Study	Tests included	Tumour type	Tumour grade	++++	+++‐	++‐+	+‐++	‐+++	++‐‐	+‐‐+	‐‐++	‐++‐	‐+‐+	+‐+‐	+‐‐‐	‐+‐‐	‐‐+‐	‐‐‐+	‐‐‐‐	Total with test results	Notes
Blesa 2009	A: aCGH B: FISH C: MLPA D: PCR	Anaplastic oligodendroglioma	III	0	0	0	1	0	0	0	0	0	0	0	0	0	0	0	1	2	Some differences between Table 2 in text and the Supplementary Table. Since the Supplementary Table had more information, we extracted from this. Relative deletions on FISH were classified as a negative result as they were not absolute deletions.
		Oligodendroglioma	II	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	1
		Anaplastic oligoastrocytoma	III	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	2	2
Duval 2014	A: FISH (combination cut‐off based on number of cells showing a deletion) B: FISH (ratio cut‐off based on the ratio of signals for 1p to 1q and 19q and 19p) C: FISH (immunoFISH with combination cut‐off) D: FISH (immunoFISH with ratio cut‐off)	Oligodendroglioma	II	6	0	1	0	0	0	0	0	0	0	0	0	0	0	0	4	11	FISH assessments were made independently by 2 observers. In 1 case, a participant was classified as having the codeletion by 1 observer but not the other when using the ratio method to interpret the results of ImmunoFISH. Raw data were available from the 2 observers, and we averaged the raw data and applied the reported cut‐off to come to a consensus classification.
		Anaplastic oligodendroglioma	III	13	0	0	0	0	1	0	0	0	0	0	0	0	0	0	8	22
		Glioblastoma with oligodendroglioma component	IV	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	2	3
Hatanpaa 2003a (assay development and non‐blinded validation cohort)	A: CGH B: FISH C: PCR (comparison to normal DNA) D: PCR (microsatellite)	Astrocytoma	II	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	2	2	Participants from Smith 1999. We removed D1S534 from the regions analysed by PCR with comparison to normal DNA as this was not used to assess 1p/19q status. We used the histological diagnosis from this paper (rather than from Smith 1999).
		Astrocytoma	III	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	1
		Oligodendroglioma	II	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	2
Hatanpaa 2003b (blinded validation cohort)	A: CGH B: FISH C: PCR (comparison to normal DNA) D: PCR (microsatellite)	Astrocytoma	II	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	1	Participants from Smith 1999. We removed D1S534 from the regions analysed by PCR with comparison to normal DNA as this was not used to assess 1p/19q status. We used the histological diagnosis from this paper (rather than from Smith 1999). Note: 1 of the ++++ tumours (T246, oligodendroglioma) (quote) "was found to have partial LOH on 1p, a finding confirmed by comparison with the allelic pattern derived from normal tissue dissected from this case (Table 2). In this tumor, heterozygosity was only preserved at one locus of eight assessed on 1p and 19q. In light of previous studies (Bello et al, 2000; Bigner et al, 1999; Smith et al, 1999), this tumor may represent a rare aberration from the usual extent of LOH on 1p in oligodendrogliomas. Although the clinical significance of this finding of partial LOH is not known, the tumor is probably best classified as having a high likelihood of clinically relevant LOH on 1p, considering that heterozygosity was preserved at only one locus and that the tumor was histologically an oligodendroglioma".
		Mixed	II	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	2	2
		Oligodendroglioma	II	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	3
Hatanpaa 2003b (blinded validation cohort)	A: CGH B: FISH C: PCR (comparison to normal DNA) D: PCR (microsatellite)	Mixed	III	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	1	Participant from Burger 2001. We have used the histological diagnosis from this paper (rather than from Burger 2001).