Papillary meningioma in the dog: A benign histotype with aggressive behavior

Papillary meningioma (PM) is one of the most aggressive variants of meningioma in humans and classified as grade III (WHO) based on brain invasion, local recurrence and distant metastases. To date the biological behaviour of PM is still not clear in dogs. This study correlates the histomorphological findings and cell adhesion (E-cadherin, N-cadherin) and invasion molecule (Doublecortin) expression investigated by IHC with follow up data of 16 PMs of dogs obtained by surgical excision (8 cases) or necropsy (8 cases). FFPE 5 µm sections were stained with H&E. Additional 4 µm sections were used for IHC (ABC method, Dako, Milan, Italy). PMs accounted for 18% of our archived meningiomas. Based on histological criteria adopted by human WHO classification, 7 tumors (43,8%) and 9 tumors (56,2%) were morphologically classified as grade I and as grade II, respectively. In surgical cases recurrence was observed in 87.5% and the mean survival time (MST) was 10.8 months. Five recurrent surgical PMs showed necrosis up to 50% of the tumor. Non-surgical cases showed a MST of 24 days. An apparent negative correlation between E-cadherin and N-cadherin expression was found in tumors with low survival time. Despite benign histological findings, we observed an aggressive behavior of PM also in dogs, especially for animals that were not submitted to surgery. Therefore surgical resection is strongly recommended. As in humans, the biological malignancy of canine PM seems to be correlated to intratumoral necrosis. Finally, we might suppose a “cadherin-switch” involvement in the biological progression of canine PM.