B2M and Familial prostate cancer: Major histocompatibility complex class I (MHC-I) molecules play a pivotal role in presenting tumor neoantigens to immune cells, and B2M is essential for the proper assembly and presentation of MHC-I molecules on the cell surfaces.22 Its absence hinders CD8+ T-cell recognition, impairing a key pathway of immune surveillance.23 While B2M loss is somewhat less common in renal cancers compared to bladder and prostate cancers, renal cell carcinomas may exhibit other alterations that affect MHC- I presentation.