DFS, OS Rates Similar After Gastric Cancer Treatment With SOX, SOX Plus Radiotherapy

The SOX chemotherapy regimen for gastric cancer consists of S-1, an oral fluoropyrimidine, in combination with oxaliplatin. While adjuvant chemotherapy and chemoradiotherapy are common gastric cancer treatments, debate persists on whether radiotherapy should be administered after D2 radical resection. 

A phase III trial has compared the efficacy of SOX alone (SOX) with SOX plus radiotherapy (SOXRT) for the adjuvant treatment of patients with gastric cancer and stage T4 or positive lymph nodes after D2 resection. 

A total of 620 patients were randomly assigned 1:1 to undergo SOX or SOXRT. Patients in the SOX arm received six cycles of chemotherapy, consisting of S-1 30-40mg/m2 on days 1-14, and oxaliplatin 130mg/m2 on day one, every three weeks. 

The SOXRT arm administered one cycle of induction chemotherapy with SOX 21 days before beginning radiotherapy. The radiotherapy consisted of a total dose of 50.4Gy in 28 fractions; 1.8Gy per day and five fractions per week were administered simultaneously with concurrent S-1 chemotherapy at a dose of 50 mg. After the completion of radiotherapy, three cycles of SOX were administered to patients 3–4 weeks later at the same dose as the induction chemotherapy. 

The primary endpoint of the study was disease-free survival (DFS). The median DFS follow-up period was 64 months, and 263 DFS events occurred. The 3-year DFS rates for the SOXRT and SOX arms were 71.7% and 71.4%, and the 5-year DFS rates were 60.2% and 59.2%, respectively. 

The median overall survival (OS) follow-up period was 69 months, and 188 OS events were observed. The 3-year OS rates for the SOXRT and SOX arms were 81.1% and 79.8%, while the 5-tear OS rates were 74.9% and 73.2%, respectively. 

A statistically significant difference was not observed between the two treatment arms in terms of DFS (HR 0.930; P=0.56) and OS (HR 1.003; P=0.99), and adverse events were expected with manageable toxicity. 

For patients with T4 lymph node-positive gastric cancer with D2 resection, the addition of radiation therapy to a postoperative adjuvant SOX regimen did not significantly improve DFS or OS rates.