SOX/FOLFOX+nivolumab followed by conversion surgery for HER2 negative primary gastric or gastroesophageal junction cancer with oligo-metastasis or borderline resectable tumors: Early results of a consecutive 41 cases.

487 Background: Gastric or gastroesophageal junction cancer with oligo-metastasis or borderline resectable tumors could be cured by conversion surgery after primary chemotherapy. Because SOX/FOLFOX plus Nivolumab showed high clinical response regardless of CPS score, this nivolumab-based chemotherapy followed by surgery may be promising strategy for these tumors. Methods: The study examined the patients who had HER2 negative primary gastric or gastroesophageal junction cancer with synchronous oligo-metastasis or borderline resectable tumors. Oligo-metastasis was defined as peritoneal dissemination localized to the upper abdomen, para-aortic lymph node metastasis, liver metastasis limited up to 3 segments, mediastinal lymph node metastasis, ovarian metastasis, or esophageal intramural metastasis. Borderline resectable tumors were defined as regional lymph node metastasis forming bulky mass or primary tumors invading adjacent organs. The patients with these tumors were treated with primary chemotherapy with SOX/FOLFOX plus Nivolumab for 3 to 22 months, then were proceeded to conversion surgery in case the tumors are responded to chemotherapy and are considered to achieve R0 resection based on the MDT conference. Results: During November 2021 and February 2024, 41 consecutive patients were included in the study. Disease status was peritoneal dissemination in 1, para-aortic lymph node metastasis in 26, liver metastasis in 5, mediastinal lymph node metastasis in 1, ovarian metastasis in 1, esophageal intramural metastasis in 2, bulky nodal metastasis in 6, and primary tumors invading pancreas in 1 (distant oligo-metastasis in 34 patients and borderline resectable in 7). CPS score was >5 in 13, 5> and >1 in 23, and >1 in 5 patients. Chemotherapy regimen was SOX+Nivo in 38 and FOLFOX+Nivo in 3. Of 41 patients, 33 (80.5%) (SOX+Nivo: 30, FOLFOX+Nivo: 3) were proceeded to the conversion surgery, and 32 patients achieved R0 resection. 6 patients showed disease progression and 2 patients were judged as unresectable. Major pathological response (disappearance more than 80% of the primary tumor) rate was 54.5% (18/33) and pCR rate was 33.3% (11/33). Conclusions: SOX/FOLFOX plus Nivolumab for HER2 negative gastric or gastroesophageal junction cancer with oligo-metastasis or borderline resectable tumors achieved a high R0-conversion surgery rate and pathological response rate.