Pineal parenchymal tumor of intermediate differentiation showing malignant progression at relapse.

Pineal parenchymal tumors of intermediate differentiation (PPTID) are extremely rare tumor entities and only limited data are available regarding their pathologic features and biologic behavior. In this report, we describe a case of PPTID transformed into pineoblastoma at relapse in a 47-year-old woman, focusing on the comparison of histologic and immunohistochemical features between the first and recurred tumors. The first tumor in February 2004 exhibited diffuse sheets of relatively uniform, small cells with moderately high cellularity and mild nuclear atypia, and no mitoses or necrosis. Immunohistochemically, the tumor cells showed diffuse staining for neuron-specific enolase (NSE), synaptophysin and chromogranin, and the MIB-1 labeling index was 3%. The diagnosis was PPTID. On the other hand, 4 years later, the recurred tumor had morphologic features of undifferentiated small cell histology with high mitotic activity and prominent necrosis. Immunohistochemically, the tumor cells showed only focal, weak staining for NSE, synaptophysin and chromogranin, and the MIB-1 labeling index was 19%, all of which were the features of pineoblastoma. This case clearly indicates that PPTID can be transformed without limit into pineoblastoma at relapse in a clinical aspect, and PPTID is closely related to pineoblastoma on a continuous spectrum in a histogenetic aspect.