Definitely, effective and precise prognostic prediction in patients with malignancy is important for clinical decision-making and scientific research. Previous studies had reported that factors such as age, sex, CEA, tumor size, T and N stage, metastatic sites, and treatment were significant predictors related to survival outcome of mCRC patients [10]. Intuitive and convenient prognostic tools are what clinicians need. However, the inclusion of more information and a more individualized prognosis model will certainly predict the prognosis of patients more accurately.
Using the SEER database which covers about 28% of the population in the United States, we were able to collect sufficient samples and therefore developed and validated nomograms that predicting 1- and 3-year OS and CSS of patients with CRC and OLM. In the current study, we identified age, marital status, tumor location, T and N stage, serum CEA level, tumor deposit, histological grade, primary tumor surgery, chemotherapy, radiotherapy, and income were significantly associated with OS. As for CSS, metastatic tumor surgery was a significant prognostic factor, but not income. The nomograms were created based on these significant prognostic factors. As for high-risk OLM patients, more aggressive treatments are recommended, and the follow-up interval is encouraged to be shortened appropriately to detect the occurrence of an endpoint event in the early stage.
Unsurprisingly, our results suggested that chemotherapy and surgical treatment were the main prognostic factors in CRC patients with OLM, and the primary site was also significantly associated with the prognosis. Indeed, it has been widely recognized that chemotherapy can improve the prognosis of mCRC patients, left-sided tumor location is also a predictor for better prognosis [11]. Moreover, surgery is still the superior option for CRC patients who are able to undergo surgery, even for patients with mCRC. A comprehensive review including 26 clinical studies reported that the survival outcome of CRC patients with limited metastatic diseases were significantly improved by R0 resection of metastases [12]. Likewise, several retrospective studies and meta-analyses had demonstrated an association between primary tumor resection and improved OS in CRC patients with metastatic disease [13–16]. However, the data have not been entirely consistent across the published studies [17–19]. Of note, the correlation between radiotherapy and prognosis should be based on rectal cancer, and for the sake of simplicity, no distinction was made between left colon cancer and rectal cancer in the present study. Consistent with previous findings, our results suggested that sex, race, and tumor size had no effect on long-term survival for patients with LM from CRC [20]. Unlike it was clear that age was a prognostic factor in mCRC patients [21], whether sex, race, and tumor size had effects on the prognoses of patients with mCRC is still controversial. Some studies reported that white descent, male sex, larger primary tumor size predicts poorer survival [10, 22, 23].
In addition to prognostic nomograms, the present study identified several risk factors associated with LM from CRC. Combined with nomogram for prediction of the risk of LM from CRC [10, 20], clinicians and researchers can effectively identify patients at high risk of LM and monitor follow-up computed tomography closely. Moreover, we confirmed that different metastatic sites would affect the prognosis of CRC patients. Further exploration for why CRC patients with OLM had a better prognosis is worth looking forward to.
There were some limitations in our study. First, the nomograms were developed on the basis of retrospective data, prospective validation is needed. Second, some important information such as chemotherapy regimens, targeted therapy, molecular pathology, and genetic test were not recorded in the database. Third, the data of the timeline of other information such as CEA levels in patients were not available too. Finally, because of the limitations of our data, we didn’t explore the effect of the factors, such as histological type and the number of positive lymph nodes, on the prognosis of mCRC patients. Further prospective studies with more critical information are warranted for model improvement and independent validation.