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What is Anaplasia is a hallmark feature of  _________. and explain in detail?
Anaplastic cells often display the following morphologic features:

Pleomorphism (i.e. variation in size and shape).
Nuclear abnormalities, consisting of extreme hyperchromatism (dark-staining), variation in nuclear size and shape, or unusually prominent single or multiple nucleoli. Enlargement of nuclei may result in an increased nuclear-to-cytoplasmic ratio that approaches 1:1 instead of the normal 1:4 or 1:6. Nucleoli may attain astounding sizes, sometimes approaching the diameter of normal lymphocytes.
Tumor giant cells may be formed. 
Atypical mitoses, which may be numerous. Anarchic multiple spindles may produce tripolar or quadripolar mitotic figures. 
Loss of polarity.

​Reference-Robbins BASIC PATHOLOGY 10th edition pg-193