mTOR activation is increased in pilocytic astrocytomas from older adults compared with children.

BACKGROUND

Recent studies suggest that the behavior and biology of WHO grade I pilocytic astrocytomas (PAs) in adults is different than that associated with grade I PAs in children.

METHODS

We evaluated Ki-67 labeling, BRAF abnormalities, isocitrate dehydrogenase R132 immunoreactivity phosphorylation (activation) of p44/42 mitogen activated protein kinase (MAPK), and mammalian target of rapamycin (mTOR) in formalin-fixed tissue from 21 adult (18 years or older, mean age 37 years) and 10 children (mean age 9.4 years) WHO grade I PAs.

RESULTS

The mean Ki-67 labeling was 4.8% in adults and 3.8% in children. There was no significant difference between Ki-67 labeling in children and adults or either subgroups of adults. No differences were found in phospho p44/42MAPK in adult subgroups (18-33 years and 34 and older) compared to children. Activation/phosphorylation of mTOR was biphasic in adults being significantly lower than children in young adults but significantly higher than children in older adults (age 34 and older).

CONCLUSIONS

Identifying mTOR phosphorylation/activation may represent a difference in biology and a new marker to guide chemotherapy with recently approved mTOR inhibitors.