anaplasia
Summary
Anaplasia refers to the loss of cellular differentiation, a hallmark feature of malignant neoplasms. Anaplastic cells lack normal structure and function, resembling primitive or undifferentiated cells. This feature is associated with aggressive tumor behavior and poor prognosis.
Detail
Anaplasia is characterized histologically by pleomorphism (variation in cell size and shape), nuclear abnormalities (hyperchromasia, large irregular nuclei, prominent nucleoids, high nuclear-to-cytoplasmic ratio), increased mitotic figures (including atypical mitoses), loss of normal tissue architecture/polarity, and tumor giant cells. It represents the extreme end of dedifferentiation, distinguishing malignant tumors from benign ones which typically retain differentiation. Anaplasia is used clinically as a grading criterion (poorly differentiated/high-grade tumors) and correlates with more aggressive clinical behavior, higher metastatic potential, and worse prognosis compared to well-differentiated tumors. It is distinct from dysplasia, which is a reversible, pre-neoplastic change with some preserved differentiation. Molecularly, anaplastic transformation often involves loss of tumor suppressor gene function (e.g., TP53, RB1) and genomic instability, leading to loss of normal growth regulation and cellular identity. Examples of highly anaplastic tumors include anaplastic thyroid carcinoma, glioblastoma multiforme, and small cell lung carcinoma. On Step 1/2, anaplasia is tested as part of tumor grading (grade reflects differentiation, stage reflects spread) and as a marker of malignancy along with invasion and metastasis.
Sources
- Robbins Basic Pathology
- Robbins and Cotran Pathologic Basis of Disease
- First Aid for the USMLE Step 1
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