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).