The analysis of the distribution of patients with various MS phenotypes and of control subjects, according to CSF IL-6 detectability, demonstrated that IL-6 was more frequently present in CIS patients in comparison to controls [90/98 (91.8%) vs. 71/103 (68.9%), p = 0.001], RR-MS patients vs. controls [281/329 (85.4%) vs. 71/103 (68.9%), p = 0.001], SP-MS patients vs. controls [20/21 (95.2%) vs. 71/103 (69.7%), p = 0.013], and PP-MS [34/39 (87.2%) vs. 71/103 (68.9%), p = 0.027], respectively. Here, IL6 is linked to in situ carcinoma.