Unusual extramedullary hematopoietic neoplasms in lymph nodes

Myeloid, plasma cell, and lymphoblastic neoplasms are expected findings in bone marrow but are much less commonly diagnosed as primary processes in lymph nodes. The objective of this review is to aid pathologists in recognizing common hematopoietic neoplasms in the unusual setting of initial presentation in lymph nodes. Review of historical background and evolution of testing strategies is presented to improve understanding of the need for accurate diagnosis and classification using current nomenclature. The review is based on peer-reviewed literature and the personal experience of the authors. The University of Minnesota Medical Center, Fairview provides lymph node diagnostic consultation services for its busy oncology and therapeutic hematopoietic cell transplant divisions serving patients from around the globe. Although readily recognizable when they present in bone marrow, myeloid leukemia in the form of myeloid sarcoma, plasmacytoma, and lymphoblastic lymphoma can create diagnostic and classification challenges when they present as primary lymph node pathologies. Use of all diagnostic tools may be necessary to ensure accurate and reproducible diagnoses.