Measures
The independent variables measured were age at the time of diagnosis, race, gender, Yost quintile, stage of cancer at diagnosis, histological type of tumor, tumor grade, and treatment received: radiotherapy, chemotherapy, and surgery. Study subjects were categorized into four age groups: 01-04 years, 05-09 years, 10-14 years, and 15-19 years. Race/ethnicity was categorized as non-Hispanic white, Hispanic, African American, with Asian or Pacific Islander/ American Indian/Unknown race all grouped together as “Other” due to the small numbers in these groups. Yost quintile is categorized into five groups with Group 1 having the lowest SES (<20th percentile) and Group 5 having the highest SES (>80th percentile).25
Tumor grade was reclassified as low grade (Well differentiated: Grade I and Moderately differentiated: Grade II) and high grade (Poorly differentiated: Grade III and Undifferentiated anaplastic Grade IV) tumor. Based on the treatment received, chemotherapy and radiotherapy were simply grouped as “yes” and “no”. Patients were classified as yes if they received the various types of radiotherapy: beam radiation, radioactive implants, radioisotopes, combination of beam with implants or isotopes, or radiation not otherwise specified (NOS). Surgery status was classified as local excision/excisional biopsy, subtotal tumor resection, gross total tumor resection, partial lobectomy, total lobectomy (includes 86 cases who had unspecified surgery), or surgery not done/unknown.
Due to small sample sizes, histological tumor types were grouped as diffuse astrocytoma (protoplasma, fibrillary) and mixed glioma, anaplastic astrocytoma and glioblastoma, pilocytic astrocytoma, astrocytoma NOS and unique variants, ependymoma/anaplastic ependymoma/ependymoma variants, embryonal/primitive/medulloblastoma, glioma NOS.
Our dependent variable was overall survival. Survival was defined as the time from diagnosis until death of a study subject or the end of the follow-up period (November 2018).