The loss of specialized characteristics or function in cells or tissues, often resulting in a more primitive or basic state.
From de- (reversal) + differentiation. Latin 'differentia' (difference) combined with the suffix -ation. First widely used in biology during the 1800s-1900s to describe cellular regression.
This is exactly what happens in cancer—cells that were supposed to be, say, stomach lining cells forget their specialty and start acting like primitive cells again, multiplying wildly. It's the opposite of what should happen as organisms grow.
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