Clinical Validity of Plasma-Based Genotyping for Microsatellite Instability Assessment in Advanced GI Cancers: SCRUM-Japan GOZILA Substudy.

PURPOSE: Circulating tumor DNA (ctDNA) genotyping may guide targeted therapy for patients with advanced GI cancers. However, no studies have validated ctDNA genotyping for microsatellite instability (MSI) assessment in comparison with a tissue-based standard. PATIENTS AND METHODS: The performance of plasma-based MSI assessment using Guardant360, a next-generation sequencing-based ctDNA assay, was compared with that of tissue-based MSI assessment using a validated polymerase chain reaction-based method in patients with advanced GI cancers enrolled in GOZILA study, a nationwide ctDNA profiling study. The primary end points were overall percent agreement, positive percent agreement (PPA), and negative percent agreement. The efficacy of immune checkpoint inhibitor therapy was also evaluated. RESULTS: In 658 patients with advanced GI cancers who underwent both plasma and tissue testing for MSI, the overall percent agreement, PPA, and negative percent agreement were 98.2% (95% CI, 96.8 to 99.1), 71.4% (95% CI, 47.8 to 88.7), and 99.1% (95% CI, 98.0 to 99.7), respectively. In patients whose plasma samples had a ctDNA fraction ≥ 1.0%, the PPA was 100.0% (15/15; 95% CI, 78.2 to 100.0). Three patients with MSI-high (MSI-H) tumors detected only by ctDNA genotyping achieved clinical benefits after receiving anti-programmed cell death 1 therapy with the progression-free survival ranging from 4.3 to 16.7 months. One patient with an aggressive cancer of an unknown primary site benefited from pembrolizumab after rapid detection of MSI-H by ctDNA genotyping. CONCLUSION: ctDNA genotyping was able to detect MSI with high concordance to validated tissue-based MSI testing, especially in patients with tumors that have sufficient ctDNA shedding. Furthermore, ctDNA genotyping enabled identification of patients with MSI-H tumors who benefited from immune checkpoint inhibitor treatment.

Endoscopic Evaluation of Neoadjuvant Chemotherapeutic Efficacy in Gastric Cancer before Gastrectomy Might be as Useful as Histological Assessment after Gastrectomy.

BACKGROUND: Neoadjuvant chemotherapy for advanced gastric cancer is expected to improve prognoses. However, as there is no method to evaluate neoadjuvant chemotherapeutic efficacy before gastrectomy, some patients at high risk for a poor prognosis undergo gastrectomy. The aim of the present study was to investigate whether endoscopy could be useful for assessing the efficacy of neoadjuvant chemotherapy. METHODS: In this retrospective study, we analyzed the data of 41 patients who received neoadjuvant chemotherapy followed by gastrectomy at our institution to investigate whether responsiveness to neoadjuvant chemotherapy, as assessed with endoscopy, can serve as a surrogate marker for histological grades 1b or higher in the Japanese Classification of Gastric Carcinoma (JCGC) scheme. RESULTS: There were 32 (78.0%) responders and 9 (22.0%) nonresponders to neoadjuvant chemotherapy, as observed in endoscopic evaluations. Among the endoscopic responders, 24 (75.0%) had cancer of histological grade 1b or higher, and 15 (46.9%) had cancer of grade 2 or higher. Among the endoscopic nonresponders, 1 (11.1%) patient had histological grade 1b cancer. Compared with endoscopic nonresponders, endoscopic responders were more likely to show a histological response (chi-square test: p = 0.0005 for JCGC grade 1b or higher; p = 0.0099 for JCGC grade 2 or higher). CONCLUSIONS: Most endoscopic responders showed JCGC histological responses. Evaluation of neoadjuvant chemotherapeutic efficacy by endoscopy in gastric cancer may be useful before gastrectomy. As this was a retrospective study, further investigations are required. The protocol was approved by the ethics review committee at Osaka Medical College (No. 2422) and was registered in the University Hospital Medical Information Network Clinical Trial Registry (UMIN000033088).