CXCR4 and Waldenstrom macroglobulinemia: The non-canonical signaling of truncated GOF CXCR4 variants is well-characterized within the context of WHIM syndrome and Waldenström's macroglobulinemia, where the hyperfunctional phenotype of truncated CXCR4 results in sequestration of cells in BM niches (12, 33, 39, 41–44).