Our previous studies had demonstrated that tumorigenic cells rather than differentiated tumor cells are selected and grow in 90 Pa soft 3D fibrin gels (Liu et al, 2012; Liu et al, 2018); and these selected cells are physically much softer than the differentiated counterparts and can be represented by CD133hi melanoma cells or ALDH+ breast cancer cells in vivo (Liu et al, 2018). The gene discussed is LDHA; the disease is breast carcinoma.