Dictionary:

anaplasia

  (ăn'ə-plā'zhə)

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Reversion of cells to an immature or a less differentiated form, as occurs in most malignant tumors.

A regressive change in cells toward a more primitive or embryonic cell type. Anaplasia is a prominent criterion of malignancy in tumors.

Loss of differentiation of cells, an irreversible alteration in adult cells toward more primitive (embryonic) cell types; a characteristic of tumor cells.