A Study of Vestibular Schwannomas Using Positron Emission Tomography and Monoclonal Antibody Ki-67

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Objective: This study aimed to evaluate the role of positron emission tomography (PET) as an in vivo determinant of tumor aggressiveness and growth.

Study Design: The study design was a prospective pilot study.

Setting: Positron emission tomography was performed at the Clarke Institute of Psychiatry. All patients were treated at the Sunnybrook Health Science Centre. Both institutions are affiliated with the University of Toronto, Toronto, Canada.

Patients: The study consisted of five consecutive patients with vestibular schwannomas with tumor size of 1 cm or larger within the cerebellopontine angle. One was a recurrent tumor and four were primary tumors.

Interventions: Preoperative PET studies were conducted using 18-fluorodeoxyglucose (FDG) as a radionuclide tracer to measure glucose metabolism within tumors. Tumors were processed and immunostained against Ki-67 nuclear antigen: their proliferative potentials were quantified based on immunoreactivity of tumor cells.

Main Outcome Measures: Tumor metabolic activity on PET was compared with that of contralateral cerebellum to arrive at an FDG index. This number was compared with clinical parameters and Ki-67 reactivity.

Results: On PET, all tumors showed less metabolic activity than the cerebellum. The FDG uptake varied greatly between tumors independent of clinical parameters. All the tumors had a low proliferative index (<5%) with immunohistochemistry; there were quite a bit of intralesional variations in proliferative activities.

Conclusion: Large tumor size and recurrent disease did not correlate well with increased FDG uptake on PET. Similarly, they did not show increased cellular activities as expressed by Ki-67 immunostaining.

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