Abstract
With an annual cumulative occurrence of approximately 15,000 in North
America, all childhood cancers are rare. Very rare cancers as defined by
both the European Cooperative Study Group for Rare Pediatric Cancers
(EXPeRT) and the Children’s Oncology Group (COG) fall into two principal
categories: those so uncommon (fewer than 2 cases/million) that their
study is challenging even through cooperative group efforts (e.g.
pleuropulmonary blastoma, desmoplastic small round cell tumor) and those
that are far more common in adults and therefore rarely studied in
children (e.g. thyroid, melanoma, gastrointestinal stromal tumor).
[1](#ref-0001) Treatment strategies for these latter tumors are
typically based on adult guidelines, although the pediatric variants of
these tumors may harbor different genetic signatures and demonstrate
different behavior. If melanoma and differentiated thyroid cancer are
excluded, other rare cancer types account for only 2% of the cancers in
children aged 0 to 14.[1](#ref-0001) This article highlights
several of the most common rare tumor types.