Cellular basis of tumour growth

Three factors determine the growth rate of a tumour:

♦ The average cell cycle times. Values for human tumour cells usually range from 1-5 days.

♦ The growth fraction i.e. the proportion of tumour cells that are proliferating. Out-of-cycle cells are common in tumours, leading to growth fractions that are often less than 50%.

♦ Cell loss. The rate of loss of cells from tumours can be very high, often reaching 90% of cell production, and this is the principal reason why the volume doubling time is so much longer than the average cell cycle time. Cell loss occurs mainly by cell death, either as necrosis or apoptosis. Exfoliation and metastasis are other modes of cell loss.

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