GC has two of the highest morbidity and fatality rates among cancers, originating from the gastric mucosal epithelium . It can grow in various sites of the stomach and can easily develop hematogenous or lymphatic metastases . In recent years, GC started to occur in young patients . It is known that, even at early stages, GC may recur or develop metastases; therefore, it is important to maintain routine treatment and reviews to prolong patient survival . Every coin has two sides; excessive treatment and examination will increase the financial burden on patients; however, it will affect GC prognosis. For example, enhanced computed tomography, which is effective in diagnosing GC, is not only expensive but also extremely unhealthy. Therefore, it is important to build a reliable nomogram that can accurately evaluate the recurrence risk of patients with GC postoperatively. Many studies revealed few GC prognostic factors, such as tumor size and invasion depth. However, these factors were limited and focused only on tumor growth and not on the patients’ general condition and treatment information. Our research was based on the SEER database and included different races, innovatively adding some indicators that were proven to be associated with many kinds of cancer  ; such indicators, such as marital status, are rarely used for GC. Although some studies have used nomograms to predict the prognosis of patients with GC   , we attempted to establish a prognostic nomogram combining multifarious clinical indicators, pathological characteristics, and treatment information to evaluate the probability of 3- and 5-year OSs of such patients.
In our study, the nomogram was more credible and persuasive as the outcomes were obtained from the data of the training set and then validated by testing set. First, we performed a univariate analysis including all factors; of these factors, we selected those that were significant, including age, sex, histology, and surgery, and brought them into the multivariate analysis. The multivariate analysis revealed that age at diagnosis, sex, histology, stage_T, surgery, tumor size, and marital status were independent prognostic factors of OS. A nomogram was constructed based on these factors, and the C-index was 0.791. Calibration curves showed great consistency between prediction and observation results, and there was a significant difference between the high-risk and low-risk groups. Moreover, the AUCs of 3- and 5-year survivals were 0.774 and 0.773, respectively.
The nomogram has been continuously proven to be a reliable and accurate prognostic prediction tool in recent studies. It can evaluate survival using various comprehensive indicators and acquire a better prediction effect than other prediction tools.
For patients with early-stage GC, based on the nomogram obtained in this study, combined with clinical information, we can obtain a postoperative patient risk rating.
For high-risk patients, review frequency and follow-up times should be increased.
Patients themselves should pay more attention to symptom fluctuation and improvements in lifestyle.
From the seven factors included in our nomogram, tumor size was the largest contributor to OS. This is in line with our usual perception, which is that a larger tumor is more aggressive and that a barely visible carcinoma in situ is indolent. Ohashi et al. thought that both tumor size and depth could be used as combined prognostic indicators . Our scoring system also included tumor invasion depth, and the T1b score was moderately higher than the T1a score. Tumors with a higher T stage have deeper infiltration, and there are more vascular and lymphatic vessels in the submucosa than in the mucosa, causing tumor cells to spread further and making them more difficult to remove; this directly worsens patient survival. Age was also an OS risk factor. Looking at the overall trend, old patients scored higher nomogram scores and had a worse prognosis than young patients.
This might be attributed to the fact that elderly patients have a worse general condition and immune tumor cell clearance and more underlying diseases than the former.
It is worthy to note that different surgical methods also have a certain impact on prognosis. Patients who did not undergo surgery had the worst prognosis, indicating that surgery is still the most effective treatment for GC. Patients who underwent partial gastrectomy scored best on the nomogram, while patients who underwent endoscopic surgery and total gastrectomy had similar scores. This does not mean that total gastrectomy is not effective for treating GC because the condition of patients who need total gastrectomy might be more serious. Whether partial gastrectomy or endoscopic surgery is better for early-stage small-diameter GC has remained a controversial issue in clinical practice, and a few studies have been dedicated to provide references to choose the correct treatment. Nishizawa et al. indicated that patients receiving ESD generally had a better quality of life postoperatively; however, they also had a higher incidence of metachronous GC . Mun et al. reported that endoscopic surgery has fewer complications than traditional surgery based on the fact that the OS of the former is no less than that of the latter . Nomura et al. suggested that we should try to reduce the extent of gastrectomy if GC can still be cured . Our nomogram showed that partial gastrectomy was generally better than endoscopic surgery, indicating that, according to the current medical level, we should be cautious in using endoscopic surgery instead of traditional surgery. For patients with large tumor diameters and poor histological types, partial gastrectomy should be preferred to ensure radical resection. Because of its lower trauma rate and higher safety, endoscopic surgery can be applied to patients who cannot tolerate surgery due to advanced age or underlying diseases.
Marital status, a factor that is rarely enrolled in GC research, also showed moderate influence on survival in our nomogram.
Married patients had the best prognosis, followed by single patients, and the prognosis of separated patients was the worst.
This result was consistent with the Kaplan-Meier survival curve. We speculate that this might be due to the fact that married patients had better financial conditions and emotional encouragement, while separated patients might be more likely to experience financial difficulties emotional loss. Moreover, our nomogram showed that gender and histology also had an important impact on prognosis. Male patients had higher scores and poorer prognoses. This might be related to genetic differences between men and women. Li et al. reported that the expression of different core genes and differences in pathways were associated with the variation observed among patients with GC of different races and sexes [25
]. Different lifestyles as a result of different sexes might also affect prognosis.
Considering histology, signet ring cell carcinoma had the worst survival according to the nomogram.
This result is also consistent with traditional clinical knowledge. Riihimäki et al. demonstrated that signet ring adenocarcinomas had a higher probability of metastasis within the peritoneum, bone, and ovaries than adenocarcinomas [26
]. The higher risk of metastasis may be the reason for the worse prognosis in patients with signet ring cell carcinoma.
To the best of our knowledge, this is the first SEER-based nomogram combining comprehensive clinical indicators to predict OS in patients with early-stage GC. However, our research has some limitations.
To improve the reliability of our study, we divided the screened SEER data into training and testing sets at a ratio of 3:1; however, the validation of the local medical center data was still missing.
Second, retaining unclearly classified data or data displayed as "unknown" not only enlarged the scope of application of the nomogram, but also increased mutual interference between data to a certain extent; this affected the accuracy of the nomogram. Third, some well-known risk factors of GC, such as family history, alcohol and Helicobacter pylori (HP) infection, were not enrolled. These indicators were scarce in the SEER database as it was difficult to acquire them. For example, there is no clear standard to determine whether the patient has a history of drinking alcohol based on the amount of alcohol consumed, the frequency of drinking, and the time of abstinence. Moreover, HP infection examinations are not routinely performed in many areas, making it difficult for the data to be applied in large databases.