Germ Cell Tumors in Adolescents and Young Adults.

Germ cell tumors (GCTs) represent a group of biologically complex malignancies that affect patients at different sites within the body and at different ages. The varying nature of these tumors reflects their cell of origin which is the primordial germ cell, which normally gives rise to ovarian and testicular egg and sperm producing cells. These cells retain an ability to give rise to all types of human tissues, and this is illustrated by the different kinds of GCTs that occur. In adolescent and young adult (AYA) patients, GCTs predominantly present as testicular, ovarian or mediastinal primary GCTs, and represent some of the most complex therapeutic challenges within any AYA practice. The varying types of GCTs, defined by primary site and/or age at presentation, can look very similar microscopically. However, there is growing evidence that they may have different molecular characteristics, different biology and different requirements for curative treatments. Whilst in adult testicular GCTs there is evidence for an environmental cause during fetal development and a genetic component, these causative factors are much less well understood in other GCTs. GCTs are some of the most curable cancers in adults, but some patients exhibit resistance to standard treatments. Because of this, today's clinical research is directed at understanding how to best utilize toxic therapies and promote healthy survivorship. This chapter explores the biology, behavior and treatment of GCTs and discusses how the AYA group of GCTs may hold some of the keys to understanding fundamental unanswered questions of biological variance and curability in GCTs.