A method for prognosticating the effectiveness of a chemotherapy using monoclonal antibodies and ligand molecules. The putative anti-cancer agent has binding specificity for a oncogenic receptor molecule on the membrane of a cancer cell, such as HER-2/neu. When the putative agent binds to the oncogenic receptor, the receptor translocates from the membrane to the cytoplasm or perinucleus of the cancer cell, accompanied by a transient increase in the total cellular content of the receptor, and results in terminal cell differentiation. The efficacy of the agent in vivo can be determined in vitro by treatment of biopsied cancer cells with the agent and subsequent examination of the cells for evidence of terminal cell differentiation. Such evidence includes morphological change, reduction in cell growth, or production of chemicals associated with the mature phenotype. Additionally, treated cells may be examined with immunohistochemicals specific for the oncogenic receptor, to determine translocation of the receptor from the membrane to the cytoplasm or perinucleus. Quantification of receptor levels in treated cells by measuring optical densities after staining can be used to determine translocation, as well as a transient increase in total cellular content of the receptor.