Process of criteria development. An international working group with 34 leading physicians, pathologists, and clinicians was created to develop the diagnostic criteria for iMCD. A modified Delphi Method & Nominal Group Technique was selected to guide the criteria development process. A total of 244 patients’ clinical data were gathered along with lymph node slides from 88 cases. Two working group meetings were held to establish an agreed-upon diagnostic criteria. Postmeeting analyses were performed to reapply the agreed-upon diagnostic criteria to 79 cases from NCT01024036 and to use the newly defined histopathologic spectrum to subtype cases. The consensus criteria and results from analyses were compiled into a manuscript that was reviewed by the full expert working group.