2]. The effect of Atrimustine (Bestrabucil), a benzoate of an estradiol-chlorambucil conjugate, is examined on the production of growth factor(s) by Shionogi carcinoma 115 (SC-115) cells, an androgen-responsive cultured cancer cell line.