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Anaplasia (from Ancient Greek ἀνά (ana) 'backward' and πλάσις (plasis) 'formation') is a condition ofcells with poorcellular differentiation, losing themorphological characteristics of mature cells and their orientation with respect to each other and toendothelial cells. The term also refers to a group of morphological changes in a cell (nuclearpleomorphism, alterednuclear-cytoplasmic ratio, presence ofnucleoli, high proliferation index) that point to a possiblemalignant transformation.[1]
Such loss of structural differentiation is especially seen in most, but not all, malignantneoplasms.[2] Sometimes, the term also includes an increased capacity formultiplication.[3] Lack of differentiation is considered a hallmark of aggressive malignancies (for example, it differentiatesleiomyosarcomas fromleiomyomas). The termanaplasia literally means "to form backward". It implies dedifferentiation, or loss of structural and functional differentiation of normal cells. It is now known, however, that at least some cancers arise fromstem cells intissues; in these tumors failure of differentiation, rather than dedifferentiation of specialized cells, account for undifferentiatedtumors.
Anaplastic cells display markedpleomorphism (variability). Thenuclei are characteristically extremely hyperchromatic (darkly stained) and large. Thenuclear-cytoplasmic ratio may approach 1:1 instead of the normal 1:4 or 1:6. Giant cells that are considerably larger than their neighbors may be formed and possess either one enormousnucleus or several nuclei (syncytia). Anaplastic nuclei are variable and bizarre in size and shape. Thechromatin is coarse and clumped, andnucleoli may be of astounding size. More important,mitoses are often numerous and distinctly atypical; anarchic multiple spindles may be seen and sometimes appear as tripolar or quadripolar forms. Also, anaplastic cells usually fail to develop recognizable patterns of orientation to one another (i.e., they lose normal polarity). They may grow in sheets, with total loss of communal structures, such asgland formation or stratifiedsquamous architecture. Anaplasia is the most extreme disturbance in cell growth encountered in the spectrum of cellular proliferations.[4]
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