34 How does the 2007 WHO classification differ from earlier versions? • Includes CNS primary tumors only; peripheral neuroblastic tumors are not included • Includes new entities and variants • Differentiates entity, variant, and pattern of differentiation What is an “entity?” Not only a distinct histopathological pattern but also a distinct morphology based on age, location, and clinical signs (e.g., extraventricular neurocytoma) What is a “variant?” Part of a defined entity that presents with distinct morphology and some significant clinical difference (e.g., anaplastic medulloblastoma) What is a “pattern of differentiation?” A distinct histopathological pattern without clinical significance, such as a genetic or prognostic difference (e.g., small cell glioblastoma) What are some of the new entities? • Angiocentric glioma • Papillary glioneuronal tumor • Rosette-forming glioneuronal tumor of the fourth ventricle • Papillary tumor of the pineal region • Pituicytoma • Spindle cell oncocytoma of the adenohypophysis (See Chapter 35) What are some of the new variants? • Pilomyxoid astrocytoma • Anaplastic medulloblastoma • Medulloblastoma with extensive nodularity (See Chapter 35) What syndrome was added to the familial tumor syndromes typically involving the nervous system? Rhabdoid tumor predisposition syndrome Who contributed to the classification? An international working group of 25 pathologists and geneticists together with more than 70 experts worldwide Despite an increased emphasis on genetics, what remains the gold standard of WHO tumor grading? Morphology What is the purpose of histological grading? To facilitate the prediction of behavior of the neoplasm and thus optimal selection of therapies1 What other criteria may be useful to predict prognosis? • Patient’s age • Radiological features (e.g., contrast enhancement) • Extent of surgical resection • Genetic alterations • Proliferation indices • Performance status and tumor location What are some of the atypical cell findings that may be helpful in establishing histological grade? • Increased cellularity
Basic Concepts
34.1 WHO Classification
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