Follicular dendritic cell sarcoma and its response to immune checkpoint inhibitors nivolumab and ipilimumab.

Follicular dendritic cell sarcoma (FDCS) is a rare and unusual cancer that arises from sustentacular cells of the lymph node that present antigen to B cells, rather than lymphocytes themselves. While surgery for primary disease is still paramount in primary management, for unresectable, recurrent and metastatic tumours, FDCS is frequently treated with anthracycline-based lymphoma chemotherapy regimens. In recent years, it is clear that Programmed Cell Death 1 (PD1)-directed immune checkpoint inhibitors (ICIs) are active in Hodgkin lymphoma, but significantly less active in non-Hodgkin's lymphoma. These data raised the question of whether FDCS respond to ICI therapy. We present two patients with FDCS who were treated with nivolumab and ipilimumab with evidence of tumour response. These cases also highlight the difficulty in arriving at a proper diagnosis, emphasising the need for expert review of pathology to optimise treatment for these and other patients with sarcoma.