Similar to RRMS, B cells from CIS patients with a very rapid onset of clinically definite MS (CDMS) (“high‐risk CIS,” n = 16) showed 1.5‐fold increased CXCR4 (p = 0.014, Fig. 2A) and 1.3‐fold reduced CD74 surface levels (p = 0.004, Fig. 2B) compared to CIS patients with slow or no onset of CDMS (“low‐risk CIS,” n = 17). Here, CD74 is linked to in situ carcinoma.