mCRC: Next-Generation Sequencing vs Other Testing


Wells Messersmith, MD:In terms of next-generation sequencing, that’s what most of the panels, including in the community, have turned to. There are PCR-based tests where basically you amplify the DNA specifically around certain codons and you’re looking for very specific mutations. But more and more now, people are turning to next-generation sequencing where you’re going to pick up more of these rare mutations and also other alterations. And so, nowadays, most people are catching a much broader net. The biggest mistake I see when people don’t do NGS testing is that they’re only testing for codon 12 and 13 ofKRAS, and if you do that, you’re going to miss all yourNRASmutations, plus you’re going to missKRASmutations in other codons. And as far we know now, those mutations should be lumped, and so you don’t want to basically miss that. By testing other mutations, you’re going to pick up, depending on the trial you look at, 15% to 20% of other mutations.

And remember, we’re not talking about just wasting money in terms of giving a drug to someone that’s not going to benefit. Some trials have shown harm in patients who have anNRASor aKRASmutation who receive those drugs. You’re not only wasting resources and causing toxicity, but you’re also harming the patient. So, it’s important to keep that in mind. BRAF testing, again, can be either with NGS or a specific test if both are available. But rather than testing a bunch of individual things, what we’re finding is NGS testing—where you’re catching a wider net—you’re just sequencing the whole gene and we’re just picking up more of these rare mutations. And so, there’s a little bit more comfort with the fact we’re not missing things.

In terms of an academic versus a community setting, I think those differences are becoming less and less now. Most of the academic centers, including at University of Colorado, we have our own in-house test. The advantage of that is just that we can get the results very quickly, within 24 to 72 hours. In the community, you’re often sending those tests out. It takes a little longer, although with most of the testing nowadays, the turnaround time is fairly quick. So, actually, I feel like the community testing and the academic testing are becoming more and more similar as time goes on. And there are well-known testing companies that many of the community folks are sending their samples to anyway, which are also often used by academic centers. So, honestly, the differences between the 2 is less. The main mistake I see is not checking those other mutations.

The differences between academic molecular testing and community molecular testing are becoming less and less. And more and more community physicians are sending NGS testing, or next-generation sequencing testing, for these workups. From my point of view, one of the main things to avoid are specific colon panels that don’t have other codons inKRAS, aside from 12 and 13, and don’t haveNRAS. And I had to have a conversation with our molecular pathologists to not do those testings. We call it “molecular malpractice” because if you send that, the physician is going to have a false sense of reassurance that it’s a wild-type, nonmutated patient when, in fact, they might be mutated. It’s hard to keep up with these things. The nice thing about NGS, though, is because you are casting a wider net, you’re going to get more information.

Transcript edited for clarity.

September 2015

  • A 71-year-old Caucasian male presented with severe left lower quadrant pain
    • He sought medical treatment after experiencing bloody diarrhea
  • PMH: hypertension, managed with benazepril
  • He is active and can perform daily activities without restrictions
  • Laboratory findings: remarkable for CEA, 6.0 ng/mL
  • Colonoscopy showed a mass in the descending colon which was biopsied
    • Pathological findings: Moderately differentiated adenocarcinoma
  • NGS mutation testing results wereNRAS, KRAS, HRAS, HER2,andBRAFwild-type
    • Microsatellite stable
  • CT of the chest, abdominal, and pelvis showed an 8-cm mass in the sigmoid colon
    • a 2-cm mass in the right lobe of the liver, and a 5-cm in the left lobe adjacent to the left hepatic vein
    • Impression: metastatic disease, borderline resectable
  • Treatment was initiated with FOLFIRI + bevacizumab
  • Imaging at 3 and 6 months showed decreased size of the liver nodules, but was not resectable

July 2016

  • The patient complained of increased fatigue, requiring the need for frequent rest
  • CT scan showed increasing size of the liver nodule (3 cm) and appearance of 3 new small liver lesions (<2 cm)
  • He began therapy with FOLFOX + bevacizumab

February 2017

  • The patient reported weight loss, increasing fatigue, and shortness of breath
  • CT scan revealed progressive disease with no improvement in the primary and metastatic lesion size and/or number
  • A new pulmonary nodule was seen in the right lung
  • He was switched to irinotecan + cetuximab
  • PET/CT at 3 months showed stable disease
  • At 6 months, he reported moderate improvement in fatigue
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