Plasmacytoid dendritic cells (PDCs) have perplexed pathologists for decades, undergoing multiple adjustments in nomenclature as their lineage and functions have been characterized. Although PDCs account for less than 0.1% of peripheral blood mononuclear cells, they serve as a principal source of
interferon-alpha and are also known as
interferon-I producing cells (IPCs). Upon activation in vitro, they can differentiate into dendritic cells, and recent studies have substantiated a potential role in antigen presentation. Thus, PDCs may act as a link between innate and adaptive immunity. Normally found in small quantities in primary and secondary lymphoid organs, PDCs accumulate in a variety of inflammatory conditions, including Kikuchi-Fujimoto
lymphadenopathy, hyaline-vascular
Castleman disease, and
autoimmune diseases, and in certain
malignancies such as classical
Hodgkin lymphoma and
carcinomas. Demonstrating potential for neoplastic transformation reflective of varying stages of maturation, clonal proliferations range from PDC nodules most commonly associated with
chronic myelomonocytic leukemia to the rare but highly aggressive
malignancy now known as blastic plasmacytoid dendritic cell
neoplasm (BPDCN). Formerly called blastic natural killer cell
lymphoma or CD4/CD56 hematodermic
neoplasm, BPDCN, unlike natural killer cell
lymphomas, is not associated with
Epstein-Barr virus infection and is generally not curable with treatment regimens for non-Hodgkin
lymphomas. In fact, this entity is no longer considered to be a
lymphoma and instead represents a unique precursor
hematopoietic neoplasm. Acute
leukemia therapy regimens may lead to sustained clinical remission of BPDCN, with
bone marrow transplantation in first complete remission potentially curative in adult patients.