Molecular diagnosis of response to neoadjuvant chemoradiation therapy in patients with locally advanced rectal cancer

Abstract

Background: Pathologic complete response (pCR) to neoadjuvant chemoradiation (CRT) is an important prognostic factor in locally advanced rectal cancer. However, it is uncertain if histopathological techniques accurately detect pCR. We tested a novel molecular approach for detecting pCR and compared it with current histopathological approaches.

Study design: Pretreatment tumor biopsies and surgical specimens were collected from 96 patients with locally advanced rectal cancer treated with neoadjuvant CRT and surgery. Tumor response was categorized by tumor regression grade. Tumor DNA from pre-CRT tumor biopsies was screened for K-ras and p53 mutations. DNA from paired surgical specimens was then screened for the same mutations using highly sensitive polymerase chain reaction-based techniques.

Results: Sixty-eight of 96 (71%) pretreatment biopsies harbored K-ras and/or p53 mutation; 36 (38%) had K-ras mutations, 52 (54%) had p53 mutations, and 20 (21%) carried both mutations. Of 70 patients with tumor regression grades 1 to 3, sixty-six (94%) had a concordant K-ras and p53 mutation profile in pre- and post-treatment tissues. Of 26 patients with tumor regression grade 0 (pCR), 12 had K-ras or p53 mutations in pretreatment biopsies. Of these, 2 (17%) patients had the same K-ras (n = 1) or p53 (n = 1) mutation detected in post-treatment tissue.

Conclusions: Sensitive molecular techniques detect K-ras and p53 mutations in post-CRT surgical specimens in some patients with a pCR. This suggests histopathological techniques might not be completely accurate, and some patients diagnosed with a pCR to CRT might have occult cancers cells in their surgical specimens.

Trial registration: ClinicalTrials.gov NCT00335816.

Copyright © 2011 American College of Surgeons. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

Mutation analysis of pre-and post treatment patient specimens. (a): One patient (TRG 1) had a discordant K-ras mutation profile pre-and post treatment. The mutation is within codon 12. The upper panel shows K-ras mutation in the first position of codon 12 (GGT > AGT) in the pre-treatment biopsy specimen. The lower panel shows K-ras mutation in the second position of codon 12 (GGT>GAT) in the surgical specimen following treatment. (b): One patient (TRG 3) harbored a new p53 mutation in the surgical specimen that was not present in the pre-treatment biopsy. The upper panel shows a wild-type genotype following sequencing exon 6 of the p53 gene in the pre-treatment biopsy. The lower panel shows a new mutation in codon 195 of exon 6 (ATC > AAC) in the surgical specimen following treatment. (c): One patient who was TRG 0 after treatment had a mutation in the K-ras gene. The upper panel shows mutation in codon 12 GGC > GAC of the K-ras gene in the pre-treatment biopsy specimen. The lower panel shows the same mutation in codon 12 GGC > GAC in the surgical sample detected by PNA clamp PCR.