P-340 Bidirectional chemotherapy for patients with gastrointestinal peritoneal carcinomatosis

Peritoneal carcinomatosis (PC) is a common manifestation in gastro-intestinal (GI) cancers with highest incidence in gastric and colon cancer. Around 20 % of patients developp isolated, unresectable PC with poor prognosis and low sensitivity to systemic chemotherapy. In most of the cases, disease progression results in bowel obstruction and malnutrition, making difficult the pursuit of systemic therapy. We aimed to describe a prospective cohort of patients with colon and gastric cancer with predominant peritoneal disease treated with bidirectional (intraperitoneal and systemic) chemotherapy in our institution. The primary objective was the feasibility of intraperitoneal administration, control of the peritoneal disease, defined as the absence of clinical and/or scannographic disease progression, and overall survival. Between 2017-2022 a total of 29 pts with PC received bidirectional (BD) chemotherapy. The main characteristics were as follow: 15 males (52%), median age of 55 years (IQR: 32-74); patients with primary colorectal (n=14, 48%) and gastric (n= 14, 48%) cancers.The majority had a mucinous histology (n=25, 86%). BD approach was decided by the multidisciplinary tumor board and 91% (n=27) had a baseline celioscopic exploration for peritoneal carcinomatosis index (PCI) assessment and peritoneal catheter (KT) placement. In 2 pts (7%) the peritoneal KT was placed by interventional radiology. The median index of baseline PCI was 20 (IQR: 8-34). BD chemotherapy (IP)was performed as first line(n=14,48%), second line :28%(n=8); further lines(n=6,21%) or in the adjuvant setting(n=1,3%). 59% (n=17) received IP oxaliplatin while 41%(n=12) received IP paclitaxel. All patients received concomitant intravenous chemotherapy: mainly 5FU -irinotecan (n=10,35%) or oxaliplatin(n=7,24%) based chemotherapy . The median number of BD cycles was 4 (IQR: 1-20); 2 patients (7%) received only one cycle of BD, because of bowel obstruction. The majority of patients (69%, n=20) had a morphologic stable (assessed by CT scan)disease as best response but a significant clinical benefit(less abdominal pain or ascites).Intermediate peritoneal exploration was done in 11 pts(38%). Five (n=17%) patients could access to a curative-intent surgery, two (7%) are still alive; one (3%) is disease free after a follow-up of 3 months The overall median duration of peritoneal disease control was 5.5 months (IC 95% 5.24 - 11.29) for all the group . The patients with gastric cancer had better numeric median duration of peritoneal disease control 8.64 months (95%CI 4.26-13.01) compared to patients with colon cancer 5.47months (95% CI: 2.65- 8.29) ,p-0.18. The median OS was 18.5 months(95%CI 18.00-26.85).The median OS for gastric cancer was numerically higher compared to colon cancer, without statistical difference (23 vs 22 months, p =0.5).62%(n=19) of patients received at least one line of treatment after IP administration. Tolerability: 41% (n=12) presented abdominal pain after Oxaliplatin IP administration; only 25% (n=3) had grade 2, during 24 h after IP administration.2 (n=7%) patients had peritoneal KT infection. Bidirectional chemotherapy seems feasible in patients with GI cancers and predominant peritoneal disease achieving interesting results in terms of disease control.Gastric patients seem to have longer control of the disease with BD chemotherpy probably because this approach was decided earlier compared to colorectal patients.