SNAI1 and neoplasm: Snail(+) tumor cells can secrete Human follistatin-like protein 1 (FSTL1) not only to directly promote tumor bone metastasis, but also to generate CD45(-) activated leukocyte cell adhesion molecule (ALCAM)(+) cells, which can be surrounded by CD8+ T cells with weak CTL activity that contribute to the development of bone metastatic cancer (35).