Monarch Disease Ontology id MONDO_0006247 (histiocytic and dendritic cell neoplasm) is rare tumors that affect the hematopoietic and lymphoid tissues. The cells of origin are the histiocytes and accessory cells. They can occur at any age and show no significant variations in geographical distribution. This category includes the histiocytic sarcoma, Langerhans cell histiocytosis, Langerhans cell sarcoma, interdigitading dendritic cell sarcoma/tumor, follicular dendritic cell sarcoma/tumor, and dendritic cell sarcoma, not otherwise specified. (WHO, 2001). Also known as: histiocytic and Dendritic cell neoplasms, histiocytic and Dendritic cell tumors, histiocytic and Dendritic cell tumours.