PROX1 and myeloid sarcoma: The availability and validation of novel lymphatic marker proteins (podoplanin/D2-40, LYVE-1, VEGFR-3, VEGF-D, Ang-2) and transcription factors (Fox-C2, Prox-1) [33-36] have rapidly expanded our understanding of lymphatics and allow investigation of their roles in MS pathophysiology.