B2M and cancer: Moreover, oncogenic exosomes contain factors known to regulate the pre-metastatic niche (S100A4, F3, ITGβ5, and ANXA1), clinically-relevant proteins which correlate with poor prognosis (CLDN1, MUC1) as well as protein networks involved in various cancer hallmarks including proliferation (CLU, CAV1), invasion (PODXL, ITGA3), metastasis (LAMP1, ST14) and immune surveillance escape (B2M).