The failure of simple integrin ligation to simulate the BCG response, the ability of antibody mediated crosslinking of α5β1 integrin to duplicate the BCG response, the central role of FN in the biologic response to BCG, together with the predominance of α5β1 as the principal FN binding integrin on urothelial cells, strongly supports a model in which the biologic response of the tumor cell to BCG occurs as a consequence of BCG crosslinking of α5β1 integrin receptors. The gene discussed is FN1; the disease is neoplasm.