41.   Naturally occurring tumor cells are so deranged and vary so much from patient to patient that it is hard for scientists to understand which genetic changes are important.

42.   Next, the tumor cells switch on genes that draw blood vessels to them, supplying them with a ready source of oxygen and nutrients.

43.   Normally active killer cells would destroy roving tumor cells, but a general anesthetic suppresses them just when the patient needs them most.

44.   One could be assigned to a cancer experiment and injected with tumor cells.

45.   Onyx is also studying ways to use the virus to carry therapeutic genes to tumor cells.

46.   Perhaps the final hurdle for a successful tumor cell is to activate its telomerase gene.

47.   Probably four or five separate genes must be knocked out before a normal cell becomes a fully developed tumor cell.

48.   Removing the tumor cells reduces the chance of a recurrence of the cancer.

49.   Roth plans to use a virus to take antisense genes into the tumor cells.

50.   Siamon Gordon, a macrophage expert at Oxford University, notes that some cancers are known to subvert macrophages to protect rather than attack tumor cells.