Fig. 4

Histology and immunohistochemistry of primary tumors (P) and corresponding xenografts (X). Morphology: Assessed on HE sections, MO-4 and MO-25 primary tumors were classified as transitional due to the presence of meningothelial (lobulated architecture, clusters of syncytial cells, and meningothelial whorls) and fibroblastic features with collagen. MO-4 xenografts retained transitional features in all samples, and MO-25 retained traits in 60%. The transitional subtype can also contain psammoma bodies as seen in MO-25, which translated to the xenografts albeit in a lesser degree in comparison to the primary tumor. MO-27 primary tumor was classified as fibrous as it displayed bundles of collagen and maintained spindle cell morphology with few to no meningothelial nests or whorls. The xenografts had clear fibrous morphological traits in 4/14 cases but were dominated by the meningothelial subset, similarly to the transitional tumors. The MO-12 primary tumor was classified as microcystic because cells had elongated processes and vacuolated cytoplasm that resembles microcysts, which was also found especially in the largest (3/5) of the xenografts. Immunohistochemistry: All but one xenografted tumor showed consistent EMA staining. PR expression in xenografts was very heterogeneous within the primary tumors and between xenografts. Xenografted MO-4, MO-12, MO-25, and MO-27 regained PR in 89%, 40%, 20%, and 50% of animals, respectively, with a lower staining intensity in general. KI67 ranges (1–10%) were generally comparable between primary tumors and xenografts. SSTR2 displayed similar consistent staining scoring for MO-4. MO-12 and MO-25 showed a lower degree of staining intensity and also negative xenografts (Table 3). MO-27 showed well-matched high grade + 3 SSTR2 staining for the majority of xenografts. All xenografts showed similar negative (varying degree of unspecific) GFAP staining. OV: Overview, HE: Hematoxylin and Eosin, EMA: Epithelial membrane antigen, PR: Progesterone receptor, SSTR2: Somatostatin receptor 2, GFAP: Glial fibrillary acidic protein. Black bars: OV-X: 2,5 mm. Remaining slides: 100 \(\:{\upmu\:}\)m. Magnetic resonance images are T1-weighted with contrast.