found that cytotoxic T lymphocytes (CTL) failed to kill soft tumor‐repopulating cells (TRC), while they effectively destroyed stiff differentiated TRC.[145] Mechanically, perforin needed to interact with nonmuscle myosin heavy‐chain 9, which contributed to transmit forces to F‐actins to generate enough contractile force for perforin pore formation in TRC. Here, PRF1 is linked to neoplasm.