By monitoring real-time shifts in circulating tumour cells (CTCs) enumeration and HLA I and PD-L1 expression, with a focus on the longitudinal trajectory of their ratio, the study team from the University of Wisconsin-Madison in Madison, WI, US led by Dr. Shuang G. Zhao was able to capture new insights into metastatic renal cell carcinoma (mRCC) evolution to tyrosine kinase inhibitors (TKI) and immune checkpoint inhibitors (ICIs) and demonstrate their prognostic importance. Findings from the largest CTC study in mRCC which profiled 457 blood samples from 104 patients from a prospective institutional cohort and the phase II OMNIVORE immunotherapy study are published on 26 May 2022 in the Journal of Clinical Oncology.
The authors wrote in the background that capturing the molecular heterogeneity and complexity of the immune system and metastatic cancer burden through in vitro and in vivo model systems is challenging and the human studies are required. However, this presents its own challenges as tissue biopsies for molecular profiling of mRCC are invasive, logistically challenging to scale, and carry the risk of procedural complications.
Many of the landmark studies in mRCC have relied at least in part on archival nephrectomy specimens, which may not accurately reflect changes in the current tumour status because of time or treatment-induced alterations. Even when metastatic biopsies are available, the serial sampling required to understand real-time tumour evolution is not feasible and almost never performed. Liquid biopsies that assess CTCs represent a non-invasive alternative.
The study team collected 457 longitudinal liquid biopsies from 104 patients with mRCC enroled in one of two studies, either a prospective cohort or a phase II multicentre adaptive immunotherapy study. Using a novel CTC capture and automated microscopy platform, the study team profiled CTC enumeration and expression of HLA I and PD-L1. Given their diametric immunological roles, they focused on the HLA I to PD-L1 ratio.
Patients with radiographic responses showed significantly lower CTC abundances throughout treatment. Furthermore, patients whose CTC enumeration trajectory was in the highest quartile had shorter overall survival (OS) with median 17.0 months versus 21.1 months (p < 0.001). Throughout treatment, the HLA I to PD-L1 ratio decreased in patients receiving immunotherapy, but not in patients receiving TKIs. Patients with the HLA I to PD-L1 ratio trajectory in the highest quartile displayed significantly shorter OS with median 18.4 months versus 21.2 months (p = 0.003).
Past CTC studies in mRCC focused primarily on enumeration and demonstrated reduced OS with increased CTC abundance. By monitoring the real-time shifts in enumeration and the molecular profile of CTCs, the study was able to capture new insights into RCC evolution to therapy and demonstrate their prognostic importance.
The authors wrote that their study leverages the serial nature of liquid biopsies to demonstrate how biomarkers can be used to monitor patients over time, rather than just as a single snapshot. The trajectory of both CTC enumeration and the HLA I to PD-L1 ratio could provide guidance on a range of important treatment decisions such as when to initiate or change systemic therapy, especially in situations where imaging is ambiguous.
The authors also commented that their work forms the foundation for blood-based molecular profiling in RCC and potentially has implications for ICIs in other tumour types. Further validation of the clinical utility of these biomarkers requires testing in multiple large prospective clinical studies and this assay is being implemented as a correlative endpoint in a large multi-institutional prospective observational mRCC study, the recently approved randomised NRG SAMURAI study with ICI with or without radiation, and the randomised Alliance RadiCal study with TKI with or without Radium-223.
This work was funded by the US NIH and the Brian Mullins Renal Cell Cancer Research Award and other grants. The authors acknowledged the University of Wisconsin Carbone Cancer Center Biospecimen collection team and thanked also the staff of the University of Wisconsin Carbone Cancer Center Circulating Biomarker Core.
Bootsma M, McKay RR, Emamekhoo H, et al. Longitudinal Molecular Profiling of Circulating Tumor Cells in Metastatic Renal Cell Carcinoma. JCO; Published online 26 May 2022. DOI: 10.1200/JCO.22.00219