Transformation to small cell lung cancer is irrespective of EGFR and accelerated by SMAD4-mediated ASCL1 transcription independently of RB1 in non-small cell lung cancer.

OBJECTIVES: Histological transformation to small cell lung cancer (SCLC) has been identified as a mechanism of TKIs resistance in EGFR-mutant non-small cell lung cancer (NSCLC). We aim to explore the prevalence of transformation in EGFR-wildtype NSCLC and the mechanism of SCLC transformation, which are rarely understood. METHODS: We reviewed 1474 NSCLC patients to investigate the NSCLC-to-SCLC transformed cases and the basic clinical characteristics, driver gene status and disease course of them. To explore the potential functional genes in SCLC transformation, we obtained pre- and post-transformation specimens and subjected them to a multigene NGS panel involving 416 cancer-related genes. To validate the putative gene function, we established knocked-out models by CRISPR-Cas 9 in HCC827 and A549-TP53-/- cells and investigated the effects on tumor growth, drug sensitivity and neuroendocrine phenotype in vitro and in vivo. We also detected the expression level of protein and mRNA to explore the molecular mechanism involved. RESULTS: We firstly reported an incidence rate of 9.73% (11/113) of SCLC transformation in EGFR-wildtype NSCLC and demonstrated that SCLC transformation is irrespective of EGFR mutation status (P = 0.16). We sequenced 8 paired tumors and identified a series of mutant genes specially in transformed SCLC such as SMAD4, RICTOR and RET. We firstly demonstrated that SMAD4 deficiency can accelerate SCLC transition by inducing neuroendocrine phenotype regardless of RB1 status in TP53-deficient NSCLC cells. Further mechanical experiments identified the SMAD4 can regulate ASCL1 transcription competitively with Myc in NSCLC cells and Myc inhibitor acts as a potential subsequent treatment agent. CONCLUSIONS: Transformation to SCLC is irrespective of EFGR status and can be accelerated by SMAD4 in non-small cell lung cancer. Myc inhibitor acts as a potential therapeutic drug for SMAD4-mediated resistant lung cancer. Video Abstract.

Whole-exome sequencing explored mechanism of selpercatinib resistance in RET-rearranged lung adenocarcinoma transformation into small-cell lung cancer: a case report.

Small cell transformation was one mechanism by which EGFR-mutation NSCLC acquired resistance after tyrosine kinase inhibitors (TKIs) treatment. A few reports of small cell transformation occurred in other oncogene-driven lung cancers. We found the first case of transformation of a RET-rearranged lung adenocarcinoma to SCLC after selpercatinib, a novel highly selective RET TKIs. Whole-exome sequencing (WES) was used to explore alteration in gene expression in tumor tissue at initial diagnosis and after transformation into small cell carcinoma. We found that transformed into SCLC tumor tissue had inactivation of RB1 and TP53, with RET fusion was still present. In addition, the APOBEC family of cytidine deaminases appeared amplification. Although RET rearrangement still existed, using another RET TKIs was ineffective, and etoposide plus platinum might be an effective rescue treatment.

Transformation of Lung Squamous Cell Carcinoma to Small Cell Lung Cancer After Immunotherapy Resistance: A Case Report.

The transformation of lung adenocarcinoma to small cell lung cancer (SCLC) following treatment with epidermal growth factor (EGFR) receptor tyrosine kinase inhibitors (TKIs) is a relatively common phenomenon. However, transformation of non-small cell lung cancer (NSCLC) to SCLC following treatment with immunotherapy is very rare. Here, we report a case of a 56-year-old patient diagnosed with driver gene mutation-negative lung squamous cell carcinoma (SCC). He received four cycles of immunotherapy with sugemalimab and chemotherapy with albumin paclitaxel in combination with carboplatin, and a partial response was achieved. Subsequently, the patient received 5 cycles of immunotherapy with sugemalimab. However, he developed rapid progression of mediastinal lymph nodes, and biopsy results showed transformation to SCLC. His tumor did not respond to the next line of carboplatin combined with etoposide, and he died six months after the discovery of SCLC transformation. In conclusion, SCLC transformation is also an important resistance mechanism for lung SCC patients treated with immunotherapy and predicts a very poor outcome. Repeat biopsy is needed for advanced lung SCC that has progressed with immunotherapy.

First Report of Management of Sequential Small Cell Transformation and ALK I1171T Mutation as Resistance Mechanisms in a Patient With ALK-EML4 Fused Non-Small Cell Lung Adenocarcinoma With a Novel Combination of Temozolomide and Lorlatinib: A Case Report.

ALK-EML4 fusion-positive lung adenocarcinomas (LUADs) are effectively treated with ALK tyrosine kinase inhibitors, but most patients eventually develop resistance to these drugs owing to ALK-dependent or independent mechanisms. Endothelial to mesenchymal transformation with SCLC development is an ALK-independent mechanism of resistance that has not been previously reported with sequential ALK I1171T mutation while the patient is on treatment for the SCLC. Here, we report the first case of sequential SCLC transformation followed by ALK I1171T mutation in a patient with ALK-EML4 fusion-positive LUAD. After progression on multiple lines of therapy, we describe our experience of managing ALK-mutant LUAD and transformed SCLC with a novel combination of lorlatinib and temozolomide. We also briefly summarize cases of endothelial to mesenchymal transformation ALK-mutant LUAD from the literature.

Sequential small cell transformation and T790M mutation in an epidermal growth factor-mutant lung adenocarcinoma: A rare occurrence with significant management implications.

BACKGROUND: Epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI) resistance may be acquired via genotypic and/or phenotypic transformations. Herein, we report an extremely uncommon case with sequential small cell transformation and EGFR T790M mutation, in an elderly female with EGFR exon 21 L858R-mutant lung adenocarcinoma, following treatment with a first-generation EGFR-TKI. CASE: A 67-year-old female never-smoker presented with a cough and dyspnoea of 2 months' duration. Computerised tomography revealed a 39 mm lesion in the upper lobe of the right lung with pleural effusion. Pleural fluid cytology revealed metastatic lung adenocarcinoma, and EGFR testing revealed exon 21 L858R mutation. She was started on gefitinib. After a progression-free survival of 31 months, she presented with disease progression and multiple extra-thoracic metastases. Fine needle aspiration cytology of a chest wall lesion revealed metastatic small cell carcinoma. EGFR testing on this aspirate revealed persistent L858R mutation only. In view of small cell transformation, chemotherapy (etoposide and carboplatin) was administered. After 4 months, ascitic fluid cytology revealed metastatic adenocarcinoma with persistent L858R mutation and an acquired T790M mutation (both detected on liquid biopsy as well) indicating amplification of the adenocarcinoma clone and regression of the small cell carcinoma clone. She was then initiated on osimertinib. CONCLUSIONS: The index case highlights the significance of serial EGFR genotyping along with repeated tissue and/or blood sampling in the prompt detection of genetic and phenotypic resistance mechanisms to EGFR-TKIs. Furthermore, it lends evidence in support of the upfront treatment approaches targeting the heterogeneity of acquired EGFR-TKI resistance mechanisms.

Heterogeneity or transformation? A whack-a-mole case of EGFR-mutant lung adenocarcinoma and small cell carcinoma: A case report.

Histological transformation from adenocarcinoma to small cell lung cancer (SCLC) occurs ~10% after acquired resistance to epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors. Transformed SCLC generally responds well to chemotherapy regimens for SCLC such as platinum plus etoposide. After the response, histological nature and clinical course could be complicated by possible heterogeneity or transformation. Therefore, monitoring rebiospy is desirable to seize its histological nature at that moment. We report a case of EGFR-mutated adenocarcinoma, where histological transformations from adenocarcinoma and SCLC alternated. In this case, first rebiopsy after gefitinib revealed adenocarcinoma, but second rebiopsy after osimertinib identified SCLC transformation. After failure of platinum plus etoposide, adenocarcinoma-induced leptomeningeal metastases were controlled by osimertinib reintroduction. Optimal therapies could be provided according to the result of monitoring rebiopsy.

Small cell transformation of non-small cell lung cancer under immunotherapy: Case series and literature review.

In advanced lung cancer treatment, immunotherapy provides durable responses in some patients. However, other patients experience progressive disease and the resistance mechanisms to immunotherapy have yet been fully elucidated. Small cell transformation of non-small cell lung cancer (NSCLC) is commonly recognized as one of the resistance mechanisms to epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors in EGFR-mutant NSCLC treatment. As a resistant mechanism for immunotherapy, we report the first case of small cell transformation in 2017. Since then, eight similar cases have been reported and the concept of small cell transformation is now becoming more prevalent as a mechanism of immunotherapy resistance. In our facility, we have experienced four cases of small cell transformation after immunotherapy (including the reported case in 2017). The histology of each primary tumor was squamous cell carcinoma, large cell type neuroendocrine carcinoma, or poorly differentiated NSCLC. None had driver gene mutations. Nivolumab was administered in all four cases and atezolizumab was administered as a next line to nivolumab treatment in one case. The best response to immunotherapy was partial response or stable disease. There was a wide range of periods from the start of immunotherapy to confirmation of small cell transformation (from 2 weeks to almost 3 years). In conclusion, small cell transformation is an important resistance mechanism in cancer immunotherapy. When NSCLC progresses after immunotherapy, the possibility of small cell transformation and rebiopsy should always be encouraged, as it leads to clarification of the resistance mechanisms and frequency.

Small cell transformation in crizotinib-resistant ROS1-rearranged non-small cell lung cancer with retention of ROS1 fusion: A case report.

C-ros oncogene 1 receptor tyrosine kinase (ROS1) rearrangement has been detected in patients with advanced non-small cell lung cancer (NSCLC). Although ROS1 tyrosine kinase inhibitors (TKIs) provide a survival benefit for patients with ROS1-rearranged advanced NSCLC, subsequent therapy remains limited. Small cell transformation is an important mechanism of drug resistance in epidermal growth factor receptor-mutant NSCLC. However, its significance in mediating ROS1 resistance has not been determined yet. Here, we present the case of a 63-year-old man with ROS1-rearranged advanced NSCLC who had disease progression with small cell transformation of the mediastinal lymph node after 8 months of treatment with crizotinib. More importantly, fluorescence in situ hybridization of post-progression tumor biopsy demonstrated retention of ROS1 rearrangement. Tissue biopsy remains indispensable for patients who acquire resistance to ROS1 TKIs.

Alectinib re-challenge in small cell lung cancer transformation after chemotherapy failure in a patient with ALK-positive lung cancer: A case report.

Small cell lung cancer (SCLC) transformation is a rare resistance mechanism to anaplastic lymphoma kinase-tyrosine kinase inhibitors (ALK-TKIs), for which cytotoxic chemotherapy is often initiated. However, no case has been reported so far in which the SCLC component disappeared after chemotherapy and the tumor responded to ALK-TKI treatment again. A 41-year-old, never-smoker man was diagnosed with multiple metastatic lung adenocarcinoma harboring ALK gene rearrangements. After tumor re-growth was treated with alectinib, histological analysis of re-biopsy of the primary lesion showed combined small cell carcinoma, and cytotoxic chemotherapy was administered. After resistance to chemotherapy developed, the third biopsy of the primary lesion showed the original ALK gene rearrangements without the SCLC component. Alectinib was re-administered, and partial response was obtained. Biopsy for ALK-positive lung cancer that progressed after chemotherapy for SCLC transformation might be useful for decision-making regarding the therapeutic strategy.

Primary resistance to osimertinib despite acquired T790M.

Current National Comprehensive Cancer Network (NCCN) guidelines suggest plasma-based testing (liquid biopsy) for T790M in epidermal growth factor receptor (EGFR)-mutated non-small cell lung carcinoma (NSCLC) with acquired resistance to first-/second-generation EGFR tyrosine kinase inhibitors (TKIs). Positivity for resistant mutation on liquid biopsy may obviate the need for invasive tissue biopsy. We report a rare case of primary resistance to osimertinib, although liquid biopsy revealed EGFR T790M positivity. A 63-year-old male, never smoker, was diagnosed with stage IV lung adenocarcinoma with EGFR exon 19 deletion. Treatment started with erlotinib and was continued for 15 months until disease progression. Osimertinib was initiated when liquid biopsy showed EGFR T790M positivity. However, primary resistance to osimertinib was noted on follow-up imaging. Re-biopsy revealed small cell lung cancer. Detection of T790M via liquid biopsy among NSCLC patients with acquired resistance to EGFR-TKI might miss other possible resistant mechanisms. Tissue biopsy should be considered to exclude small cell lung carcinoma (SCLC) transformation.

Transformation to small cell lung cancer as a mechanism of resistance to immunotherapy in non-small cell lung cancer.

OBJECTIVES: Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related death world-wide. Immune checkpoint inhibitors (ICI) have become the most promising type of treatment in oncology in general, and significantly so in NSCLC. Limited data is available about mechanisms of primary resistance. Data is lacking about mechanisms involved in acquired resistance or mixed responses in NSCLC. We aimed to identify mechanisms of resistance by studying biopsies taken from sites of secondary progression. MATERIALS AND METHODS: We identified all cases of NSCLC that have received ICI for advanced disease in our institute. Of these cases, those that have demonstrated acquired resistance or mixed responses, and have underwent a biopsy from a progressive lesion were analyzed. Selected specimens were subjected to next-generation sequencing (NGS; Oncomine™ Solid Tumour Fusion Transcript Kit). RESULTS: Out of 664 lung cancer cases, 249 were NSCLC that have received ICI. Of these, eight cases matched our search criteria. Two of them demonstrated transformation to small cell lung cancer (SCLC; 2/8, 25%). NGS verified a common origin to a matched pre-treatment NSCLC specimen and an on-treatment progressive SCLC specimen. In two cases no tumor cells were found and in the remaining four the pathology was similar to the initial biopsy. In one of the cases of SCLC transformation platinum-etoposide chemotherapy was administered, with short-term benefit only and further disease progression. CONCLUSION: Mechanisms of acquired resistance to ICI include SCLC transformation. Repeat biopsies of progressing lesions after initial response or in cases of mixed response can shed light on mechanisms of resistance.

Clinicopathological and genomic comparisons between different histologic components in combined small cell lung cancer and non-small cell lung cancer.

OBJECTIVE: Histologic transformation from adenocarcinoma to small cell lung cancer (SCLC) is one of the mechanisms of acquired resistance after epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) treatment. Furthermore, de novo combined SCLC/non-small cell lung cancer (NSCLC) have occasionally been reported; however, their mutational statuses and clinicopathological features have not yet been elucidated. In this study, we aimed to profile the genetic backgrounds of these 2 different histologic components by investigating patients with de novo combined SCLC/NSCLC as well as those with lung adenocarcinoma who experienced SCLC transformation after TKI treatment. MATERIALS AND METHODS: Four patients with de novo combined SCLC/NSCLC were investigated, as were 4 other patients with lung adenocarcinoma who experienced SCLC transformation after TKI treatment. The different histologic components of the tumors in each patient were tested for thyroid transcription factor-1, p40, synaptophysin, chromogranin A, p53, retinoblastoma protein (Rb), and achaete-scute homolog 1 (ASCL1) via immunohistochemistry, and were macroscopically dissected for mutational analysis using next-generation sequencing with the Oncomine Focus Assay and Comprehensive Assay panel. RESULTS: The distinct histologic components in patients with de novo combined SCLC/NSCLC and those with adenocarcinoma exhibiting small cell transformation showed high consistency in EGFR/TP53/RB1 mutations, and expression patterns of p53 and Rb. A high frequency of activating mutations involving PI3K/AKT1 signaling pathway was observed in SCLC. Nuclear ASCL1 expression was present in SCLC but absent or barely present in adenocarcinoma in 7 cases. CONCLUSIONS: Our data imply that inactivation of TP53/RB1 function is a possible early event in the histogenesis of synchronous and metachronous SCLC/NSCLC. Moreover, the non-adenocarcinoma (SCLC) component might arise from the adenocarcinoma (NSCLC) component through a mechanism that involves the activation of the ASCL1 and PI3K/AKT1 signaling pathways.

Role of chemotherapy with epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) rechallenge in small cell transformation after EGFR-TKI failure: a case report.

BACKGROUND: Small cell lung cancer (SCLC) transformation is one of the resistance mechanisms associated with epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs). Rechallenge with the first-line TKI after the second-line chemotherapy is suggested as a salvage treatment despite modest efficacy. CASE PRESENTATION: Here, we report the case of a 72-year-old, never-smoker female diagnosed with multiple metastatic lung adenocarcinoma (cT2aN2M1) harboring EGFR mutations in exon 21 (L858R) of the primary lesion. Despite subsequent treatment with gefitinib for more than a year, the patient developed resistance to the drug. Histological analysis based on rebiopsy at subphrenic mass revealed small cell transformation. After a partial response to irinotecan and carboplatin, the metastatic subphrenic and liver masses presented dramatic progression despite another round of cytotoxic chemotherapy. Rechallenge with erlotinib based on the original EGFR mutation (L858R) without small cell transformation confirmed by re-biopsy of hepatic mass lesions elicited only mixed response. Therefore, cytotoxic chemotherapy comprising irinotecan and carboplatin combined with erlotinib was effective against all the metastatic lesions. CONCLUSION: To the best of our knowledge, this is the first case of concurrent retreatments with TKIs and chemotherapy previously effective in SCLC transformation.

Molecular mechanisms of therapy resistance in solid tumors: chasing "moving" targets.

The goal of personalized cancer therapy is to treat tumors based on genomic aberrations that drive their survival and progression. Most patients who receive targeted therapies typically develop resistance and disease progression within a year's time. This review focuses on the heterogeneous mechanisms of therapy resistance to tyrosine kinase inhibitors, endocrine/hormone therapy and checkpoint blockade using non-small cell lung cancer, breast and castration-resistant prostate cancer, and melanoma as classical examples, respectively. In addition, testing for resistance mechanisms and therapeutic approaches to overcoming resistance is addressed.