CD99 and primitive neuroectodermal tumor: Other less specific markers such as CD56, CD9, CD57, CD81, CD99 also contributed to some differential diagnoses, e.g. the distinction between neuroblastoma and RMS (CD56,CD57,CD81) and between PNET and both RMS (CD9) and neuroblastoma (CD99, CD56, CD81 and CD57) (Figure 1I–J; Figure 2).