MIB1 and p53 immunoreactivity in protoplasmic astrocytomas

Pure protoplasmic astmqtomas am a group of rarely encountered low grade astfocytic neoplasms. Relatively few studies have speclfically examined this subset of tumors. A series of 18 protoplasmic astrocytomas in 14 males and four females (age range 2.5–52, mean 22 years) were studied in order to examine MlB1 (a marker of cell proliferation) and p53 (a tumor suppressor gene) immunoreactivity. All patients presented with seizures (mean duration 94 months) and three with headaches also. Elght tumors were located in the temporal lobe and six in the frontal lobe. All tumors were characterized by a proliferation of astrocytes with round nuclear contours arranged against a microcystic background. Only rare focl of mild vascular proliferation (3 tumors), rare mitotic figures (1 tumor), and mild nuclear atypia (3 tumors) were observed. Most tumors were primarily cortical in location. Necrosls was not seen in any of the tumors. MiB1 indices (number of MiB1 positive tumor cells/1000 tumor cells evaluated x100) ranged from 0 to 4.3 (mean 0.7); in five tumors, no MiB1 staining was observed. p53 immunoreactivity was noted in 5 of 18 tumors (28%). Five patients received adjuvant radiation therapy and one adjuvant chemotherapy. At last known follow-up, 11 patients are alive with no evidence of residual tumor (mean 70 months), six patients are alive with evidence of residual tumor (mean 58 months), and one patlent died of complications unrelated to the tumor (36 months) postoperatively. Based on these findings, the conclusions presented are as follows: (i) MlBl indices are generally low in these tumors, corroboratlng the clinical impredon of a slow growing neoplasm; and (ii) p53 immunoreactivity is obsewed in a minority of protoplasmic astrocytomas.