SFN and breast cancer: Comparative gene expression analysis showed a specific expression of CD56 mRNA and protein only in the NK-92-sensitive (hTERT-HME1 and BT549), but not in the NK-92-resistant breast cancer cell lines (BT474, SKBR3, HCC1954, MDA-MB-231, BT20, T47D, HCC1954 and MCF-7).