Table 1. Overview of Samples Included in Pool Formation.

	acute lymphoblastic leukemia	primary brain tumor	nontumor control
subgroup	30 unique patients	18 unique patients	30 unique individuals
age	median: 5.3 years	median: 8.5 years	median: 15.3 years
	interquartile: 3.4–8.2 years	interquartile: 4.6–15.4 years	interquartile: 3.0–26.0 years
	range: 0.1–17.1 years	range: 0.4–17.7 years	range: 0.0–35.2 years
sampling method	30 lumbar puncture	8 extraventricular drainage	30 lumbar puncture
		10 perioperatively
pathology	day 0	anaplastic ependymoma	sterile CSF
	• FCM-positive: n = 11	• n = 4	• erythrocyte count <300 × 106/L
	• FCM-negative: n = 11	atypical teratoid rhabdoid tumor	• nucleated cells <4 × 106/L
		• n = 1
		craniopharyngioma
		• n = 2
	day 15 (induction therapy)	diffuse intrinsic pontine glioma
	• FCM-positive n = 4	• n = 2
		gliomas
	• FCM-negative: n = 4	• n = 2
		medulloblastoma
		• group 3, n = 1
		• not WNT/not SHH
		n = 2
		pilocytic astrocytoma
		n = 4
total volume	total 15 mL:	total 15 mL:	total 15 mL:
	day 0	anaplastic ependymoma
	• FCM-positive: 5.5 mL	• 3.5 mL
	• FCM-negative: 5.5 mL	atypical teratoid rhabdoid tumor
		• 0.5 mL
		craniopharyngioma
		• 1.5 mL
	day 15 (induction therapy)	diffuse intrinsic pontine glioma
	• FCM-positive: 2 mL	• 2 mL
	• FCM-negative: 2 mL	gliomas
		• 2 mL
		medulloblastoma
		• group 3, 1 mL
		• not WNT/not SHH 1.5 mL
		pilocytic astrocytoma
		• 3.0 mL