Potential Utility of a 4th-Generation EGFR-TKI and Exploration of Resistance Mechanisms-An In Vitro Study.

The emergence of acquired resistance to EGFR-tyrosine kinase inhibitors (TKIs) is almost inevitable even after a remarkable clinical response. Secondary mutations such as T790M and C797S are responsible for the resistance to 1st/2nd-generation (1/2G) TKIs and 3G TKIs, respectively. To overcome both the T790M and C797S mutations, novel 4G EGFR-TKIs are now under early clinical development. In this study, we evaluated the efficacy of a 4G EGFR-TKI in the treatment of lung cancer with EGFR mutation as well as explored resistance mechanisms to a 4G TKI. First, we compared the efficacies of seven TKIs including a 4G TKI, BI4020, against Ba/F3 cell models that simulate resistant tumors after front-line osimertinib treatment failure because of a secondary mutation. We also established acquired resistant cells to BI4020 by chronic drug exposure. Ba/F3 cells with an osimertinib-resistant secondary mutation were refractory to all 3G TKIs tested (alflutinib, lazertinib, rezivertinib, almonertinib, and befotertinib). BI4020 inhibited the growth of C797S-positive cells; however, it was not effective against L718Q-positive cells. Erlotinib was active against all Ba/F3 cells tested. In the analysis of resistance mechanisms of BI4020-resistant (BIR) cells, none harbored secondary EGFR mutations. HCC827BIR cells had MET gene amplification and were sensitive to a combination of capmatinib (MET-TKI) and BI4020. HCC4006BIR and H1975BIR cells exhibited epithelial-to-mesenchymal transition. This study suggests that erlotinib may be more suitable than 4G TKIs to overcome secondary mutations after front-line osimertinib. We found that off-target mechanisms that cause resistance to earlier-generation TKIs will also cause resistance to 4G TKIs.

Secondary Mutations of the EGFR Gene That Confer Resistance to Mobocertinib in EGFR Exon 20 Insertion.

INTRODUCTION: Approximately 10% of mutations in the EGFR gene in NSCLC are in-frame insertions in exon 20 (X20ins). These tumors usually do not respond to conventional EGFR tyrosine kinase inhibitors (TKIs). Several novel EGFR TKIs active for X20ins are in clinical development, including mobocertinib, which was recently approved by the U.S. Food and Drug Administration. However, acquired resistance during treatment with these TKIs still occurs as in the case of EGFR TKIs of earlier generations. METHODS: We chronically exposed murine pro-B-cell line cells transduced with the five most common X20ins (A763_Y764insFQEA, V769_D770insASV, D770_N771insSVD, H773_V774insNPH and H773_V774insH) to mobocertinib in the presence of N-ethyl-N-nitrosourea and searched for secondary EGFR mutations. We evaluated the efficacies of several EGFR X20ins inhibitors, including zipalertinib and sunvozertinib, against cells with acquired resistant mutations. RESULTS: All secondary mutations resulting in acquired resistance to mobocertinib were exclusively C797S in insFQEA and insSVD. However, in the case of other X20ins (insASV, insNPH, and insH), T790M or C797S secondary mutations contributed to acquired resistance to mobocertinib. The emergence of T790M was more frequent in cells treated with lower drug concentrations. Sunvozertinib exhibited good activity against resistant cells with T790M. Cells with C797S were refractory to all EGFR TKIs, except for erlotinib, which was active for insFQEA with C797S. CONCLUSIONS: T790M or C797S, depending on the original X20ins mutations, conferred acquired resistance to mobocertinib. Sunvozertinib may be the treatment of choice for patients with tumors resistant to mobocertinib because of T790M.

[A Case Report of Stage â £b Thoracic Esophageal Cancer Responding to Multidisciplinary Treatment].

A 68-year-old man was referred to our hospital because of back pain during swallowing. Upper gastrointestinal endoscopy revealed a lower esophageal type 3 tumor. The patient was diagnosed with esophageal squamous cell carcinoma by the biopsy specimen. CT scan showed thoracic lower esophagus wall thickening, left paracardiac lymph node swelling, and a low-density area in the liver. Therefore, the patient was diagnosed with Stage Ⅳb esophageal cancer. After introducing cisplatin plus 5-FU combination therapy, the liver metastasis disappeared. After 9 chemotherapy courses, the patient received radical chemoradiotherapy. After completing chemoradiotherapy, the patient was followed up without any treatment. After 3 years since the treatment initiation, the patient is surviving without any relapse.

[Case of Robot-Assisted Low Anterior Resection with Total Cystectomy for Rectal Cancer Invading the Urinary Bladder/Prostate in Collaboration with Urologists].

We present a case of a 72-year-old man diagnosed with rectal cancer invading the urinary bladder/prostate. Preoperative chemoradiotherapy substantially reduced the tumor size. In collaboration with urologists, robot-assisted low anterior resection with total cystectomy was performed using the da Vinci Xi system. Depending on the surgical situation, the colorectal surgeon and urologist could smoothly and rapidly play the role of a console surgeon. Although the first robot-assisted multi-organ resection of our institution, the surgery was completed safely without any complications. Although the patient developed urinary tract infection postoperatively, he recovered and was discharged after postoperative 23 days. In conclusion, robot-assisted surgery would be useful in pelvic surgery involving multiple departments such as colorectal surgery, urology, and gynecology.