anaplasia

from The American Heritage® Dictionary of the English Language, 5th Edition.

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

from The Century Dictionary.

• noun In pathology, the sum of the morphological, structural, chemical, and other alterations which cells undergo when assuming the characteristics of malignancy.
• noun Same as anaplasis.

from the GNU version of the Collaborative International Dictionary of English.

• noun loss of structural differentiation within a cell or group of cells often with increased capacity for multiplication, as in a malignant tumor.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun biology A reversion of differentiation in cells that is characteristic of malignancy in tumours

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun loss of structural differentiation within a cell or group of cells often with increased capacity for multiplication, as in a malignant tumor