CXCR4 and neoplasm: In addition, circadian variations of stromal cell derived factor 1 (SDF1) and chemokine receptor 4 (CXCR4) plasma levels [144], together with downregulation of PC-associated expression of integrins like CD11a, CD11c, CD29, CD49d and CD49e [144], and activation antigens (such as CD38 and CD27) [21,144] on CTPC vs. BM tumor PC, might also favor the release of tumor PC into the circulation.