Peritoneal mesothelial cells (PMC) cover organ surfaces in the abdominal cavity. In this study, lineage tracing revealed that the PMCs guide cancer cell invasion in the gastric wall and in peritoneal metastatic lesions. Serosal PMCs covering the stomach surface entered the gastric wall to create a novel niche that favored gastric cancer cell invasion. PMC infiltration was induced by incorporation of cancer cell-derived, Wnt3a-containing extracellular vesicles. Infiltrated PMCs in turn promoted subserosal invasion of cancer cells. Mutual attraction between cancer cells and PMCs accelerated tumor invasion in the gastric wall, and PMC-led cancer cell invasion in disseminated tumors within the abdominal wall and diaphragm. Addition of the carboxyl terminus of Dickkopf-1 attenuated directional invasion of PMCs toward cancer cells both in vitro and in the gastric wall in vivo PMCs were sensitive to the aldehyde dehydrogenase (ALDH) inhibitor disulfiram (DSF), as ALDH activity is elevated in PMCs. Wnt3a upregulated ALDH, and addition of DSF inhibited the invasive properties of PMCs, whereas DSF pretreatment suppressed gastric infiltration of PMCs and subserosal invasion by cancer cells. Our results suggest that stabilization of PMCs may become an effective therapy for the prevention of local invasion and metastasis of gastric cancer. Cancer Res; 77(3); 684-95. ©2016 AACR.

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9589 Background: KRAS mutations are one of the common oncogene drivers in non-small cell lung cancer (NSCLC), and the development of several targeted drugs for KRAS-mutated NSCLC is now ongoing. However, the clinical impact of KRAS mutation subtypes or concomitant other gene mutations in NSCLC patients (pts) remains unclear. Methods: In a nationwide genomic screening project (LC-SCRUM-Japan), we have prospectively analyzed lung cancer pts for genetic alterations and tumor mutation burden (TMB) by next-generation sequencing system, and for PD-L1 expression by immunohistochemistry (22C3 antibody). The therapeutic efficacy and survival of KRAS-mutated non-squamous (non-sq) NSCLC pts were evaluated using a clinico-genomic database of the LC-SCRUM-Japan. Results: A total of 5166 non-sq NSCLC pts enrolled from 2015 to 2019. KRAS mutations were detected in 794 pts (15%; G12C/G12D/G12V/G12A/G13X/others = 232/186/165/66/61/84). Among the 794 pts, TMB and PD-L1 expression were analyzed in 128 and 79, respectively, and 218 received PD-1/PD-L1 inhibitors (IO) after 1st-line chemotherapy. The median age was 66 years (range, 29-89). 142 pts (65%) were male and 172 (78%) were smokers. Concomitant STK11 mutations were detected in 33 pts (15%) with no difference in the mutation frequency among KRAS mutation subtypes. KRAS G12C was significantly associated with high TMB (≥ 10 mut/Mb) (p = 0.03), and KRAS G12C or G12V with high PD-L1 expression (≥ 50%) (p = 0.02). In pts who received IO, median progression-free survival (mPFS) was significantly longer in pts with KRAS G12C or G12V than in those with other KRAS mutations (4.7 vs 2.0 months, hazard ratio (HR) 0.58 [95%CI 0.43-0.78], p < 0.01). Among pts with KRAS G12C or G12V, mPFS of IO was significantly shorter in pts with concomitant STK11 mutations than in those without (1.8 vs. 5.7 months, HR 1.97 [95%CI 1.06-3.41], p = 0.02). These correlations were not observed in platinum-containing chemotherapy (Plt-CTx). There were also no significant differences in IO and Plt-CTx efficacies between with and without other concomitant mutations, such as TP53, RB1, CDKN2A and PTEN mutations. Conclusions: Non-sq NSCLC pts with KRAS G12C/V were more sensitive to IO therapies than those with other KRAS mutations, but KRAS G12C/V-positive pts with concomitant STK11 mutations were less sensitive than those without. These results could be highly informative in the development of novel targeted therapies for KRAS-mutated NSCLC.

Background: Endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) is generally performed for the diagnosis of hilar/mediastinal lymph node metastasis in patients with lung cancer. Recently, a 25-gauge (G) needle became available, but robust evidence of its usefulness in routine clinical practice is still lacking.Methods: A prospective randomized crossover trial was performed, in which patients with suspected hilar/ mediastinal lymph node metastasis of lung cancer underwent EBUS-TBNA. The primary endpoint was the rate of yield histology specimens containing malignant cells.Results: From December 2018 to February 2020, 102 patients were randomly assigned to EBUS-TBNA using a 22G needle first, followed by a 25G needle (n=50) or EBUS-TBNA using a 25G needle first, followed by a 22G needle (n=52). There was no difference in the diagnostic yield of malignancy between the histology specimens obtained by using the 22G and 25G needles (75% vs. 75%, respectively, P=0.37). The sizes of the tissue samples (16.4 vs. 4.9 mm 2 , respectively) and number of malignant cells in the tissue samples (626 vs. 400, respectively) were both significantly higher when using the 22G needle than when using the 25G needle.Conclusions: No significant difference in the diagnostic yield between the 22G and 25G needles was observed for the diagnosis of lymph node metastasis of lung cancer, suggesting that needles of either gauge could be used for the biopsy. However, we would recommend use of the 22G needle, because it provided larger specimens and specimens containing larger numbers of malignant cells.

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<p>Legends of supplementary figure 1-7</p>