In another case, the placental growth factor (PLGF) secreted by small-cell lung cancer (SCLC) has been shown to mediate the disassembly of brain endothelial tight-junctions and promote brain metastasis both in vitro and in patient samples, but the study lacks the in vivo data vital to drawing conclusions with respect to the PMN [75] (Figure 2). Here, PGF is linked to small cell lung carcinoma.