Background The incidence of gastric poorly cohesive carcinoma (PCC) is increasing. The prognosis for patients with peritoneal metastases remains poor and the role of cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) is controversial. The aim was to clarify the impact of gastric PCC with peritoneal metastases treated by CRS with or without HIPEC. Methods All patients with peritoneal metastases from gastric cancer treated with CRS with or without HIPEC, in 19 French centres, between 1989 and 2014, were identified from institutional databases. Clinicopathological characteristics and outcomes were compared between PCC and non-PCC subtypes, and the possible benefit of HIPEC was assessed. Results In total, 277 patients were included (188 PCC, 89 non-PCC). HIPEC was performed in 180 of 277 patients (65 per cent), including 124 of 188 with PCC (66 per cent). Median overall survival (OS) was 14.7 (95 per cent c.i. 12.7 to 17.3) months in the PCC group versus 21.2 (14.7 to 36.4) months in the non-PCC group (P < 0.001). In multivariable analyses, PCC (hazard ratio (HR) 1.51, 95 per cent c.i. 1.01 to 2.25; P = 0.044) was associated with poorer OS, as were pN3, Peritoneal Cancer Index (PCI), and resection with a completeness of cytoreduction score of 1, whereas HIPEC was associated with improved OS (HR 0.52; P < 0.001). The benefit of CRS-HIPEC over CRS alone was consistent, irrespective of histology, with a median OS of 16.7 versus 11.3 months (HR 0.60, 0.39 to 0.92; P = 0.018) in the PCC group, and 34.5 versus 14.3 months (HR 0.43, 0.25 to 0.75; P = 0.003) in the non-PCC group. Non-PCC and HIPEC were independently associated with improved recurrence-free survival and fewer peritoneal recurrences. In patients who underwent HIPEC, PCI values of below 7 and less than 13 were predictive of OS in PCC and non-PCC populations respectively. Conclusion In selected patients, CRS-HIPEC offers acceptable outcomes among those with gastric PCC and long survival for patients without PCC.

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e16538 Background: Pressurized intraperitoneal aerosol chemotherapy (PIPAC) is emerging as a new intraperitoneal laparoscopic delivery of chemotherapy to treat peritoneal metastasis (PM). First results from several malignancies appear promising in small series of patients. Prognosis of PM from gastric cancer (GC) is poor. Median survival is ranging from 3 to 13 months with systemic chemotherapy (SC) alone. Purpose: to evaluate the feasibility and potential benefits of PIPAC associated to SC in GC with PM in a palliative setting Methods: From a prospective database, we identified 91 consecutive patients considered with isolated unresectable PM from GC treated by an alternance of SC and PIPAC with low-dose cisplatin-doxorubicin (ratio 2/1) between January 2016 and January 2019 in our institution. End of follow-up was January 2020. Results: Median age was 56 years, 86% of patients had a signet ring cell adenocarcinoma with 86.7% of synchronous PMs.Median Peritoneal Cancer Index was 16 (3-39). A total of 346 PIPAC were performed with a median of 3 per patient (1-18). Median number of SC lines was 3 (2-3) resulting in a median number of SC cycles of 14 (11-20). After a median follow-up of X months, 21 patients were still alive. In the whole population, median OS from diagnosis was 15.1 months. PIPAC was introduced in association to first-line SC as maintenance or intensification therapy in 75 patients with a median survival from diagnosis of 14.7 months and a median PFS from PIPAC introduction of 6.3 months. For 16 patients, PIPAC was introduced due to progression after a first or second line of SC leading to a median OS of 20 months after diagnosis and 5.9 months after PIPAC introduction. Reasons to stop PIPAC were cancer progression, intraperitoneal access difficulties or PIPAC related morbidity, a cytoreductive surgery attempt in 61.7%, 19.8% and 18.5% respectively. A cytoreduction and HIPEC attempt was performed for 12 patients before 3 PIPAC and 3 after 3 PIPAC or more, leading to a median OS of 19 months for those patients. Twelve (13,2%) patients developed extra-peritoneal metastases during PIPAC. Conclusions: PIPAC appears safe and feasible showing promising results in control of PMs from gastric origin. Further randomized studies are required to document its benefits compared to SC alone.

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331 Background: PIPAC is a recent approach for intraperitoneal chemotherapy with promising results for patients with peritoneal metastasis (PM). It is a safe and well-tolerated treatment. Our aim was to report oncological outcomes after PIPAC for gastric PM. Methods: International retrospective cohort study of consecutive patients with gastric PM. Outcome measures were overall survival (OS), radiological response (RECIST), histological response by use of Peritoneal regression grading system (PRGS) and cytology, peritoneal cancer index (PCI) and symptoms. Results: 586 non-selected patients with a median age of 56 (47-64) years, 54% of them were female and underwent a total of 1566 PIPAC procedures. 37% of patients were treated with 2 or more lines of IV chemotherapy, median PCI at first PIPAC was 14 (7-24) and 63% of them were with signet ring adenocarcinoma. Grade III-IV morbidity was 5.1 % and 1.9% died within 30 days from PIPAC procedure. Median OS was 15.4 months from diagnosis and 20.1 months for patient with more than 3 PIPAC. 263/586 patients (44.9%) had ≥3 procedures ( pp: per protocol) with the following outcomes: RECIST: 4.3% complete response 11% partial remission, 44% stable; PRGS1 39% at PIPAC3 and negative cytology at PIPAC3 in 16% of patient. In multivariate analysis, 3 PIPAC or more HR 0.3 (95% CI 0.27-0.51), 2nd and 3rd line of chemotherapy HR 0.48 (95% CI 0.25-0.92) and CRS&HIPEC after PIPAC HR 0.3 (95% CI 0.18-0.51) were predictors for survival. Conclusions: Based on this large multicentre cohort study, PIPAC could be considered as an option for the treatment of PM from gastric cancer. More prospective study will validate this indication in the near future.