BREAST CELLS PLAY DEAD
There seems to be something fundamentally different about some of the cells in human breast tissue, Thea D. Tlsty, of the University of California, San Francisco, and colleagues report this week (Nature, Vol. 409, No. 6820, 01 Feb 2001; pp. 633-637). Most cells divide a limited number of times before stopping to enter an irreversible, non-dividing state called 'senescence'. In vitro, at least, normal human mammary epithelial cells (HMECs) - the kind of cells that line vessels and so on - do not do this, Tlsty's group have found.
Instead, HMECs go through two growth phases before eventually entering senescence. Between these spurts they languish in a growth plateau that looks deceptively like senescence but from which they emerge to carry on doubling, accruing chromosomal abnormalities as they go. This suggests that pre-cancerous transformations are much more likely to occur in mammary epithelial tissue than elsewhere in the breast - a prediction consistent with epidemiological data. "Growth past senescent barriers may be a pivotal event in the earliest steps of carcinogenesis," the team concludes.
Thea D. Tlsty
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