PD 0332991 and tamoxifen in a tamoxifen-insensitive cell line. PD 0332991 (PD) enhances the effects of tamoxifen (Tam) in an MCF7 tamoxifen-insensitive cell line. Dark triangles, PD 0332991 and tamoxifen combination; open squares, PD 0332991 alone; grey diamonds, tamoxifen alone; grey circles, MCF7 parental with tamoxifen alone. Error bars represent the standard error for two separate experiments. The MCF7 parental line is 100% inhibited under these conditions in the presence of tamoxifen (grey circles).