Cyclin D1 and MIB-1 immunohistochemistry in pilocytic astrocytomas: a study of 48 cases

Pilocytic astrocytoma is an infrequently encountered, generally low-grade neoplasm. No study has extensively looked at both cyclin D1 and MIB-1 labeling indices in pilocytic astrocytoma and their relation to clinical outcome. This study retrospectively examines the clinicopathologic features of 48 patients with pilocytic astrocytoma including MIB-1 (cell proliferation marker) and cyclin D1 (protein that regulates progression from G1 to S phase of the cell cycle) immunohistochemistry. Of 48 patients (27 females and 21 males; mean age, 12.7 years; age range, 2 to 57 years), 26 initially underwent gross total resection; 17, subtotal resection; four, biopsy alone; in one patient, the extent of tumor resection was unknown. Histological features observed included Rosenthal fibers (83.3%), granular bodies (75%), vascular sclerosis (56.2%), vascular proliferation (56.2%), prominent nuclear pleomorphism (14.6%), necrosis (10.4%), and identifiable mitotic figures (2.1%). MIB-1 labeling indices (n=45) (positive staining tumor nuclei per 1,000 nuclei evaluated) ranged from 0 to 3.5% (mean, 0.6%); seven tumors had a labeling index greater than 1.0%. Cyclin D1 labeling indices (n=45) ranged from 0 to 0.8% (mean, 0.1%). Most tumors (N=29, 66.7%) had no immunostaining. At last known follow-up, 27 patients were alive with no evidence of disease (mean, 49.2 months), 17 patients were alive with evidence of disease (mean, 36.8 months), three died with tumor at 2, 22, and 156 months, and one patient was lost to follow-up. Eight patients had at least one tumor recurrence requiring additional surgery; seven of these patients had an initial subtotal resection. In summary, MIB-1 labeling indices were generally low (mean, 0.6%) and are reflective of the slow growth of the tumors. Cyclin D1 immunostaining does not appear to be significantly increased in pilocytic astrocytoma. Adverse outcome in patients with pilocytic astrocytoma may be related to extent of surgical resection and does not seem to correlate with histology, MIB-1 labeling indices, or cyclin D1 immunoreactivity.