Background: Patients with rectal cancer may undergo neoadjuvant chemoradiation even in early stages in an attempt to achieve complete clinical response and undergo organ preservation. However, prediction of tumor response is unavailable. In this setting, accurate identification of poor responders could spare patients with early stage disease from potentially unnecessary chemoradiation.
Objective: This study focused on development/test of a score based on DNA repair gene expression to predict response to neoadjuvant chemoradiation in patients with rectal cancer.
Design: Pretreatment biopsy samples from patients with rectal cancer undergoing neoadjuvant chemoradiation were collected and underwent gene expression analysis using RNA-Seq (test cohort). A score was constructed using 8 differentially expressed DNA repair genes between good (complete clinical) and poor responders (incomplete clinical) to treatment. The score was validated in 2 independent cohorts of patients undergoing similar treatment strategies and using quantitative polymerase chain reaction and microarray gene expression data.
Settings: This was a retrospective analysis of gene expression data from 3 independent institutions.
Patients: Patients with rectal cancer undergoing neoadjuvant chemoradiation (50.4-54.0 Gy and 5-fluorouracil-based chemotherapy) were eligible. Patients with complete clinical response, complete pathological response, or ≤10% residual cancer cells were considered good responders. Patients with >10% residual cancer cells were considered poor responders. The test cohort included 25 patients (16 poor responders). Validation cohort 1 included 28 patients (18 poor responders), and validation cohort 2 included 46 patients (22 poor responders).
Main outcomes measures: Response was correlated with the DNA repair score calculated using the expression levels of 8 DNA repair genes. DNA repair score sensitivity, specificity, and positive and negative predictive values were determined in test and validation cohorts.
Results: Poor responders had significantly lower DNA repair scores when compared with good responders across all 3 cohorts, regardless of the gene expression platform used. A low score correctly predicted poor response in 93%, 90%, and 71% in test, validation 1, and validation 2 cohorts.
Limitations: This study was limited by its small sample size, different gene expression platforms, and treatment regimens across different cohorts used.
Conclusions: A DNA repair gene score may predict patients likely to have poor response to chemoradiation. This score may be a relevant tool to be investigated in future studies focused on chemoradiation used in the context of organ preservation.