What Is ctDNA Testing

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∟What Is ctDNA Testing

Provides a quick introduction on ctDNA testing, which uses blood samples to detect ctDNA fragments to diagnose and monitor tumors.

What Is ctDNA Testing? - ctDNA (circulating tumor DNA) testing uses blood samples to detect ctDNA fragments to diagnose and monitor tumors. ctDNA are DNA fragments released to bloodstream from broken down tumor cells. ctDNA are usually small fragments comprising fewer than 200 nucleotides in length.

Normally, tumor (mutated) DNA is hiding inside chromosome pair, which is protected inside cell's nucleus. You should not see any tumor DNA fragments circulating in bloodstream outside cells.

So we have 2 different ways to perform tumor DNA test:

Tumor Biopsy - Extracting DNA from a tumor tissue sample.
Liquid Biopsy - Extracting ctDNA from a blood plasma samples.

Here are some ctDNA test report examples:

"TruSightTMOncology 500 ctDNA" Example

Disease: Control sample
Specimen Type: Deoxyribonucleic acid sample
Report Date: 02/23/2021

Tier I - Strong Clinical Significance
  No variants

Tier II - Potential Clinical Significance

Gene    Protein Alt    DNA Alt          GenBank ID        VAF  Depth
-----   -------------- ---------------- --------------  -----  -----
CSF3R   p.S469Afs*22   c.1404delC       NM_156039.3      5.5%  2632
NRAS    p.Q61K         c.181C>A         NM_002524.4     12.3%  2392
MLH1    p.S252*        c.755C>A         NM_000249.3     18.5%  2418
CTNNB1  p.S33Y         c.98C>A          NM_001098209.1  31.1%  3071
GATA2   p.G200Vfs*18   c.599delG        NM_032638.4      9.1%  3951
PIK3CA  p.E545K        c.1633G>A        NM_006218.2      8.4%  2676
PIK3CA  p.H1047R       c.3140A>G        NM_006218.2     16.4%  3072
KIT     p.D816V        c.2447A>T        NM_000222.2      8.5%  2958
TET2    p.L1329M       c.3985C>A        NM_001127208.2  25.8%  1856
SDHA                   c.1794+119delA   NM_004168.2     38.2%  3478
EGFR    p.G719S        c.2155G>A        NM_005228.3     23.4%  3850
EGFR    p.E746_A750del c.2235_2249del15 NM_005228.3      1.3%  4866
EGFR    p.T790M        c.2369C>T        NM_005228.3      0.8%  5813
EGFR    p.L858R        c.2573T>G        NM_005228.3      2.3%  5355
BRAF    p.V660E        c.1799T>A        NM_004333.4      9.6%  4030
EZH2    p.G395Efs*19   c.1184delG       NM_004456.4     22.4%  4819
PTCH1   p.S1203Afs*52  c.3606delC       NM_000264.3     28.6%  3713
ATM     p.R1973Efs*17  c.5917delA       NM_000051.3     11.2%  1436
KRAS    p.G13D         c.38G>A          NM_033360.2     14.0%  2526
KRAS    p.G12D         c.35G>A          NM_033360.2      5.3%  2533
BRCA2   p.K1691Nfs*15  c.5073delA       NM_000059.3     31.7%  2118
BRCA2   p.N1784Tfs*7   c.5351delA       NM_000059.3     35.5%  1989
BRCA2   p.I2675Dfs*6   c.8021dupA       NM_000059.3      8.2%  2451
BRCA1   p.R1443*       c.432C>T         NM_007300.3     26.6%  3302
SMARCA4 p.S122Lfs*7    c.363dupC        NM_001128849.1  11.0%  2625
RUNX1   p.M267I        c.801G>A         NM_001754.4      9.2%  4046
BCOR    pQ1208Tfs*8    c.3621dupA       NM_001123385.1  13.7%  1662

"Liquid Biopsy, ctDBA, EGFR" Example

Test Conducted: Liquid Biopsy, cell free DNA, EGFR mutation analysis
Indication & Sample: Liquid Biopsy, Plasma separated from Streck tube
Report Date: 10/08/2020  

Mutations analyzed in sample:

EGFR Exon 19 deletion   EGFR Exon 20           EGFR Exon 21
E746_A750del            Point Mutation T790M   Point Mutation L858R
---------------------   --------------------   --------------------
Not Detected            Not Detected           Not Detected