KRAS mutational analysis (MA) in plasma (P) cfDNA is an alternative to tissue (T) analysis with concordance rate (ConR) from 30 to 90%. The emergence of KRAS mutation (M) during the course of anti-EGFR therapy is responsible for acquired resistance (AR). We aimed to evaluate the RAS ConR between T and cfDNA in mCRC pts, and to monitor changes in RAS M status.
All blood samples were collected in cfDNA Preservative Tubes (Norgen Biotek Corp., Canada). ctDNA was extracted within 3 days after sampling, the extraction was performed by commercial kit (P/Serum cfDNA Purification Mini Kit, Norgen Biotek). KRAS (ex 2) M on P cfDNA and tumor T were detected by real-time PCR kits TheraScreen: K-RAS Mutation Kit. The other M were detected by Sanger sequencing (BigDye Terminator v3.1 Cycle Sequencing Kit - Thermo Fisher Scientific).
In the ConR evaluation were enrolled prospectively 63 mCRC pts. Only LM had 52,4% (33) pts, from whom - 27,3% (9) pts had primary resectable LM. The median time from T biopsy (primary -97%) to P collection was 275, 7 days (range 26 - 1560). TMA revealed 58,7% (37) M pts from whom 78,4% (29) pts had KRAS ex.2 M. cfDNA evaluation showed the distribution of M to wild (W) - 81%/19% with KRAS ConR of 58,7%. To reduce time between T and P samples MA in the monitoring analysis were included only 31 pts who had primary unresectable LM, with baseline (b) P collection. In 5 pts with KRAS M after converting treatment, LM resection resulted in W type on consecutive cfDNAs. In responding pts (10) with W disease on bcfDNA, there was no change in MA consequently. In non-responders with W type the appearance of KRAS M was noted in 6 pts, while in the rest 3 pts PD was not correlated to KRAS M. In non-responders with KRAS M on bcfDNA (6 pts), monitoring of cfDNA revealed disappearance of KRAS M contemporary with mainly LM PD.
The estimated ConR between primary tumor and cfDNA KRAS MA was 58%. The emergence of KRAS M in W type pts reveled AR to anti-EGFR therapy. In pts with M KRAS on bcfDNA, liver resection in responders and LM PD in non-responders correlated with loss of KRAS M as a mechanism of AR to anti-angiogenesis treatment in the later.
Clinical trial identification
Legal entity responsible for the study
Prof. Albena Parvanova Todorova-Georgieva.
Medical University Sofia.
All authors have declared no conflicts of interest.