Molecular Diagnostics in Pediatric Cytopathology
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Given that pediatric malignancy is rare, most pediatric fine-needle aspiration (FNA) biopsies will be benign. Of pediatric malignancies, the most common are hematolymphoid malignancies, central nervous system (CNS) tumors, neuroblastoma, and Wilms’ tumor. Leukemias and CNS tumors are unlikely to be encountered by the cytopathologist, so this chapter will focus on pediatric lymphomas and solid organ malignancies, particularly those in which molecular studies play an important role. When evaluating a pediatric FNA, it is important to consider collecting material for ancillary studies including cell block, flow cytometry, cytogenetics, fluorescence in situ hybridization (FISH), molecular testing, as well as fresh frozen tissue, especially in the setting of a potentially neoplastic process. There are three main cytomorphologic patterns that will help guide your workup and differential diagnosis, including small round blue cell morphology (both lymphoid and nonlymphoid), large epithelioid morphology, and spindle cell morphology. Although many diagnoses can be made using a combination of cytomorphology and immunohistochemical stains, there are several pediatric malignancies that require molecular studies for prognosis, therapeutic decisions, and/or definitive diagnosis or subtyping.
KeywordsBiopsy Children Core-needle biopsy Cytology Cytopathology Fine-needle aspiration FISH Fluorescence in situ hybridization FNA In situ hybridization Molecular Pathology Pediatric Rapid on-site evaluation ROSE Small biopsy
v-Raf murine sarcoma viral oncogene homolog B
Central nervous system
Fluorescence in situ hybridization
Immunoglobulin heavy chain
Langerhans cell histiocytosis
Polymerase chain reaction
Papillary thyroid carcinoma
Roswell Park Memorial Institute
Special thanks to all of the staff in the UPMC molecular pathology and ISH/FISH laboratories for their assistance with the preparation of the images in this chapter.
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