Synthetic magnetic resonance imaging predicts the prognostic evaluation of rectal cancer
We read with interest the article by Ma et al. (1) published in the journal of Quantitative Imaging in Medicine and Surgery. The authors conducted a prospective, single-centre study involving eighty-seven patients who had pathologically confirmed rectal cancer and underwent synthetic magnetic resonance imaging (SyMRI) before therapy. Ma et al. found that T2 and proton density (PD) values obtained by SyMRI decreased significantly among patients with poor differentiation and lymph node metastasis and concluded that T2 and PD. values were noninvasively prognostic factors of rectal cancer. We appreciate their efforts to provide insights into the noninvasive evaluation of patients with rectal cancer. However, some points merit further discussion.
Firstly, the article included important prognostic indicators such as mrT, mrN stage and tumour differentiation. However, many other critical prognostic factors which surgeons are greatly concerned about were still not included, like mesorectal fascia (MRF) status, lateral lymph node, and histological type. MRF is an essential structure in rectal cancer, defined as the fine linear structure enveloping the mesorectal compartment harbouring the rectum perirectal fat. If it is violated, the further use of total mesorectal excision and neoadjuvant radiotherapy might be needed (2,3). Besides, the incidence of lateral pelvic lymph node metastasis has been estimated to range from 11% to 22% in patients with T3/4 rectal cancer below the peritoneal reflection, which is significantly associated with the surgery of lateral lymph node dissection (LLND) (4). Though this article included the mrN stage, the complement of lateral lymph node assessment could make this study more clinically significant.
Furthermore, histological type, including adenocarcinoma, squamous cell carcinoma, undifferentiated carcinoma, etc., is a routine item in biopsy and postoperative pathology reports and affects prognosis and treatment options. It is also worth mentioning that perineural invasion is an essential prognostic factor. Though this article said it collected these pathological characteristics, it did not represent the results and explored them further in the following analysis. This study could have improved if it included the above factors.
Secondly, the receiver operating characteristic (ROC) curve analysis was used to evaluate the diagnostic efficacy of T2 and PD values in tumour differentiation and the mrN stage. However, several clinically relevant influencing factors exist, and univariate analysis cannot rule out potential confounding. Multivariate analysis, such as logistic regression, is recommended to improve the outcomes’ credibility.
Thirdly, this study used the mrN stage as the outcome when exploring the diagnostic performance of SyMRI, which was not so appropriate as they were both MRI features. If the mrN stage can be obtained directly from imaging, it is not so necessary to calculate parameters derived from SyMRI to predict the mrN stage.
Moreover, studies have shown that 20% to 34% of patients with colorectal cancer (CRC) present with synchronous liver metastases (5). Different locations and metastases of primary rectal cancer lesions directly affect treatment goals, surgical approaches, and patient prognosis (5-7). However, essential clinical characteristics in this study, including distant metastatic status and location of rectal cancer, were not included, which will affect the applicability of the conclusions.
Lastly, neoadjuvant therapy is one of the effective treatments for patients with cancer (8), especially among patients with low-risk, intermediate-advanced rectal cancer (9). However, only a portion of the patients is effective (10). The prediction of efficacy is a current clinical difficulty that needs to be solved urgently. In this article, 79.3% (69/87) of the patients received neoadjuvant therapy, but the predictive value of T2 and PD values in the efficacy of neoadjuvant treatment was not explored. If this study carries out further related research, It would be more clinically meaningful.
In summary, we appreciate the authors for their important and promising study. It highlights the noninvasively diagnostic value of SyMRI in patients with rectal cancer and the necessity of higher quality research in the future.
Supplementary file: Reply: ‘Synthetic magnetic resonance imaging predicts the prognostic evaluation of rectal cancer’.
Provenance and Peer Review: This article was a standard submission to the journal. The article did not undergo external peer review.
Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-22-624/coif). The authors have no conflicts of interest to declare.
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