Faculty Bibliography

INTRODUCTION/BACKGROUND:Microsatellite instability (MSI) testing and tumor mutational burden (TMB) are genomic biomarkers used to identify patients who are likely to benefit from immune checkpoint inhibitors. Pembrolizumab was recently approved by the Food and Drug Administration for use in TMB-high (TMB-H) tumors, regardless of histology, based on KEYNOTE-158. The primary objective of this retrospective study was real-world applicability and use of immunotherapy in TMB/MSI-high patients to lend credence to and refine this biomarker. METHODS:Charts of patients with advanced solid tumors who had MSI/TMB status determined by next generation sequencing (NGS) (FoundationOne CDx) were reviewed. Demographics, diagnosis, treatment history, and overall response rate (ORR) were abstracted. Progression-free survival (PFS) was determined from Kaplan-Meier curves. PFS1 (chemotherapy PFS) and PFS2 (immunotherapy PFS) were determined for patients who received immunotherapy after progressing on chemotherapy. The median PFS2/PFS1 ratio was recorded. RESULTS:MSI-high or TMB-H [≥20 mutations per megabase (mut/MB)] was detected in 157 adults with a total of 27 distinct tumor histologies. Median turnaround time for NGS was 73 days. ORR for most recent chemotherapy was 34.4%. ORR for immunotherapy was 55.9%. Median PFS for patients who received chemotherapy versus immunotherapy was 6.75 months (95% confidence interval, 3.9-10.9 months) and 24.2 months (95% confidence interval, 9.6 months to not reached), respectively (P = 0.042). Median PFS2/PFS1 ratio was 4.7 in favor of immunotherapy. CONCLUSION/CONCLUSIONS:This real-world study reinforces the use of TMB as a predictive biomarker. Barriers exist to the timely implementation of NGS-based biomarkers and more data are needed to raise awareness about the clinical utility of TMB. Clinicians should consider treating TMB-H patients with immunotherapy regardless of their histology.

Locally advanced rectal cancer has broadly been defined as T3, T4, or lymph node-positive disease. In the 1990s, adjuvant chemoradiation was considered the optimal management for locally advanced rectal cancer. However, the paradigm shifted when the German CAO/ARO/AIO-94 Rectal Cancer trial established neoadjuvant chemoradiation as the standard of care, based on reduced rates of toxicity and local recurrence, as well as higher rates of sphincter preservation compared with postoperative chemoradiation. Both short-course radiation and long-course chemoradiation are currently accepted methods for neoadjuvant treatment, with recent trials showing equivalence in outcomes. While surgery remains the cornerstone of treatment, there are data supporting the use of magnetic resonance imaging for risk stratification in rectal cancer and encouraging prospective data regarding nonoperative management. This review summarizes data on the evolution of treatment for locally advanced rectal cancer and discusses emerging evidence for nonoperative management.