Clinical Significance Of Peritoneal Molecular Markers In Patients With Locally Advanced Gastric Cancer (Lagc) Without Macroscopic Peritoneal Implants Treated With Perioperative Chemotherapy (Cht).

e15583 Background: Presence of malignant cells in the peritoneal lavage (Cyt+) of patients with LAGC in absence of macroscopic peritoneal implants reflects bad prognosis and is a surrogate of metastatic disease. The presence of molecular markers (Mol+), such as CEA and CK20 mRNA, had also been suggested to carry the same bad prognosis as Cyt+ after upfront curative gastrectomy. There is no recommendation about the management of Mol+ patients (pts) within the current perioperative ChT. Methods: We retrospectively analyzed all pts treated in our high volume multidisciplinary team between 2011 – 2015, with LAGC amenable to surgical resection, without macroscopic peritoneal implants in laparoscopy staging and treated with perioperative ChT. Pre-treatment peritoneal Cyt and Mol analysis (CEA and CK20 mRNA detected by RT-PCR), as well other clinical factors were analyzed. Results: From a total a 310 pts, 60 were included. Median follow up was 72.9 months (m). Mean age was 60y, 37% had PS0, 37% had diffuse histology, 85% wereT4(a-b), 93% N+ stage and 50% were located in gastric body. Accordig Cyt and Mol markers: 3% were Cyt+ and 18% were Mol+, 63% were Cyt-/Mol-, 15% Cyt-/Mol+, 3% Cyt+/Mol+, 0% Cyt+/Mol-, and 18% were Cyt or Mol unknown (uk). 83% underwent gastric surgery, of them, 93% achieved R0. Median PFS (mPFS) was 61.9m. mPFS for Mol+ was 11.0m (95%CI 2.6-19.4) vs the rest (Mol-/uk and Cyt +/-/uk) 69.9m (95%CI 45.0-94.8), p < 0.001. HR = 3.8. mOS was 68.3m. mOS for Mol+ vs the rest was 20.7m (95%CI 4.5-36.8) and not reached, respectively, p = 0.002. HR = 3.4. Mol+ pts who underwent surgery had longer mOS than Mol+ pts which did not (not-reached vs 7.8m (95CI% 3.4-12.9), p = 0.03). In the multivariate adjusted analysis PS (0 vs 1-2) and Mol (- vs +) were significant both for mPFS and mOS. Mol+: HR = 4.0 (95%CI 2.0-11.0),p < 0.001 for mPFS and HR = 5.4 (95%CI 1.9-14.9),p = 0.001 for mOS. Conclusions: Molecular peritoneal analysis may identify a subset of LAGC patients with bad prognosis despite negative cytology and absence of peritoneal macroscopic implants (Cyt-Mol+). Gastric surgery and perioperative chemotherapy may improve prognosis in some Mol+ patients