Parviz M Pour
According to a generally accepted theory development of a tumor is the results of an arrest or blockage in the differential pathway of a given cell. Most neoplasms have a reasonably constant, exponential growth rate throughout the majority of their life span. This is an important biological feature in neoplasia because it predicts the length of time required for a single neoplastic cell to reach a mass of 1 cm in diameter. This is approximately 30 population doublings and is three times longer than the length of time required to grow from 1 cm to a near lethal 1 kg mass (which requires only an additional 10 population doublings). Thus, about 75% of the life span of (untreated) neoplasms occurs prior to development of symptoms, since small tumors are generally clinically silent. It is especially sobering to note that, on average, carcinomas require a metastatic phenotype (or characteristics) between the 8th and 12th population doubling.
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