Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. Over the last year, Cochrane Neuro-Oncology have been publishing a series of new systematic reviews on priority topics for the brain tumour community. These were selected from the most important unanswered questions identified by patients, the public and practitioners. In this podcast, Kathreena Kurian from the University of Bristol in the UK tells us about one of the reviews, which was published in March 2022, looking at the evidence on some of the tests that might help in planning the treatment of patients with a glioma.

Kathreena: Gliomas are a type of brain tumour. There are different types of glioma, each associated with different changes in their genetic material. One of these genetic changes is the loss of parts of two of a person's 23 chromosomes. These are chromosome 1 and chromosome 19 and when the specific parts are missing, this is known as “1p/19q codeletion” and its detection is used to diagnose a type of glioma known as an oligodendroglioma. Presence of 1p/19q codeletion can also tell us how long a patient with a glioma might survive and which is likely to be the best drug treatment for them. Therefore, we did this review to assess the accuracy and cost-effectiveness of different ways to identify 1p/19q codeletion in gliomas.
We examined and compared a range of methods to detect 1p/19q codeletion that are based on the DNA of the tumour. These include tests known as FISH, CISH, PCR, real time PCR, MLPA, SNP array, CGH array and next generation sequencing. None of these tests is perfect, and there is no 'gold standard' against which to compare them so we used the two most common tests (FISH and PCR) as the best available reference tests against which to examine the others.
We found 53 studies, with a few thousand patients in total and although the evidence was either low or very low certainty, it seems that most tests are good at identifying 1p/19q codeletion (meaning that they have good 'sensitivity') that was also identified by either of the two common tests. However, there were some differences in how good the tests were at ruling out 1p/19q codeletion when it did not seem to be present (the 'specificity' of the test). Next-generation sequencing and SNP arrays were better at this, generating fewer 'false positives' results than the FISH test. The cost per correct diagnosis was lowest for MLPA, although this was not a firm finding because there was so little evidence.
In summary, all the currently used techniques show good sensitivity for detecting 1p/19q co-deletion. Next-generation sequencing and SNP arrays may have higher specificity when FISH is the reference standard, but this comes at greater cost per test.

Mike: For more details about each of the tests, you can read the review online. It's available at Cochrane Library dot com, with a simple search for '1p 19q and glioma'.