Fig. 2

Histopathological and molecular analyses of two patients in the regional cohort. a Four-year-old child (BPC A7) diagnosed with a PNET in the right hemisphere. MethPed classification (upper panel). H&E shows polymorphic, anaplastic cells and regions with necrotic areas; synaptophysin shows clonal positivity; GFAP mostly negative areas but also individual tumor cells with very strong expression and Ki-67 variable positivity (middle section, original magnification of the objective in all cases ×40). Magnetic resonance imaging (MRI) shows the location of the tumor, and Sanger sequencing chromatogram shows a HIST1H3B Lys27Met mutation in the tumor. Red arrow indicates the site of the mutation (lower panel). b Twelve-year-old child (BPC B5) diagnosed with a PNET in the brain stem. MethPed classification (upper panel). H&E shows cells variable in morphology with areas of rosette formation similar to Homer-Wright type; synaptophysin areas with granular cytoplasmic pattern and other areas with diffuse positivity as well as negative cells; GFAP positivity in a high number of cells indicates an unusual high incidence of astrocytic differentiation and high positivity of Ki-67 (middle section, objective original magnification ×40). Magnetic resonance imaging (MRI) shows the location of the tumor, and Sanger sequencing chromatogram shows a H3F3A Lys27Met mutation in the tumor. red Arrow indicates the site of the mutation (lower panel)