The MAGIC trial, ACTS-GC study, and CLASSIC trial have provided high-level evidence of the benefit of adjuvant chemotherapy in GC [5, 6, 7]. However, there is no global agreement on chemotherapy regimens and durations for GC. Although 6 months of XELOX, SOX, FOLFOX treatment or eight 6-week cycles of S-1 are recommended for patients with advanced GC after D2 gastrectomy in China [8], many patients cannot complete the full course of treatment because of adverse events. In the ACTS-GC study, only 340 (65.8%) of the 517 patients receiving S-1 continued treatment for 12 months, including 158 (46.5%) dose reductions [15]. In the CLASSIC trial, only 346 patients (67%) competed eight cycles as planned. Meanwhile, 48% of patients required capecitabine dose reductions, and 47% required oxaliplatin dose reductions. Ninety percent of patients required dose modification because of adverse events, and the most common adverse events in the chemotherapy group were nausea, vomiting, neutropenia, decreased appetite, diarrhea, and peripheral neuropathy. Peripheral neuropathy, a cumulative dose-limiting toxicity associated with oxaliplatin, occurred in 56% of patients who received chemotherapy [7]. Neurotoxicity usually peaks within a few months after the last dose of oxaliplatin, making it difficult to personalize treatment with an empirical dose. Such toxic effects can last long after treatment and severely affect patients’ daily living activities such as writing, dressing and handling objects [16]. Given the cumulative nature of oxaliplatin-induced neurotoxicity, patients may benefit from a shorter duration of adjuvant treatment without sacrificing efficacy. In our study, for patients with stage II–III GC after D2 gastrectomy, the 5-year OS rates for groups A, B, C and D were 52.3, 73.7, 72.0, and 53.3%, respectively. The results suggest that shortening the duration of adjuvant chemotherapy with fluorouracil and oxaliplatin to 4–6 cycles administered every 3 weeks or 6–9 cycles administered every 2 weeks (group C) produced similar efficacy as 7–8 cycles administered every 3 weeks or 10–12 cycles administered every 2 weeks (group B). No treatment (group A) or early termination of postoperative treatment (group D) was related to worse OS. Subgroup analysis found no statistical difference between groups B and C concerning OS. Multivariate analysis revealed that the number of adjuvant chemotherapy cycles was an independent prognostic factor.
The addition of eight cycles of oral capecitabine to the eight-cycle XELOX regimen did not significantly improve 3-year OS in patients with stage II–III gastric cancer [9]. Similarly, prolonged postoperative chemotherapy for less than 1 year, less than 2 years, or more than 2 years did not significantly improve survival [12]. However, more patients in the prolonged group experienced more adverse events [9, 12]. Three months of treatment with CAPOX has been introduced for patients with stage III colon cancer in the lower-risk group based on the IDEA collaboration, a large-scale, prospective, pooled analysis of phase 3 trials. As expected, a shorter duration of treatment significantly reduced the incidence and severity of adverse events without sacrificing efficacy [14]. Furthermore, 6 months of treatment with S-1 proved more effective than gemcitabine in treating resected pancreatic cancer based on the JASPAC 01 study, an open-label, multicenter, randomized phase 3 trial [17]. Qu et al. [13] conducted a retrospective analysis of 237 patients with stage IB–IIIC GC who received four, six, or eight cycles of FU plus oxaliplatin, FU plus non-oxaliplatin combinations, or FU monotherapy after D1 or D2 radical gastrectomy. The 5-year OS rates for eight, six, and four cycles were 65.8, 74.0, and 41.2%, respectively, which illustrates that six cycles of FU-based adjuvant chemotherapy are adequate. We retrospectively analyzed 428 patients with stage II–III GC after D2 gastrectomy, and the 5-year OS rates for groups B and C were 73.7 and 72.0%, respectively, which were higher than those of patients who completed eight cycles and comparable to those of patients who completed six cycles in the study by Qu et al.. Our results were also comparable with those of the ACTS-GC study, in which all patients with confirmed stage II–III gastric cancer underwent D2 gastrectomy, and the 5-year OS rate was 71.7% in the S-1 group [6]. To reduce toxicity while maintaining efficacy, patients should avoid the two additional cycles of FU plus oxaliplatin without worrying about adverse outcomes. Regarding S-1 monotherapy, JCOG1104 [OPAS-1], an open-label, phase 3, non-inferiority, randomized trial, found that four courses of S-1 (treatment lasted for 6 months) was inferior to eight courses of S-1 (treatment lasted for 1 year) concerning relapse-free survival (RFS) among patients with confirmed stage II GC [11]. Hence, eight courses of S-1 remain the standard treatment for stage II GC.
It is important to note that all patients in our study underwent D2 gastrectomy, and thus, the optimal treatment after D0 or D1 gastrectomy may be different. The INT-0116 study, in which 36% of patients underwent D1 lymph node dissection and 54% underwent D0 lymph node dissection, found that postoperative chemoradiotherapy significantly improved RFS and OS in patients with GC. The updated analysis with a median of more than 10 years of follow-up revealed a strong persistent benefit [4, 18]. However, the intergroup CALGB 80101 trial demonstrated that more intensive systemic chemotherapy combined with postoperative chemoradiotherapy (as shown in INT-0116) produced no survival benefit [19]. Moreover, the ARTIST trial failed to demonstrate that the addition of radiotherapy to postoperative adjuvant chemotherapy significantly improved DFS in patients who underwent D2 gastrectomy [20]. Therefore, it appears that postoperative chemoradiotherapy can compensate for inadequate surgery.
No survival difference found between traditional open and laparoscopic-assisted approaches in our study. Regarding short-term outcomes, laparoscopic-assisted D2 gastrectomy proved feasible compared with traditional open surgery in some randomized controlled trials, but the long-term efficacy has not been clarified [21, 22]. Our study found that patients older than 60 years were less likely to survive than those younger than 60 years, suggesting that age affects the survival of GC [23, 24]. To our surprise, blood loss exceeding 100 mL during surgery was a risk factor for both overall mortality and recurrence in univariate and multivariate analyses. This finding is consistent with many research results that operative blood loss predicts worse survival in patients undergoing surgery [25–27], which has also been reported for a variety of other malignancies, such as pancreatic [28, 29], colorectal [30–32], and lung cancers [33]. BMI, tumor size, year of surgery, and excision extension were associated with increased blood loss [25, 26, 30]. Our research did not analyze data concerning the time between surgery and adjuvant chemotherapy, which did not exceed 3 months in our inclusion criteria. From previous studies, the duration of adjuvant chemotherapy, but not the period between surgery and chemotherapy, affected OS in GC [34, 35].
Some limitations of this study should be considered. First, as a retrospective study, our ability to obtain detailed data regarding short- and long-term chemotherapy-related adverse events was limited, especially concerning peripheral neuropathy. In the CLASSIC trial, the incidence of all adverse events was as high as 99% among 496 patients in the chemotherapy group. Although different grade 3 or 4 adverse events were infrequent, ranging in incidence from less than 1 to 22%, the cumulative incidence was also as high as 56% in 496 patients [7]. Because some adverse events are associated with survival [36, 37], further studies are needed to confirm the impact of those adverse events on intergroup survival differences. Second, patients in our research received one of three different chemotherapy regimens (SOX, XELOX, and FOLFOX). However, there is a lack of prospective studies to determine which regimen is superior. Current studies suggest that XELOX regimen does not result in a greater survival benefit compared with FOLFOX6 regimen [38], and the SOX therapy has similar survival benefits to XELOX in Chinese patients with GC following D2 gastrectomy[39]. Additionally, because groups B, C, and D were balanced concerning the receipt of these three regimens, it is likely that differences in the chemotherapy regimen do not explain the differences in survival among the groups. Third, because of the relatively high recurrence rate in patients with gastric cancer, it is unlikely that an ethical recommendation would be made to assess the optimal duration of adjuvant therapy in a prospective manner. We did the first retrospective analysis ever. Although all patients in the study were collected consecutively based on inclusion and exclusion criteria, there was indeed a lack of fair matching of clinical parameters (Age, BMI, Postoperative complications and Tumor length/diameter) between groups, mainly between group A and the other three groups. For patients in group A, 44 patients refused chemotherapy due to personal willingness, 21 patients did not receive chemotherapy due to advanced age (65 years or older), and 10 patients due to self-conscious physical weakness, and 11 patients refused chemotherapy after recovery from complications (gastroparesis or anastomotic fistula). However, all these patients recovered ECOG score of 0–1 within 3 months after the operation. This cohort study suggested that age ≥ 60 years was an independent risk factor for OS, which may have significant intergroup influence on prognosis, while BMI, tumor length/diameter and postoperative complication were not independent prognostic factors. The median age of group A, group B, group C and group D was 66 years, 57 years, 60 years and 62 years, respectively. When the median age of both groups B and C was ≤ 60 years and the median age of group C was higher than that of group B, the survival of patients in group C was not worse than that of group B, which also confirmed the feasibility of chemotherapy duration in group C from another aspect. As for groups A and D, both median age was ˃60 years and the median age of group D was lower than that of group A, but the survival of patients in group D was not better than that of group A.