In this study, the data from 3,829 patients in the SEER database were used to create a prognostic nomogram. Although several nomograms have been established previously for patients with LARC undergoing surgical resection after NCRT, the study by Zhifang et al. covering 785 cases (17), has certain limitations as it is a single-center study and their results lacked externally validation. The study by Valentini et al. was based on five European randomized clinical trials (18), but the variables they employed differed greatly from those in our analysis, which included tumor size, CEA level, tumor grade, marital status, and, in particular, LODDS. To the best of our knowledge, this is the first nomogram based on the SEER database that incorporates LODDS to predict the OS of patients with stage II/III rectal cancer undergoing surgical resection after NCRT.
Through multivariable Cox regression analysis, ten parameters, including race, sex, age, marital status, T stage, tumor grade, tumor size, LODDS, CEA level, and postoperative chemotherapy were determined as independent prognostic factors. It was obvious that LODDS greater than − 0.4 contributed most to the poor prognosis, followed by T4b stage.
As we all know, lymph node status plays a significant role in rectal cancer patients’ prognosis. In recent years, in addition to AJCC N stage, many scholars have proposed and analyzed other parameters to evaluate the status of lymph nodes, such as LODDS and the lymph node ratio (LNR). Although AJCC N stage is currently the most widely used method for lymph node classification, many researchers have pointed out its limitation since it only considers the number of positive lymph nodes and ignores the total number of lymph nodes (TLN) retrieved during surgery. In rectal cancer, TLN has been proven to be an independent prognosis-related factor (19–21). For accurate staging of colorectal cancer, removal of at least twelve lymph nodes was recommended by AJCC. LNR involves both TLN and PLN and has been claimed to be more accurate than AJCC N stage for rectal cancer (22, 23). However, other scholars have noticed that when TLN are either all non-metastatic or all metastatic, patients with the same LNR values might be extremely varied. LODDS, as a novel lymph node classification, can overcome the drawbacks of LNR and increase the accuracy for prognostic evaluation, and studies have shown its superiority to LNR in rectal cancer (16, 24, 25). For LARC, LODDS was confirmed to perform better than both AJCC N stage and LNR in terms of prognostic predictive value (13, 14, 26). Therefore, the nomogram wil be more convicing and effective if LODDS is incorporated into it.
In this study, 56.9% of patients who received postoperative chemotherapy, seemed to have a better outcome. On the other hand, several large randomized controlled trials concluded that postoperative chemotherapy could not improve the OS of rectal patients undergoing surgery after NCRT (27–29). These trials, however, had significant limitations, such as poor adherence in the European Organization for Research and Treatment of Cancer trial 22921. Therefore, it remains uncertain if these patients will benefit from postoperative chemotherapy. According to current National Comprehensive Cancer Network (NCCN) recommendations, rectal patients with tumors staged as T3 or N1 and higher should consider postoperative chemotherapy after neoadjuvant chemotherapy (30). However, experts convened by the European conference on rectal cancer concluded that there is currently insufficient evidence to demonstrate the benefits of receiving adjuvant chemotherapy after preoperative chemoradiotherapy; hence, postoperative chemotherapy cannot be recommended (31). In this way, more comprehensive and conclusive researches will be conducted in the future.
To summarize, the probability of 24-, 36-, and 60-month OS of patients with stage II/III rectal cancer undergoing surgical resection after NCRT can be simply calculated by summing the points on the nomogram for each patient's matching factors. The prognostic factors included in this nomogram can be quickly accessed in clinical work, making it as a practical tool. In additional, by employing risk group stratification, patients who are at high risk can be easily tracked down and treated with a more personalized approach in early intervention. Finally, the nomogram was validated and shown to be repeatable and reliable, with satisfactory discriminative power.
There are some limitations to this study. First, as this was a retrospective analysis based on the SEER database, there was bound to be some degree of selection bias. Second, the SEER database did not offer certain information that could have affected patient outcomes, such as surgical margins, lymph/vascular or perineural invasion, and chemotherapy/radiation regimen. Future predictive models could benefit from the use of molecular tumor markers as well as genetic data.