So we finally managed to do genetic tests on grandpa's tumor cause one hospital decided to do it before they start him on chemo (his surgery was back in early April) and it turned out to be anaplastic oligodendroglioma, GIII. At first I was really happy that it was not GBM after all but after reading more into the results, I'm a bit lost.

Namely, they also said "1p/19q codeletion present; 1p36 / 19q13 codeletion present; in the studied material, a deletion of region 1p36 [75/200], 37.5% and a deletion of region 19q13 [82/200], 41% were observed" (my translation so prone to weird constructions) while they also gave us an immunohistochemistry report which stated "IDH-1 marker result: (-)" which I guess means negative?

So from what I've been able to find, the 1p/19q codeletion is great news and a good prognostic factor. The IDH-1 "(-)" thing (if that means negative) though, seems to indicate the "wild type", faster growing tumors and prognoses similar to GBM. At the same time, most of the reliable sources I found seem to clearly indicate that "The IDH mutation rate in 1p/19q codeleted tumors approaches 100 %" ([source]) or even that " Virtually, all 1p/19q co-deleted oligodendrogliomas have mutation in isocitrate dehydrogenase 1 (IDH1) at arginine 132 (R132) or the analogous residue arginine 172 in IDH2 (R172)" ([source]).

Which leaves me a bit lost... If 1p/19q codeletion means that the IDH mutation is basically a given, does that mean my grandpa falls into the slim, zero-point-something-percent chance of IDH _not_ being present despite the codeletion or does the "(-)" mean something different, or does that coincide with the fact that according to the studies, ~10% IDH mutation tests using immunohistochemistry may be missed (same source as above)? Thanks in advance for helping me figure this out! :)