This suggests that tumor cells may be able to ‘strike back' to kill those immune cells inside.39 Based on our recent work by using NK92 cell line and human tumor cells for study, we found that cell-in-cell death process of NK92 inside tumor cells was a typical caspase-3-dependent apoptosis differing from either entosis or cannibalism.6, 40 Takeuchi et al.41 also reported the apoptotic death of a cytotoxic regulatory T-cell line inside tumor cells. The gene discussed is CASP3; the disease is neoplasm.