Abstract: Provided are methods for assigning a subject having idiopathic multicentric Castleman disease (iMCD) to a group having a higher or lower probability of responding to treatment for iMCD using measured quantities of CXCL13. Also disclosed are methods of treating idiopathic multicentric Castleman disease (iMCD) in a subject in need thereof comprising administering to the subject an inhibitor of CXCL13 or of CXCR5. Also provided herein are methods for assigning a subject having idiopathic multicentric Castleman disease (iMCD) to a group having a higher or lower probability of responding to treatment for iMCD using measured quantities of specified biomarkers. The present disclosure also provides methods of treating idiopathic multicentric Castleman disease (iMCD) in a subject in need thereof comprising administering to the subject an inhibitor of the JAK-STAT3 pathway. Also disclosed are methods for assessing the absence or presence of iMCD in a subject.