Clinico-pathological feature of pilomyxoid astrocytomas: three case reports.

Pilomyxoid astrocytoma (PMA) is a newly identified variant of pilocytic astrocytoma (PA). We report three cases of PMA with comparison to seven cases of PA in terms of their clinicopathological features. The three cases occurred at the ages of 2, 36 and 6 years, and their tumors were located in the left basal ganglia, the pineal gland, and the cerebellum, respectively. They were diagnosed PMA by surgical specimens that showed a characteristic monomorphous architecture with an angiocentric growth pattern and myxoid background. One patient developed localized relapse at 6 months after the surgery, but the other patients remained alive without tumor progression more than 5 years after treatment. In analysis of the immunohistochemical association in PMA and PA, no specific staining was found to be useful for differential diagnosis of PMA from PA. The expression of biomarkers including O-6-methylguanine-DNA methyltransferase, p53, MIB-1, and EGF receptor neither distinguished PMA from PA nor correlated with outcome. But almost all PMA and PA that demonstrated prominent positivity for nestin showed a high MIB-1 labelling index (LI), and four of these five patients suffered a relapse in the early phase. These results suggest that immunohistochemical expression of nestin and MIB-1 LI may correlate with the aggressiveness of the tumor in PA and PMA.