Pseudoprogression of low-grade gliomas after radiotherapy

Increasing mass effect following radiation therapy (RT) in patients with low-grade gliomas (LGGs) can be mistaken for tumor progression and/or malignant degeneration. Distinguishing pseudoprogression (PP) from true progression is crucial, with vastly different treatment approaches and prognoses.

Patients treated with RT for LGGs through the Children's Hospital of Pittsburgh Neuro-Oncology Program are considered to have PP and managed conservatively if they develop increased mass effect within 3 years of RT. Pre-RT tumor area was compared to the maximum tumor size following RT and the size on the last follow-up scan by a central reviewer.

Twenty-four children, median age 13 years, received external beam RT for LGG between March 2000 and August 2011. Thirteen patients (54.2%) developed an increase in tumor size compared to baseline beginning at a median of 6 months after RT and lasting for a median of 2.1 years (range 6.5 months to 5.1 years). Maximum tumor enlargement occurred at a median of 8 months after RT, with a range (5 months to 4.2 years). In all 13 cases, the tumor eventually decreased in size without additional anti-tumor therapy. Two patients (8.3%) developed true tumor progression. With a median follow-up of 4.9 years (range 1.0-12.4 years), all patients are alive.

Pseudoprogression occurred in more than half of the children with LGG following RT, typically beginning within 8 months and often running a very protracted course. Late presentations can also occur.