Molecular variances between rectal and left-sided colon cancers


Mohamed E. Salem, Heinz-Josef Lenz, Joanne Xiu, Wafik S. El-Deiry, Zoran Gatalica, Jimmy J. Hwang, Philip A. Philip, Anthony F. Shields, and John L. Marshall


  • Colorectal cancer (CRC) is a heterogeneous disease with different genetic alterations and clinical behavior
  • CRC was recently classified into four consensus molecular subtypes (CMSs) with distinguishing features1
  • CMS 1-4 tumors have different carcinogenic pathways and genomic patterns
  • Recent retrospective analysis of CALGB 80405 showed that left-sided colon tumors respond differently to biologics compared to right-sided colon tumors1, likely due to molecular differences
  • In the CALGB 80405 analysis, rectal cancers were included as part of the “left-sided” tumors
  • However molecular variations between rectal and left-sided colon tumors are not well defined


  • To identify the molecular variations among left-sided CRC tumors:
    • Rectal cancers
    • Sigmoid colon cancers
    • Descending colon cancers (plus splenic flexure)


  • Retrospective analysis of 1,730 CRC tumors that were profiled by Caris Life Sciences between 2009 and 2016 was performed
  • All samples were independently reviewed by at least one pathologist, in addition to the local pathologist
  • Only primary tumors were included in the current analysis
  • Tumors without clearly defined origins were excluded
  • Chi-square test was used for comparison between groups (IBM SPSS Statistics, Version 23) and significance was defined as p < 0.05


  • Rectal cancers have molecular features that are different from left-sided colon tumors
  • Clinical trials should stratify patients based on the location of the primary tumor (right vs. left) as well as molecular features
  • Better understanding of disease biology may help to identify therapeutic targets and advance precision medicine

Download Publication