From the archives of MD Anderson Cancer Center: Stroma-rich hyaline vascular Castleman disease followed by indolent T-lymphoblastic proliferation and detection of PDGFRB mutation.

Castleman disease (CD) is a complex group of at least four lymphoproliferative diseases of which unicentric CD is most common. Morphologically, unicentric CD can be subdivided into hyaline-vascular and mixed/plasmacytic variants. Indolent T-lymphoblastic proliferation (iT-LBP) is a benign, extrathymic expansion of T-lymphoblasts that sometimes can be associated with CD. Cases of iT-LBP do not exhibit morphologic atypia or a destructive growth pattern, lack evidence of monoclonality or recurrent genetic abnormalities and are regarded as reactive processes. We describe a 49-year-old woman who developed a pelvic mass. Needle biopsy showed stroma-rich hyaline-vascular unicentric CD. Two years later, the mass enlarged, and an incisional biopsy revealed a diffuse proliferation of immature lymphoblasts positive for TdT, CD4 and CD8 without immunophenotypic evidence an aberrant T-cell or B-cell population. There was no morphologic evidence of CD, however, a spindle cell proliferation was present in the background. Next generation sequencing showed a PDGFRB N666S mutation suggesting the presence of residual CD. We present this case because it highlights the known association between CD and iT-LBP and the detection of PDGFRB mutation supports the interpretation that the iT-LBP likely arose from hyaline-vascular CD.