Circadian rythms in myeloma. Circadian distribution of CTCs (A), CD34⁺ HSCs and progenitor cells (B), SDF1α plasma levels (C), and the levels of CXCR4 surface expression per CTCs (D) in MM patients (N = 6). All measurements started at 4:00 pm and they were repeated every 4 hours up to 12:00 pm, the next day (when the patients initiated antimyeloma therapy). The 4:00 pm and 8:00 pm time points are repeated at both sides of all 4 graphics to facilitate viewing of the circadian variations.