Transformation of advanced lung adenocarcinoma to acquired T790M resistance mutation adenosquamous carcinoma following tyrosine kinase inhibitor: a case report

Clonal dynamics and Stereo-seq resolve origin and phenotypic plasticity of adenosquamous carcinoma

The genomic origin and development of the biphasic lung adenosquamous carcinoma (ASC) remain inconclusive. Here, we derived potential evolutionary trajectory of ASC through whole-exome sequencing, Stereo-seq, and patient-derived xenografts. We showed that EGFR and MET activating mutations were the main drivers in ASCs. Phylogenetically, these drivers and passenger mutations found in both components were trunk clonal events, confirming monoclonal origination. Comparison of multiple lesions also revealed closer genomic distance between lymph node metastases and the ASC component with the same phenotype. However, as mutational signatures of EGFR-positive lung squamous carcinomas (LUSCs) were more comparable to EGFR-positive ASCs than to wild-type LUSCs, we postulated different origination of these LUSCs, with ASC being the potential intermediate state of driver-positive LUSCs. Spatial transcriptomic profiling inferred transformation from adenocarcinoma to squamous cell carcinoma, which was then histologically captured in vivo. Together, our results explained the development of ASC and provided insights into future clinical decisions.

The current state of the art and future trends in RAS-targeted cancer therapies

Despite being the most frequently altered oncogenic protein in solid tumours, KRAS has historically been considered ‘undruggable’ owing to a lack of pharmacologically targetable pockets within the mutant isoforms. However, improvements in drug design have culminated in the development of inhibitors that are selective for mutant KRAS in its active or inactive state. Some of these inhibitors have proven efficacy in patients with KRAS^G12C-mutant cancers and have become practice changing. The excitement associated with these advances has been tempered by drug resistance, which limits the depth and/or duration of responses to these agents. Improvements in our understanding of RAS signalling in cancer cells and in the tumour microenvironment suggest the potential for several novel combination therapies, which are now being explored in clinical trials. Herein, we provide an overview of the RAS pathway and review the development and current status of therapeutic strategies for targeting oncogenic RAS, as well as their potential to improve outcomes in patients with RAS-mutant malignancies. We then discuss challenges presented by resistance mechanisms and strategies by which they could potentially be overcome.

The RAS oncogenes are among the most common drivers of tumour development and progression but have historically been considered undruggable. The development of direct KRAS inhibitors has changed this paradigm, although currently clinical use of these novel therapeutics is limited to a select subset of patients, and intrinsic or acquired resistance presents an inevitable challenge to cure. Herein, the authors provide an overview of the RAS pathway in cancer and review the ongoing efforts to develop effective therapeutic strategies for RAS-mutant cancers. They also discuss the current understanding of mechanisms of resistance to direct KRAS inhibitors and strategies by which they might be overcome.

Owing to intrinsic and extrinsic factors, KRAS and other RAS isoforms have until recently been impervious to targeting with small-molecule inhibitors.

Inhibitors of the KRAS^G12C variant constitute a potential breakthrough in the treatment of many cancer types, particularly non-small-cell lung cancer, for which such an agent has been approved by the FDA.

Several forms of resistance to KRAS inhibitors have been defined, including primary, adaptive and acquired resistance; these resistance mechanisms are being targeted in studies that combine KRAS inhibitors with inhibitors of horizontal or vertical signalling pathways.

Mutant KRAS has important effects on the tumour microenvironment, including the immunological milieu; these effects must be considered to fully understand resistance to KRAS inhibitors and when designing novel treatment strategies.

Case Report: Durable partial response to icotinib plus crizotinib in a lung adenocarcinoma patient with double uncommon EGFR G719D/L861Q mutations and an acquired novel CUX1-MET fusion

Non-small cell lung cancer (NSCLC) patients harboring MET exon 14 skipping or high MET amplification display a high rate of response to MET inhibitors. However, MET fusions in NSCLC have rarely been revealed. In this report, a 63-year-old woman with lung adenocarcinoma (LADC), harboring EGFR exon 18 G719D and exon 21 L861Q mutations, received first-generation, EGFR-tyrosine kinase inhibitor (TKI) icotinib therapy. Next generation sequencing (NGS) results only displayed an EGFR T790M point mutation following icotinib resistance. Thus, the patient was treated with osimertinib and achieved a stable disease (SD). However, disease progressed after 15 months and a novel MET fusion (CUX1 exon14-MET exon15) in addition to EGFR G719D/L861Q mutations were simultaneously detected in a tissue biopsy sample. After more than nine months, the patient subsequently achieved a PR with the combination of icotinib and crizotinib. To our knowledge, this is the first case of LADC patient displaying the presence of EGFR double uncommon mutations and an acquired novel CUX1-MET fusion that has benefited from icotinib plus crizotinib treatment. Following nine months of PR with icotinib plus crizotinib, the patient, until the time of publication, is exhibiting stable disease. The results suggest that the CUX1-MET fusion may be sensitive to crizotinib, although previous reports indicated that some MET fusion cases did not respond to crizotinib. Given this disparity, distinguishing MET fusion partners when crizotinib is used in LADC treatment is also very important.