Phenotype and immunophenotype of the most common pediatric tumors.

Pediatric tumors are heterogenous and can be quite varied in appearance. However, those in the infamous "small round blue-cell tumor" group, with their hyperchromatic nuclei and small amount of cytoplasm can be challenging, and their diagnosis and prognostication require cost-efficient and focused immunohistochemistry and ancillary testing. Ideally, ample material should be obtained for routine histology and ancillary testing, including immunohistochemistry, fluorescent in situ hybridization, fresh tissue for cytogenetic studies, and snap-frozen tumor for DNA/RNA extraction both for routine molecular testing (ie, reverse-transcription PCR studies), as well as future research study protocols (genome wide studies, targeted gene sequencing). This review focuses on the main pediatric tumors with emphasis on immunophenotype, keeping in mind that a directed panel approach yields the highest yield with combination of clinical history, histologic features, and ancillary molecular testing.