Expression of Ki-67 antigen and vascular endothelial growth factor in sporadic and neurofibromatosis type 2-associated schwannomas
Neurofibromatosis type 2 (NF2) is a formidable disease with considerable morbidity. Among tumors associated with NF2, schwannomas are the most difficult to treat because they are multiple and tend to recur. Vascular endothelial growth factor (VEGF) has been reported to act as a survival factor for Schwann cells. We, therefore, investigated VEGF expression in NF2-associated and sporadic schwannomas. We also evaluated the proliferative potential of these tumors by Ki-67 staining (MIB-1 labeling index) and microvascular density by CD34 staining. Immunohistochemistry was performed in 8 schwannomas from 6 NF2 patients, 2 schwannomas from 2 probable NF2 patients and 10 sporadic schwannomas. VEGF immunostaining was present in most schwannomas: all sporadic schwannomas and 8 of 10 schwannomas from NF2 or probable NF2 patients (NF2 group). No difference was evident in VEGF staining between the 2 groups. MIB-1 labeling index was significantly higher in the NF2 group (3.8 +/- 1.7) than the sporadic group (2.0 +/- 1.0, p < 0.01). Microvascular density was higher in the NF2 group (12.9 +/- 6.0) than the sporadic group (9.4 +/- 3.5), but not significantly (p = 0.06). Although VEGF alone cannot explain the higher proliferative potential in NF2-associated schwannomas, VEGF could be a factor influencing the proliferative potential of schwannomas.