be targets for future biologic-marker research. The control of growth and differentiation involves sophisticated modes of cellular communication. Figure 6-2 illustrates actual and potential modes of growth control, as might be found in the prostate. Endocrine control is exemplified by the effects of androgen, which stimulates the production of growth factors in both epithelial and stromal cells. Fibroblasts secrete factors that bind to epithelial-cell receptors.