Masaya Nishino

EGFR T790M and C797S Mutations as Mechanisms of Acquired Resistance to Dacomitinib

Introduction: Dacomitinib was superior to gefitinib in terms of progression‐free survival in patients with EGFR‐mutant lung cancer in a recent ARCHER 1050 trial. However, despite a marked initial response, lung cancers eventually acquire resistance to these inhibitors. This study aimed to elucidate the mechanisms of acquired resistance to dacomitinib in vitro. Methods: Dacomitinib‐resistant clones were established by exposure to fixed concentrations of dacomitinib by using N‐ethyl‐N‐nitrosourea (ENU) mutagenesis or by chronic exposure to increasing concentrations of dacomitinib without ENU. EGFR secondary mutations were analyzed by Sanger sequencing. Time to resistance in each clone was compared according to the mutational status. EGFR Del19, L858R, and G719A mutations were introduced into Ba/F3 cells by using retroviral vectors. Results: Chronic exposure to dacomitinib without ENU induced T790M in Ba/F3 cells expressing Del19. ENU mutagenesis resulted in 171 dacomitinib‐resistant clones. Among these clones, 90% acquired T790M. However, C797S occurred in 11% of L858R‐mutant clones (four of 35) and in 24% of G719A‐mutant clones (12 of 38) established by using low‐dose dacomitinib. Time to resistance was not significantly different between T790M‐ and C797S‐mutant clones in both of L858R clones (p = 0.93) and G719A clones (p = 0.86). Cells expressing Del19 that acquired T790M were sensitive to osimertinib, whereas cells with L858R plus C797S mutations were sensitive to gefitinib or erlotinib. Conclusions: These in vitro data demonstrate that dacomitinib can directly induce T790M or C797S secondary mutations. Our data suggest the importance of analyzing these secondary mutations because appropriate selection of EGFR inhibitors could overcome acquired resistance to dacomitinib in a subset of lung cancers.

Clinical significance of tumor cavitation in surgically resected early-stage primary lung cancer

OBJECTIVES The prognostic impact of tumor cavitation is unclear in patients with early-stage primary lung cancer. The aim of the present study was to examine the clinicopathological features and prognoses of patients with pathological stage I-IIA (p-stage I-IIA) primary lung cancers harboring tumor cavitation. This study was conducted according to the eighth edition of the TNM classification for lung cancer. MATERIALS AND METHODS We examined 602 patients with p-stage I-IIA primary lung cancer out of 890 patients who underwent pulmonary resection from January 2007 through March 2014 and searched for the presence of tumor cavitation, which is defined as the presence of air space within the primary tumor. RESULTS A total of 59 out of the 602 patients had tumor cavitation (10%). Compared with patients without tumor cavitation, those with tumor cavitation had a significantly higher frequency of the following characteristics: high serum carcinoembryonic antigen (CEA) level (≥5ng/ml, p=0.027), interstitial pneumonia (p=0.0001), high SUVmax value on FDG-PET scan (≥4.2, p=0.023), tumors located in the lower lobe (p=0.024), large tumor size (>3cm, p=0.002), vascular invasion (66% vs 17%, p<0.0001) and non-adenocarcinoma histology (p=0.025). The overall survival period of patients with tumor cavitation was significantly shorter than that of patients without tumor cavitation (log-rank test: p<0.0001, 5-year OS rate: 56% vs 81%). Tumor cavitation was found to be an independent and significant factor associated with poor prognosis in the multivariate analysis (hazard ratio: 1.76, 95% confidence interval: 1.02-3.10, p=0.042). CONCLUSIONS Tumor cavitation is an independent factor for poor prognosis in patients with resected p-stage I-IIA primary lung cancer. Based on our analyses, patients with tumor cavitation should be regarded as a separate cohort that requires more intensive follow-up.

Prognostic impact of pleural lavage cytology in patients with primary lung cancer.

OBJECTIVES Positive pleural lavage cytology (PLC) has been reported to have a negative prognostic impact in patients with surgically resected non-small cell lung cancer (NSCLC). However, positive PLC does not upgrade the stage according to the 7th edition of TNM classification for lung cancer. The objectives of this study were to evaluate the prognostic impact of positive PLC in patients with NSCLC and to clarify its contribution to TNM classification. MATERIALS AND METHODS Seven hundred fifty-four patients who underwent surgical resection of NSCLC from January 2007 through December 2013 were retrospectively studied. PLC was performed using 50ml of saline immediately after thoracotomy. RESULTS Thirty-eight of the 754 patients were positive for PLC (5.1%). The overall survival (OS) of patients with positive PLC was significantly shorter than that of those with negative PLC (P=0.007, log-rank test). In multivariate analyses of OS, positive PLC was a significant independent prognostic factor (hazard ratio=2.21, 95% confidence interval: 1.21-4.04, P=0.009). The OS of patients with positive PLC was significantly shorter than that of those with negative PLC and pT1 (P<0.0001) or negative PLC and pT2 (P<0.0001) and almost overlapped with that of those with negative PLC and pT3 disease (P=0.601). CONCLUSION Positive PLC is an independent prognostic factor in patients with resected NSCLC. Based on our analyses, we propose that patients with positive PLC be staged as pT3.

Activity of a novel HER2 inhibitor, poziotinib, for HER2 exon 20 mutations in lung cancer and mechanism of acquired resistance: an in vitro study

OBJECTIVES Oncogenic HER2 mutations are present in 2-4% of lung adenocarcinomas, but the relevant clinical trials are unsatisfactory. The novel HER2 inhibitor poziotinib was recently developed and clinical trials are ongoing. We compared poziotinib with nine tyrosine kinase inhibitors (TKIs), and derived poziotinib-resistant clones to investigate the resistant mechanism. MATERIALS AND METHODS We introduced three common HER2 mutations A775_G776insYVMA (YVMA), G776delinsVC (VC) and P780_Y781insGSP (GSP), which account for 94% of HER2 exon 20 insertions in the literature, into Ba/F3 cells. We then compared the activity of poziotinib with that of nine TKIs (erlotinib, afatinib, dacomitinib, neratinib, osimertinib, AZ5104, pyrotinib, lapatinib, and irbinitinib), determined the 90% inhibitory concentration (IC90) through a growth inhibition assay, and defined a sensitivity index (SI) as IC90 divided by the trough concentration at the recommended dose as a surrogate for drug activity in humans. We also generated resistant clones by exposure to poziotinib in the presence of N-ethyl-N-nitrosourea, and HER2 secondary mutations that might serve as a resistance mechanism were searched. RESULTS YVMA showed resistance to all tested drugs except neratinib, poziotinib and pyrotinib. Poziotinib was the only drug with an SI less than 10 for YVMA, the most common HER2 exon 20 insertion. We established 62 poziotinib-resistant clones, and among these, only C805S of HER2, which is homologous to C797S of the EGFR, was identified as a secondary mutation in 19 clones. We also revealed that heat shock protein (HSP) 90 inhibitors show potent anti-growth activity to the C805S secondary mutant clone. CONCLUSIONS Poziotinib showed the most potent activity against HER2 exon 20 mutations. We identified the secondary C805S at the covalent binding site of HER2 to poziotinib as a potential mechanism of acquired resistance. HSP90 inhibitors might be a therapeutic strategy for the C805S secondary mutation.

Well-leg compartment syndrome after laparoscopic low anterior resection for lower rectal cancer in the lithotomy position: A case report

A 64‐year‐old man underwent laparoscopic low anterior resection for lower rectal cancer. Because he was overweight (BMI, 28.1 kg/m2) with rich visceral fat and a narrow pelvic cavity, the operation was technically difficult and the operation time was 686 min. Postoperatively, the patient immediately complained of pain and swelling of the left lower limb. Laboratory examination showed that serum creatinine kinase was markedly increased and urine myoglobin was positive on postoperative day 1. He was diagnosed with well‐leg compartment syndrome and was transported to the trauma and critical care center for emergency fasciotomy. After initial treatment, he was transferred to our hospital on postoperative day 7. He completely recovered after 2 months. Although well‐leg compartment syndrome is rare, it is necessary to consider it as a potential complication when performing a long colorectal cancer surgery with the patient in the lithotomy position, particularly when laparoscopic surgery is planned.