More detailed EGFR test than cobas? - 1270176

hattrick
Posts:5

Hi,

12 months ago my dad was diagnosed with stage 4 metastatic adenocarcinoma of the lung. He has bone lesions, but no liver, brain or other metastases detected. He's been on a combination of paclitaxel+ gemcitabine+bevacizumab for the past year and, based on PET scans, it seems to be keeping him stable and holding back progression. In fact the main tumor and some of the bone metastases initially shrank somewhat.

He had the cobas EGFR mutation test, and the report just said "Exon 20 insertion detected." It didn't name which of the insertions that test can detect it was. Does this test reveal more specifics about the insertion, and the pathology lab were just being brief in the report, or is "exon 20 insertion detected" truly all the information that test can reveal?

If the latter, are there other EGFR tests that can give more details? Or detect other types of insertion than the 5 insertions the cobas test detects?

Thanks in advance for any help!
- Ben

PS I know that information isn't currently actionable, in that an exon 20 insertion doesn't indicate response to erlotinib/gefitinib. And so far so good on his current chemo regimen anyway. But we'd like to know as much as possible, in case new targeted treatments open up in the future.

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Reply # - June 19, 2015, 07:39 AM

JimC
Posts: 2753

Hi Ben,

Welcome to GRACE. It's good to hear that your dad is responding well to treatment.

The cobas EGFR test can detect:

"41 mutations in exons 18 to 21 of the EGFR‑TK gene:

G719X (G719S/G719A/G719C) in exon 18

29 deletions and complex mutations in exon 19

T790M in exon 20

S768I in exon 20

5 insertions in exon 20

L858R in exon 21 (2 variants)"

according to information provided by the National Institute for Health and Care Excellence in Great Britain here.

In comparison testing with other test methods, the cobas test performed reliably:

http://www.ncbi.nlm.nih.gov/pubmed/23386666
http://www.ncbi.nlm.nih.gov/pubmed/24439568

For a great overview of EGFR mutations, Dr. Pennell wrote a very thorough post here.In the chart in that post, you'll see that there are a couple of uncommon exon 20 deletions which confer EGFR TKI sensitivity.

I think it's a pretty fair guess that the report was just a brief statement of the ultimate results.

Continued good luck with treatment.

JimC
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Reply # - June 19, 2015, 02:21 PM

hattrick
Posts: 5

Thanks for the replies! It seemed odd to me that the test report laboriously listed each of the 41 mutations it can detect, but then didn't say which one it actually did detect, beyond that it was an exon 20 insertion. I can ask the pathology lab if they have more details internally, and I've emailed a couple of other test providers to see if their tests can discriminate a larger range of exon 20 insertions.

Reply # - June 19, 2015, 06:02 PM

sawcmw
Posts: 41

hattrick, My wife has a HER2 mutation with exon 20 insertion. Is it possible you have the same?

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