anaplasia

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

(an′əplā′zhə)
n

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.