There has been a high local recurrence rate in rectal cancer. Besides improvements in surgical techniques, both neoadjuvant short-course radiotherapy and long-course chemoradiation improve oncological results. Approximately 40–60% of rectal cancer patients treated with neoadjuvant chemoradiation achieve some degree of pathologic response. However, there is no effective method of predicting which patients will respond to neoadjuvant treatment. Recent studies have evaluated the potential of genetic biomarkers to predict outcome in locally advanced rectal adenocarcinoma treated with neoadjuvant chemoradiation. The articles produced by the PubMed search were reviewed for those specifically addressing a genetic profile’s ability to predict response to neoadjuvant treatment in rectal cancer. Although tissue gene microarray profiling has led to promising data in cancer, to date, none of the identified signatures or molecular markers in locally advanced rectal cancer has been successfully validated as a diagnostic or prognostic tool applicable to routine clinical practice.
Colorectal cancer is the third most frequent cancer and the second most frequent cause of cancer related death, both in Europe [
An exhaustive search of PubMed was performed on March, 2014, with combinations of the following terms: “rectal cancer,” “response,” “prediction,” “microarray,” “gene expression,” “mi-RNA,” and “ln- RNA.” The articles produced by the PubMed search were reviewed for those specifically addressing a genetic profile’s ability to predict response to neoadjuvant CRT in LARC (genes, microRNA, or long noncoding RNA). Articles analysing response prediction to CRT in colorectal cancer cell lines were excluded. Sixteen studies evaluating genetic profiles predicting outcome of neoadjuvant CRT in rectal cancer were found. Ten of them identified an over- or downregulated gene signature, 5 found microRNA (miRNA) signature. Only one screened long noncoding RNA (lncRNA) was associated with radiosensitivity but was made in colorectal cancer cell lines and was written in Chinese and therefore was excluded.
The first study on the application of a genetic signature to predict response to neoadjuvant treatment in rectal cancer appeared in 2005 [
Studies showing DNA microarray gene expression profile predictive of response to CRT in LARC.
Study | Specimen |
|
Validation group |
|
Response assessment | Identified genes: more relevant genes | Outcome |
---|---|---|---|---|---|---|---|
Ghadimi et al. 2005 [ |
Tumor tissue biopsy | 30 | No |
|
|
54 genes: SMC1, CLMN, CDC42BPA, and FLNB | Group prediction 83% |
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Watanabe et al. 2006 [ |
Tumor tissue biopsy | 52 | 17 |
|
Japanese Classification of Colorectal Carcinoma | 33 genes |
Class prediction 82.4%, |
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Kim et al. 2007 [ |
Tumor tissue biopsy | 31 | 15 |
|
Dworak regression grade | 95 genes: TYMS and RAD23B | Precision 87%, |
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Rimkus et al. 2008 [ |
Tumor tissue biopsy | 43 | No |
|
Becker regression grade | 42 genes |
Accuracy 81%, |
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Nishioka et al. 2011 [ |
Tumor tissue biopsy | 17 | 3 |
|
Japanese Classification of Colorectal Carcinoma | 17 genes: MMP7, MMP14, MMP9, MMP1, MMP16, and RRM1 | |
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Casado et al. 2011 [ |
Tumor tissue biopsy |
25 |
|
Dworak regression grade | 24 genes: genetic profile of 13: |
Nonresponders: | |
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Palma et al. 2013 [ |
Blood sample | 27 | 8 |
|
Mandard regression grade | 8 genes: FALZ | |
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Palma et al. 2014 [ |
Tumor tissue biopsy | 26 | 8 |
|
Mandard regression grade | 257 genes: c-MYC, GNG4, POLA, and RRM1 | Accuracy 85%, |
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Gantt et al. 2014 [ |
Tumor tissue biopsy | 36 | 10 |
|
American Joint Committee on Cancer | 183 genes up- and downregulated: RAD50 | No response: |
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Watanabe et al. 2014 [ |
Tumor tissue biopsy | 46 | 16 |
|
Japanese Classification of Colorectal Carcinoma | 22 probes (18 genes): signature LRRIQ3, FRMD3, SAMD5, and TMC7 | Accuracy 81.3%, |
The following year a Japanese group with a similar objective, published a
Kim and colleagues conducted a study in 2007 using samples from 46 patients (31 for the initial trial group and 15 for the validation) [
Rimkus et al. [
More recently, a group formed by Nishioka and colleagues [
Our group [
Granttet published a study in 2014 using high-throughput nucleotide
Recently, Watanabe conducted a new study to establish a prediction model for response to chemoradiotherapy in rectal cancer based on gene expression by RT-PCR analysis as it allows accurate and reproducible quantification of genes [
Peripheral blood mononuclear cells have emerged recently as pathology markers of cancer and other diseases, making their use as therapy predictors possible. Furthermore, the importance of the immune response in radiosensitivity of solid organs led Palma et al. [
MicroRNAs (miRNAs), discovered in 1993, represent a relatively new field in the rapidly developing world of genetics and the regulation of genetic expression. A miRNA is a small sequence of single-stranded RNA (normally between 18 and 25 nucleotides) that do not code proteins but do act as posttranscriptional regulators of genetic expression. They act by binding to complementary strands of messenger RNA, usually inhibiting expression and silencing the gene. Their function can be very similar to the function of oncogenes as well as tumor-suppressing genes [
Studies showing miRNA expression profile predictive of response to CRT in LARC.
Study | Specimen |
|
Validation group |
|
Response assessment | Identified miRNA: more relevant miRNAs | Outcome |
---|---|---|---|---|---|---|---|
Svoboda et al. |
Tumor tissue biopsies | 35 |
|
Dworak regression grade | Interpatient variability |
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Della Vittoria Scarpati et al. 2012 [ |
Tumor tissue biopsy | 35 |
|
Mandard regression grade | 57 miRNAs: 13 confirmed by PCR |
Sensitivity 100% | |
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Kheirelseid et al. 2013 [ |
Formalin-fixed paraffin-embedded |
12 |
|
Mandard regression grade | Downregulated: miR-10b, miR-143, and miR-145 |
Accuracy 100% | |
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Svoboda et al. 2012 [ |
Tumor tissue biopsy | 20 |
|
Mandard regression grade | Nonresponders: |
Accuracy 90% | |
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Hotchi et al. 2013 [ |
Tumor tissue biopsy | 43 | 21 |
|
Histopathological |
2 miRNAs: miR-223 |
AUC 0.768 |
Changes in miRNA expression can be induced as a consequence of various external stimuli such as hypoxia and gemcitabine. Svoboda and colleagues studied changes of selected microRNAs in rectal cancer biopsies from patients treated with chemoradiotherapy (50.4 Gy in 1.8 fractions concomitantly with capecitabine) and correlation with response [
In 2012 Della Vittoria Scarpati and colleagues published an article based on this technique which established a specific profile associated with response to treatment in the biopsies of patients with locally advanced rectal neoplasms who underwent neoadjuvant therapy [
The authors of another recently published study [
In another retrospective study large-scale miRNA expression analysis was performed on 20 samples of preoperative biopsies of rectal cancer tissues [
Hotchi’s group from Japan obtained rectal cancer samples during colonoscopy from 43 patients, prior to preoperative chemoradiotherapy (22 for training and 21 for testing the outcome prediction model) [ Histopathological examination of surgically resected specimens (based on a semiquantitative classification system). Tumors were classified as responders when assigned to regression grade 2 or grade 3 and nonresponders when assigned to grade 0 or grade 1. Response Evaluation Criteria in Solid Tumors (RECIST): tumors were classified as responders when assigned to complete response (CR) or partial response (PR) and nonresponders when stable disease (SD) or progressive disease (PD) was reported. Downstaging (yes/no): using real-time RT-PCR in a training set, a candidate miRNA detected by miRNA microarray analysis was evaluated.
With regard to the histopathological examination of surgically resected specimens, two genes are differentially expressed at significant levels in responders and nonresponders (miR-223 and miR-142-3p), with responders showing higher expression in comparison to nonresponders. Nine genes were differentially expressed at significant levels with regard to RECIST: one (miR-223) showed a higher expression, while eight showed a lower expression (miR-20b, miR-92a, let-
In 2011 Casado and colleagues performed a serial analysis of genetic expression to identify a genetic profile that could predict response to chemoradiation therapy in locally advanced rectal cancer [
Currently, a multicentric study backed by the
There has been a high local recurrence rate in LARC. Besides improvements in surgical techniques, both neoadjuvant short-course radiotherapy and long-course chemoradiation improve oncological results [
Modern oncological treatment decisions increasingly depend on so-called clinical and laboratory predictive and prognostic markers. While prognostic markers explain variability irrespective of treatment, our study intends to use predictive markers to explain outcome variability in response to treatment. Gene expression profile using the microarray technology has led to a series of promising results through tissue gene expression profiling of different malignancies, including cancer. Interestingly, gene signatures have been used successfully as prognostic predictor for patients with colorectal carcinomas [
A successful biomarker should be able to predict a certain group of rectal cancer patients that would be likely to experience response or even a pCR. For this group of patients, the biomarker would be a useful prognostic factor that could indicate a more favorable outcome, and their management would not change from the standard treatment regimen. Those patients with biomarkers predicting a poor response to standard treatment could be offered adjusted therapy courses in terms of the agents used or sequence of treatments (e.g., induction chemotherapy, the addition of a targeted agent such as an EGFR antibody, or surgery without any delay, followed by adjuvant CRT).
The literature was reviewed for studies of biomarkers predicting response to neoadjuvant CRT for rectal cancer. Fifteen studies evaluating genetic profiles predicting outcome of neoadjuvant CRT in rectal cancer were analyzed. Ten of them identified an over- or downregulated gene signature; five studies found microRNA (miRNA) signature.
Although tissue gene microarray profiling has led to promising data in cancer, to date, none of the identified signatures or molecular markers in LARC has been successfully validated as a diagnostic or prognostic tool applicable to routine clinical practice. Moreover, there has been little agreement between signatures published, with scarce overlap in the reported genes [
Significant bias was found by analyzing the literature. The scant number of patients in the studies is one of them. The evaluated studies examined between 12 and 94 patients. Even if a significant correlation was determined between a biomarker and a measurement of outcome, the literature has failed to demonstrate reproducibility. Before the clinical use can be established, prospective studies, including a large number of patients should be performed in order to achieve reproducible results.
Furthermore, significant variability in the CRT course can hinder the interpretation of results. Neoadjuvant CRT for LARC typically consists of 5FU and 45–50.4 Gy of pelvic irradiation. By using alternative chemotherapeutic agents in the studies, the results are more difficult to interpret. For example, the addition of oxaliplatin or irinotecan to 5FU for a subset of patients could confound the outcome measurements by altering the baseline response. Variability in the response scoring system is also a debatable bias between the studies.
Despite this variability, our review underlines two main hypothesis: first, the elevated expression of c-Myc mRNA as an important marker of response to CRT in LARC as an essential component of the neoplastic phenotype in rectal tumors.
Second, miRNAs, highly conserved noncoding RNAs ranging between 21 and 24 nucleotides in size, play a major role in the posttranscriptional regulation of mRNA. The inhibition of translation after forming a complex similar to the RNA-interference-induced silencing complex (RISC), by downregulating the expression of their protein-coding gene targets, is the general mechanism of microRNA action in animal and human cells [
In conclusion, the current literature does not lend enough support to any of the biomarkers to permit the clinical application in order to predict outcome to neoadjuvant CRT in rectal cancer.
In future clinical trials, assessing neoadjuvant CRT for rectal cancer, these biomarkers should be prospectively evaluated to determine their role as predictors of outcome. It is clear that there is a biological basis as to why some tumors respond to CRT and that biology could be related to the tumor, the patient, or both. In this context, the genes identified in Mononuclear Peripheral Blood Cells could offer new insights into the immune system’s dysregulation in LARC [
The authors declare that there is no conflict of interests regarding the publication of this paper.