Clonal cytogenetic abnormalities in the plasma cell variant of Castleman disease

Castleman disease (CD) is widely regarded as a non-neoplastic process, yet clonal cytogenetic abnormalities have been rarely reported and are restricted to the hyaline-vascular variant. It remains unclear whether this reflects true rarity in such tumors - the fact that such cases are not routinely submitted for cytogenetic studies, or that suspension culture techniques are erroneously used rather than in situ cultures. We report a localized plasma cell variant of CD (PC-CD) with clonal abnormalities. A human immunodeficiency virus-negative 35-year-old man sought care for vague abdominal pain and was found to have an isolated 6-cm mesenteric mass. PC-CD was diagnosed by integrating clinical, laboratory, morphologic, and immunophenotypic studies. Flow cytometric, immunohistochemical, and molecular IGH@ gene rearrangement studies were all negative for a clonal B or plasma cell population. A cytogenetic in situ culture analysis revealed an abnormal karyotype: 46,XY,add(6)(p23),add(7)(p15),del(7)(p15),add(9)(q22)[4]/46,XY,inv(9)(p13q22)[2]/46,XY,-3,+r[2]/46,XY[3]. A cytogenetic suspension culture showed a normal karyotype. On the basis of the morphologic and immunophenotypic features, these genetic changes are attributed to the non-lymphoid cells, most probably of stromal, dendritic, or endothelial origin. Because the pathogenesis of PC-CD is not thought to typically involve the proliferation of these cell types, this is a new and unexpected finding and may provide pathogenetic insight.