RBL2 and cancer: Interestingly SLPI a serine protease inhibitor overexpressed in a wide variety of human cancers, including breast, lung, ovarian and colorectal carcinomas, and glioblastoma [44–48], is highly upregulated in RA1, RB1, RB1.1 and RB2 erlotinib-resistant cell lines (Figure 8b, 8c).