Abstract
Objectives
Among the most important diagnostic indicators of colorectal cancer; however, measuring molecular alterations are invasive and expensive. This study aimed to investigate the application of image processing to predict molecular alterations in colorectal cancer.
Methods
In this scoping review, we searched for relevant literature by searching the Web of Science, Scopus, and PubMed databases. The method of selecting the articles and reporting the findings was according to the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses; moreover, the Strengthening the Reporting of Observational Studies in Epidemiology checklist was used to assess the quality of the studies.
Results
Sixty seven out of 2,223 articles, 67 were relevant to the aim of the study, and finally 41 studies with sufficient quality were reviewed. The prediction of Kirsten Rat Sarcoma Viral Oncogene Homolog (KRAS), Neuroblastoma RAS Viral (NRAS), B-Raf proto-oncogene, serine/threonine kinase (BRAF), Tumor Protein 53 (TP53), Adenomatous Polyposis Coli, and microsatellite instability (MSI) with the help of image analysis has received more attention than other molecular characteristics. The studies used computed tomography (CT), magnetic resonance imaging (MRI), and 18F-FDG positron emission tomography (PET)/CT with radionics and quantitative analysis to predict molecular alterations in colorectal cancer, analyzing features like texture, maximum standard uptake value, and MTV using various statistical methods. In 39 studies, there was a significant relationship between the features extracted from these images and molecular alterations. Different modalities were used to measure the area under the receiver operating characteristic curve for predicting the alterations in KRAS, MSI, BRAF, and TP53, with an average of 78, 81, 80 and 71%, respectively.
Conclusion
This scoping review underscores the potential of radiogenomics in predicting molecular alterations in colorectal cancer through non-invasive imaging modalities, like CT, MRI, and 18F-FDG PET/CT. The analysis of 41 studies showed the appropriate prediction of key alterations, such as KRAS, NRAS, BRAF, TP53, and MSI, highlighting the promise of radionics and texture features in enhancing predictive accuracy.
Introduction
Colorectal cancer is the third most common cancer in the world; it ranks second in men and third in women in terms of cancer-related deaths (1, 2). In 2022, a total of 1,926,118 new cancer cases and 903,859 deaths were reported (3). Although the incidence of cancer has decreased in high-income countries because of continuous screenings in the elderly and changes in risk factors (1, 4), it is still increasing in low-income countries (5, 6).
Colorectal cancer, which is caused by the accumulation of genetic and epigenetic changes in the colon epithelium, is a complex heterogeneous disease with different histopathology, (7). These changes lead to the activation of oncogenes, inactivation of tumor suppressor genes, and disturbance in the regulation of signaling pathways involved in cell proliferation, differentiation, and apoptosis (8). As a result of different histopathology and heterogeneity, the progress of colorectal cancer is very different in different people. Therefore, it is very important to predict disease progression to determine the appropriate treatment (7). To date, many efforts have been made to identify factors affecting disease progression, such as the “Tumor”, “Nodes”, “Metastases” (TNM) classification which, from histopathology point of view, classifies cancer into four groups with different rates of disease progression (9, 10). However, the rate of disease progression in the TNM groups differed due to the molecular differentiation and heterogeneity within the tumor (11).
One-way to predict disease progression is to pay attention to molecular alterations, such as Kirsten Rat Sarcoma Viral Oncogene Homolog (KRAS), Neuroblastoma RAS Viral (NRAS), B-Raf proto-oncogene, serine/threonine kinase (BRAF), Tumor Protein 53 (TP53), microsatellite instability (MSI) and PIK3CA (9). Current methods for measuring these factors in colorectal cancer, such as DNA sequence analysis, are costly, time-consuming, and invasive (12). In addition, sampling from one point of the tumor to perform genetic tests and heterogeneity in different parts of the tumor, this method may not accurately reflect the molecular alterations of colorectal cancer (13). The problems of measuring molecular alterations can be overcome by predicting their values through analyzing medical images, such as computed tomography (CT) scan, magnetic resonance imaging (MRI), and 18F-FDG PET/CT, which have recently attracted the attention of researchers (12). Radiogenomics, a new concept introduced in recent years, examines the relationship between molecular alterations (especially genetic alterations) of cells and images (9). Non-invasive imaging provides information on tumor morphology and metabolism to some extent and can be used to identify potential biomarkers and molecular alterations in colorectal cancer (12). Several studies have shown that CT scanning can predict the KRAS mutation status in colorectal cancer patients (14, 15).
However, the use of image processing to predict MC molecular alterations is still in its early stages (12, 16). Therefore, this study aimed to investigate the use of image processing to predict molecular alterations in colorectal cancer. The research questions of this study are as follows:
1. Which molecular alterations have received more attention in the field of radiogenomics?
2. Which imaging modalities are used to predict molecular alterations?
3. What is the performances of the modalities in the prediction of various molecular alterations?
Materials and Methods
In this scoping review conducted in 2024, the reporting process was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) (17). All original articles published from January 01, 2013 to April 31, 2024 and indexed in Scopus, PubMed, and Web of Science databases were extracted. The inclusion criteria were original research articles in colorectal cancer. The exclusion criteria were review studies, non-English articles, studies beyond the scope of colorectal cancer, and articles with limited access.
The standard keywords and their synonyms for the three terms “molecular alterations”, “medical image” and “colorectal cancer” were determined according to medical subject headings, and a search strategy was determined for each database (Table 1, 2).
After searching and retrieving sources based on the search strategies, duplicate articles were removed using EndNote software. Then, the titles and abstracts of the articles were checked, and irrelevant articles were removed. This screening was performed by two experts in the field of Medical Informatics, and any disagreement was resolved by consensus with a third expert. In the next step, the full texts of the articles were reviewed. Finally, articles that were in line with the purpose of the study were selected. The quality of the selected articles was measured using the Strengthening the Reporting of Observational Studies in Epidemiology checklist, and articles with insufficient quality were excluded from the study (18).
The data collection tool consisted of a data extraction form including the type of study, first author’s name, country and year of publication, purpose of the study, sample size, molecular factors, type of modality, image characteristics, statistical method for prediction, and summary of findings. Furthermore, a narrative synthesis method was used for data analysis.
Statistical Analysis
In this study, basic descriptive statistics, including the sum and mean, were used to analyze the results. Additionally, when the area under the ROC curve was calculated to predict molecular alterations in the studies, the weighted average was computed based on the molecular alterations and modality.
Patient Consent Information
This systematic review was based on data from previously published studies, and new patient data were not collected. Therefore, patient consent was not required.
Results
A summary of the study review process based on the PRISMA guidelines is presented in Figure 1.
Molecular Factors
Research has shown that many molecular factors contribute to the treatment of colorectal cancer. Some of the key molecular factors (genes/oncogene/suppressor) in colorectal cancer are KRAS, BRAF, NRAS, PIK3CA, and TP53 (9). Various molecular factors were predicted in the selected studies; however, in 68% of them, KRAS changes were investigated. The frequency of the investigated molecular factors is shown in Figure 2.
Modalities
Recently, different imaging modalities have been used for predicting molecular factors in colorectal cancer. The most important modalities are MRI, CT, and positron emission tomography (PET) (9). The frequency of modalities used in the included studies is presented in Figure 3.
Analyzing Technics
The reviewed studies employed various imaging modalities, such as CT, MRI, and 18F-FDG PET/CT, and utilized radionics and quantitative analysis techniques to predict molecular alterations in colorectal cancer. Key features analyzed included texture features, maximum standardized uptake value (SUVmax), SUVmean, metabolic tumor volume, total lesion glycolysis, and various radionics features derived from intensity, shape, and texture matrices like GLCM, GLRLM, GLSZM, and NGLDM. The statistical methods varied, including Spearman correlation, Mann-Whitney U test, logistic regression, and machine learning models like random forest and SVM.
Area Under the Receiver Operating Characteristic (ROC) Curve for Predicting Molecular Factors Based on Image
In 20 studies, the area under the ROC curve (AUC) was reported for predicting KRAS (n=13), MSI (n=4), BRAF (n=2), and TP53 (n=1) changes. The weighted average of this index (relative to the number of samples) for each molecular factor is presented in Table 3. Table 4 presents the relationships among the three modalities used in studies on molecular factors.
Discussion
In this systematic review, 41 studies related to the use of radiogenomics in colorectal cancer for predicting molecular factors were examined. According to the results, 42% of the studies were conducted in China, and 71% of the studies were conducted between 2019 and 2022. According to recent progress in understanding the relationship between molecular factors and response to drugs, the emergence of the concept of radiogenomics, and the increase in the quality of different modalities in recent years, such studies have received much attention from researchers (9).
Furthermore, most studies have investigated the association between medical images and RAS (KRAS, NRAS), BRAF, TP53, activated protein C (APC), and MSI alterations with a frequency of 35, 28, 8, 7, 5, 4, and 4, in that order. RAS mutations (KRAS/NRAS) are common in colorectal cancer and can affect treatment outcomes. These mutations are associated with resistance to anti-epidermal growth factor receptor monoclonal antibodies and limit their efficacy. Targeted therapies that specifically inhibit mutant KRAS are being developed to overcome this resistance (59, 61). RAS mutations have been investigated in 35 studies, and the relationship between image characteristics and molecular factors was significant in 33 studies. Moreover, 13 studies used image analysis to report the area under the ROC curve for predicting KRAS whose weighted average, relative to the number of samples, was 78%, which is in contrast with the result of the study by Kim et al. (2), where the same value for 9 studies was 69%. This difference can be attributed to the research period. Additionally, regarding recent advances in imaging and image-analyzing methods, the higher level under the ROC curve in the present study can be justified.
BRAF mutations, particularly V600E mutation, are found in a subset of colon cancers and are associated with poor prognosis. In recent years, BRAF inhibitors have shown promise in the treatment of colorectal cancer (with BRAF mutation), either alone or in combination with other drugs (61). BRAF mutation has been examined in 7 studies, and the relationship between image features and BRAF mutation was significant in 6 studies. In 2 studies image analyzing was used to report the area under the ROC curve for predicting BRAF whose weighted average, in relation to the number of samples, was 80%. In their study, Santhanam et al. (62) identified 7 studies on the relationship between 18F-FDG PET/CT characteristics and BRAF mutation in thyroid cancer, and the results indicated a significant relationship between them.
TP53 is a tumor suppressor that plays an important role in maintaining genomic stability. TP53 mutations are frequently found in colorectal cancer, and they are associated with worse prognosis and resistance to therapy. New therapies targeting TP53 mutations (such as gene therapies and small molecule inhibitors) are being investigated to overcome these challenges (63). The TP53 mutation has been investigated in 5 studies where the relationship between image characteristics and TP53 mutation was significant. In another study, image analysis was used, and the area under the receiver operating characteristic curve for predicting TP53 was 71%. In their review study, Seow et al. (64) investigated the relationship between radiomic features and molecular factors and found a correlation between TP53 mutation and radiomic features.
MSI is observed in approximately 15% of colorectal cancers. From the treatment point of view, high MSI colorectal cancers exhibit particular responses to immunotherapy; they respond better to immune checkpoint inhibitors (65). Image analysis was used in 4 studies to report the area under the receiver operating characteristic curve for MSI, with an average of 81%. Similarly, Le et al. (66) identified 8 studies related to the use of radionics for the prediction of MSI, and the average area under the ROC curve was 83%.
As a suppressor, APC plays an important role in the development of colon cancer and is used to identify people at risk or diagnose the disease. In addition, Wnt pathway inhibitors therapies may be appropriate for APC-mutated colorectal cancer (67). APC mutation has been examined in 4 studies in which the relationship between image feature and APC changes was significant. A review study by Aghabozorgi et al. (68), on the relationship between radionics features and histopathological changes indicated a relationship between APC mutation and radionics features.
MRI, CT scanning, and 18F-FDG PET/CT were used in 10, 15, and 16 studies, respectively. MRI is a non-invasive imaging technique that provides high-resolution anatomical images. It provides good soft-tissue contrast and is useful for evaluating colorectal tumor characteristics, such as size, location, and invasion depth (9, 69). According to the performance of MRI, this modality is mostly used for predicting RAS (KRAS/NRAS).
There was also a significant relationship between MRI and molecular factors in all selected studies, except for Horvat et al. (52) study in which qualitative characteristics of images were related to molecular factors; however, no significant relationship was found between quantitative characteristics and molecular factors due to the limitations presented in the study.
The analysis of radionics and quantitative features across various imaging modalities, such as CT, MRI, and 18F-FDG PET/CT, revealed the potential for predicting molecular alterations in colorectal cancer. Radiomics features, including texture and intensity metrics, can help improve the prediction accuracy. Techniques like GLCM, GLRLM, and GLSZM combined with statistical methods such as logistic regression and machine learning models demonstrate varying degrees of success in identifying key genetic mutations such as KRAS, NRAS, BRAF, TP53, and MSI. However, the heterogeneity in methodologies and sample sizes across studies underscores the need for standardized imaging protocols and radiomic analysis techniques.
Study Limitations
Because the studies were conducted considering a small sample size and were still in their early stages, multi-center prospective studies with a larger number of participants should be conducted.
Conclusion
This scoping review highlights the promising potential of radiogenomics in predicting molecular alterations in colorectal cancer through noninvasive imaging modalities. Our comprehensive analysis of 41 high-quality studies revealed that various imaging techniques, including CT scanning, MRI, and 18F-FDG PET/CT, can effectively predict key molecular changes, such as KRAS, NRAS, BRAF, TP53, and MSI. The primary focus has been on CT scanning and MRI, with texture features and radionics playing critical roles in enhancing predictive accuracy. Despite these advancements, the field is still in its nascent stages, with varying levels of predictive performance and sample sizes. The heterogeneity of methodologies and the need for larger, more diverse cohorts underscore the need for further research. Standardization of imaging protocols and radiomic analysis, along with cross-institutional collaborations, will be crucial for validating and refining these predictive models. In conclusion, radiogenomics has significant potential to revolutionize the prediction of molecular alterations in colorectal cancer, facilitating personalized treatment approaches. Continued research and technological advancements are essential for fully realizing its clinical implications and improving patient outcomes.