Lymph node metastasis has a significant influence on the prognosis of patients with GC, and various methods are used to identify and determine the number of metastatic lymph nodes, including ultrasonography, endoscopic ultrasound sonography, CT, magnetic resonance imaging, and positron emission tomography (PET). Among these, MDCT is accepted as the most powerful diagnostic method. Preoperative diagnosis is made mainly by node size rather than shape or the enhanced contrast pattern. Node size is easy to obtain and is a reproducible criterion. It can also be obtained by simple CT without contrast enhancement in patients with renal dysfunction or atopy. The cutoff values used in this study, a minor axis of ≥ 8 mm or a major axis of ≥ 10 mm, are commonly used for the diagnosis of metastasis. The sensitivity was 44.4%, and the positive predictive value was 80.0%; these are consistent with the results of previous reports [
5‐
7]. Although sensitivity may differ depending on the location of the tumor and the nodes, we did not consider it in this study. Fukagawa et al. investigated the diagnostic accuracy of lymph node metastasis by CT in a clinical trial, with the same size criteria as that used in this study, and found that the sensitivity and positive predictive values were 62.5% and 77.7%, respectively [
8]. In clinical practice, PET can be used to diagnose lymph node metastasis, especially metastasis of distant nodes. However, lymph nodes near the primary tumor are sometimes difficult to diagnose accurately, and the histological type can influence their detection. The sensitivity of PET scans may be decreased in histologically diffused GC tumors because of low glucose transporter 1 (GLUT1) expression that reduces fluorodeoxyglucose uptake. Therefore, the usefulness of the routine preoperative PET evaluation for the diagnosis of lymph node metastasis is limited [
9]. Also, PET may help us diagnose the lymph node metastases accurately, but in this study, not all of the patients have diagnosed with these modalities; thus, we have considered only with CT.
There were quite few reports about the relationship between histological types and lymph node involvement in GC. In this study, we considered that preoperative histological types would help us make a decision on how to treat patients with severe GC. Recently, preoperative chemotherapy has been attempted to further improve the prognosis of patients with advanced GC. Several clinical trials have been conducted to evaluate the efficacy of NAC in patients with GC, and in Japanese gastric cancer treatment guidelines 2018 (ver. 5), NAC is recommended for patients with extensive, bulky lymph node metastasis [
1,
10‐
12]. However, cT1/T2 tumors may be mostly cured safely by initial surgery without preoperative chemotherapy, and prolonged NAC is occasionally accompanied by disease progression [
8]. Teranaka et al. recently reported that tub2 and pap show higher incidence of lymph node metastasis than tub1, so individualization of tub1, tub2, and pap is important when they consider endoscopic treatment [
13]. There was no literature that has been shown about the relationship between histological types and lymph node involvement, but in this study, the size of metastatic lymph node of differentiated adenocarcinoma might tend to be larger than that of undifferentiated adenocarcinoma because there were a lot of overdiagnosis cases. This speculation needs to be clarified in further studies. We evaluated diagnostic accuracy by histological type and found that only patients with advanced undifferentiated GC and cN2 ≤ or bulky metastases are likely to benefit from aggressive treatment with NAC. Precaution would avoid a false indication of the potential benefit of NAC in patients who would have a favorable prognosis following standard treatment, surgery, and postoperative chemotherapy. Thus, we considered that if the accuracy of the diagnosis of lymph node metastases would be improved, NAC may be effective. Further studies with large patient cohorts should be conducted to confirm these results.