Progressive transformation of the germinal center of extranodal organs: a clinicopathological, immunohistochemical, and genotypic study of 14 cases.

Progressive transformation of germinal center (PTGC) usually affects the peripheral lymph nodes. Little is known about the extranodal PTGC. To clarify the clinicopathological and molecular findings of extranodal PTGC, we studied 14 such cases. Using formalin-fixed, paraffin-embedded sections, we carried out histological and immunohistochemical examinations, as well as in situ hybridization (ISH) and polymerase chain reaction (PCR). Eleven patients were female, and three were male. They were between 44 and 77 years old, with a mean age of 62 years. The large intestine (n=7) was the most frequently involved tissue, followed by skin (n=2) and subcutaneous soft tissue (n=2). Oral cavity, Waldeyer ring, and orbit were affected in one case each. Histologically, 13 cases contained both early stage PTGC and late stage PTGC. The remaining 14th case contained only late stage PTGC. Expansion of the marginal zone was identified in three cases. Immunohistochemical study demonstrated the reactive nature of the B-cells in all 14 lesions. However, PCR study revealed immunoglobulin heavy chain (IgH) gene rearrangement in one of our 14 cases. There was no development of B-cell lymphoma in one lesion with IgH rearrangement. ISH study demonstrated Epstein-Barr virus-encoded small RNA+ cells in three lesions. Compared with PTGC of the peripheral lymph node, PTGC of extranodal sites was characterized by a female predominance, an older age group, and the presence of numerous PTGC at the affected sites. However, the histological findings of extranodal PTG were similar to those of lymph node PTGC. The clinicopathological findings of the extranodal PTGCs appeared to be different from those of lymph node PTGC.