Small-Cell Lung Cancer Transformation as a Mechanism of Resistance to Pralsetinib in RET-Rearranged Lung Adenocarcinoma: A Case Report

Rearranged during transfection (RET) lung cancer - Update on targeted therapies

The enhanced comprehension of the molecular pathways underpinning oncogenesis in non-small cell lung cancer (NSCLC) has led to the advancement of personalized treatment for individuals with actionable mutations using targeted therapies. The rearranged during transfection (RET) proto-oncogene, is critical in the embryonic development of various tissues, including renal, neural, and neuroendocrine tissue. RET fusions have been observed in approximately 1-2% of NSCLC cases. Targeted therapies for NSCLC with RET alterations have progressed significantly over the past decade. While multikinase inhibitors (MKIs) faced limitations in efficacy and tolerability, the introduction of selective RET inhibitors (SRIs) such as selpercatininb and pralsetinib has transformed patient outcomes, resulting in deep and durable responses. Ongoing clinical trials are exploring their potential benefits in the neoadjuvant and adjuvant setting. Early phase clinical trials endeavor to demonstrate next-generation selective RET inhibitors can effectively overcome SRI resistance mechanisms, offer improved safety profiles, and enhance patient outcomes.

Patients outcomes in lung adenocarcinoma transforming to small-cell lung cancer after tyrosine kinase inhibitor therapy

BACKGROUND

Non-small cell lung cancer (NSCLC) transforming to small cell lung cancer (SCLC) is one of the mechanisms of resistance to tyrosine kinase inhibitors (TKIs). Cases of NSCLC transforming into SCLC have been discovered. However, we lack concentrated data on the characteristics of this population and the transformed SCLC to aid our insight of the biology and clinical value of NSCLC transforming with positive.

METHODS

We systematically reviewed the published literatures and summarized the pathological and clinical characteristics, and the prognosis, of published cases.

RESULTS

140 patients with lung adenocarcinoma (LUAD) were included in this study, with a median age of 56.8 years. The median time from the first diagnosis of LUAD transforming to SCLC (ttSCLC) was 20.0 months. The median overall survival (mOS) after the diagnosis of SCLC was 11.0 months (95% CI, 7.41 to 14.59 months). In the univariate analysis, ever smoking (either former or current) was a promising predictor of a shorter ttSCLC (HR, 1.73; 95% CI, 1.14 to 2.62; P = 0.010). TKIs therapy administered as a second line and beyond treatment was related to a significant delay in SCLC onset compared to first-line therapy (HR, 0.62; 95% CI, 0.40 to 0.96; P = 0.031). The median progression-free survival (mPFS) on first-line platinum plus etoposide after the conversion to SCLC was 3.0 months. Female appeared to be related to worse outcomes after transformation of SCLC.

CONCLUSION

Transformed SCLC exhibited poor response to primary SCLC classic chemotherapy and immunotherapy. It carries a worse prognosis. Exploring novel therapeutic strategies for transformed SCLC is imperative.

Neuroendocrine Transformation as a Mechanism of Resistance to Targeted Lung Cancer Therapies: Emerging Mechanisms and Their Therapeutic Implications

Lung cancer is the leading cause of cancer-related deaths worldwide, highlighting a major clinical challenge. Lung cancer is broadly classified into two histologically distinct subtypes, termed small cell lung cancer (SCLC) or non-small cell lung cancer (NSCLC). Identification of various oncogenic drivers of NSCLC has facilitated the development of targeted therapies that have dramatically improved patient outcomes. However, acquired resistance to these targeted therapies is common, which ultimately results in patient relapse. Several on-target and off-target resistance mechanisms have been described for targeted therapies in NSCLC. One common off-target mechanism of resistance to these therapies is histological transformation of the initial NSCLC into SCLC, a highly aggressive form of lung cancer that exhibits neuroendocrine histology. This mechanism of resistance presents a significant clinical challenge, since there are very few treatments available for these relapsed patients. Although the phenomenon of NSCLC-to-SCLC transformation was described almost 20 years ago, only recently have we begun to understand the mechanisms underlying this therapy-driven response. These recent discoveries will be key to identifying novel biomarkers and therapeutic strategies to improve outcomes of patients that undergo NSCLC-to-SCLC transformation. Here, we highlight these recent advances and discuss the potential therapeutic strategies that they have uncovered to target this mechanism of resistance.

Real-World Outcomes of Pralsetinib in RET Fusion-Positive NSCLC

Introduction

Pralsetinib is a RET inhibitor found to have antitumor activity in advanced, metastatic, RET fusion-positive NSCLC.

Objective

To assess real-world efficacy of pralsetinib and treatment sequences in patients with RET fusion-positive NSCLC.

Design

Retrospective study of consecutive patients enrolled in the French expanded-access program for pralsetinib from December 1, 2019, to December 31, 2021.

Participants

A total of 41 patients with advanced, refractory, RET fusion-positive NSCLC were included. Pralsetinib was administered at a daily dose of 400 mg based on safety and pharmacokinetic outcomes from previous phase 1/2 study.

Results

Pralsetinib was administered as second line in 23 patients (56%) and as third line and beyond in 15 patients (37%). After a median follow-up of 26.3 months, pralsetinib was ongoing in 13 patients. Median real-world progression-free survival was 11.8 (95% confidence interval [CI]: 9.3-15.5) months. Objective response rate was 68% (95% CI: 50%-82%), and disease control rate was 89% (95% CI: 75%-97%). Subsequent line of systemic therapy was initiated in 11 patients. Median overall survival from pralsetinib initiation was 23.8 (95% CI: 16.5-not reached) months.

Conclusion

In this extensive real-world cohort of patients with advanced or metastatic NSCLC harboring RET fusions, we highlight the antitumor efficacy of pralsetinib, particularly when administered in later treatment lines. We also observe the aggressive nature of disease progression, frequent utilization of chemotherapy and antiangiogenic agents as initial subsequent therapies, and limited insight into resistance mechanisms due to infrequent rebiopsy and genomic profiling at progression.

RET Inhibitors in RET Fusion-Positive Lung Cancers: Past, Present, and Future

While activating RET fusions are identified in various cancers, lung cancer represents the most common RET fusion-positive tumor. The clinical drug development of RET inhibitors in RET fusion-positive lung cancers naturally began after RET fusions were first identified in patient tumor samples in 2011, and thereafter paralleled drug development in RET fusion-positive thyroid cancers. Multikinase inhibitors were initially tested with limited efficacy and substantial toxicity. RET inhibitors were then designed with improved selectivity, central nervous system penetrance, and activity against RET fusions and most RET mutations, including resistance mutations. Owing their success to these rationally designed features, the first-generation selective RET tyrosine kinase inhibitors (TKIs) had higher response rates, more durable disease control, and an improved safety profile compared to the multikinase inhibitors. This led to lung and thyroid cancer, and later tumor-agnostic regulatory approvals. While next-generation RET TKIs were designed to abrogate uncommon on-target (e.g., solvent front mutation) resistance to selpercatinib and pralsetinib, many of these drugs lacked the selectivity of the first-generation TKIs, raising the question of what the future holds for drug development in RET-dependent cancers.

Potential therapeutic option for EGFR-mutant small cell lung cancer transformation: a case report and literature review

Transformation from non-small cell lung cancer (NSCLC) to small cell lung cancer (SCLC) is rare and is associated with poor prognosis. However, the standard treatment protocols for patients with SCLC transformation remain unknown. Here, we report the case of a patient with advanced EGFR exon 19 deletion (19del) NSCLC who underwent SCLC transformation during targeted therapy. Biopsies and genetic testing were performed to adjust treatment regimens accordingly. The patient responded favorably to a combined treatment regimen comprising etoposide plus cisplatin chemotherapy and adebrelimab plus osimertinib. This case highlights the critical importance of acknowledging tumor heterogeneity in clinical decision-making and identifying potentially effective treatment options for patients with SCLC transformation. Additionally, we reviewed cases of the transformation of NSCLC to SCLC from 2017 to 2023.

Small cell lung cancer: emerging subtypes, signaling pathways, and therapeutic vulnerabilities

Small cell lung cancer (SCLC) is a recalcitrant cancer characterized by early metastasis, rapid tumor growth and poor prognosis. In recent decades, the epidemiology, initiation and mutation characteristics of SCLC, as well as abnormal signaling pathways contributing to its progression, have been widely studied. Despite extensive investigation, fewer drugs have been approved for SCLC. Recent advancements in multi-omics studies have revealed diverse classifications of SCLC that are featured by distinct characteristics and therapeutic vulnerabilities. With the accumulation of SCLC samples, different subtypes of SCLC and specific treatments for these subtypes were further explored. The identification of different molecular subtypes has opened up novel avenues for the treatment of SCLC; however, the inconsistent and uncertain classification of SCLC has hindered the translation from basic research to clinical applications. Therefore, a comprehensives review is essential to conclude these emerging subtypes and related drugs targeting specific therapeutic vulnerabilities within abnormal signaling pathways. In this current review, we summarized the epidemiology, risk factors, mutation characteristics of and classification, related molecular pathways and treatments for SCLC. We hope that this review will facilitate the translation of molecular subtyping of SCLC from theory to clinical application.

Novel therapeutic strategies targeting bypass pathways and mitochondrial dysfunction to combat resistance to RET inhibitors in NSCLC

RET fusion is an oncogenic driver in 1-2 % of patients with non-small cell lung cancer (NSCLC). Although RET-positive tumors have been treated with multikinase inhibitors such as vandetanib or RET-selective inhibitors, ultimately resistance to them develops. Here we established vandetanib resistance (VR) clones from LC-2/ad cells harboring CCDC6-RET fusion and explored the molecular mechanism of the resistance. Each VR clone had a distinct phenotype, implying they had acquired resistance via different mechanisms. Consistently, whole exome-seq and RNA-seq revealed that the VR clones had unique mutational signatures and expression profiles, and shared only a few common remarkable events. AXL and IGF-1R were activated as bypass pathway in different VR clones, and sensitive to a combination of RET and AXL inhibitors or IGF-1R inhibitors, respectively. SMARCA4 loss was also found in a particular VR clone and 55 % of post-TKI lung tumor tissues, being correlated with higher sensitivity to SMARCA4/SMARCA2 dual inhibition and shorter PFS after subsequent treatments. Finally, we detected an increased number of damaged mitochondria in one VR clone, which conferred sensitivity to mitochondrial electron transfer chain inhibitors. Increased mitochondria were also observed in post-TKI biopsy specimens in 13/20 cases of NSCLC, suggesting a potential strategy targeting mitochondria to treat resistant tumors. Our data propose new promising therapeutic options to combat resistance to RET inhibitors in NSCLC.

Histologic transformation of non-small-cell lung cancer in response to tyrosine kinase inhibitors: Current knowledge of genetic changes and molecular mechanisms

Lung cancer is the leading cause of cancer death and includes two major types: non-small-cell lung cancer (NSCLC) and small-cell lung cancer (SCLC), accounting for 85% and 15% of cases, respectively. Non-small-cell lung cancer harboring actionable driver mutations is generally treated with tyrosine kinase inhibitors (TKIs) molecularly targeting individual oncogenes. Although TKIs have greatly contributed to better clinical outcomes, acquired resistance to them inevitably occurs. Histologic or lineage transformation is a rare but well-documented off-target mechanism associated with acquired resistance, and has been identified in settings following treatment with multiple different TKIs and other drugs. It includes neuroendocrine transformation, squamous cell transformation, and epithelial-to-mesenchymal transition. Here, we review the clinicopathologic features of transformed tumors and current understanding of the key genetic alterations and biologic mechanism of lineage transformation in NSCLC, particularly TKI-triggered transformation.

ALK-rearranged and EGFR wild-type lung adenocarcinoma transformed to small cell lung cancer: a case report

Background

Cases of ALK-rearranged EGFR wild-type lung adenocarcinoma (LUAD) transforming into small cell lung cancer (SCLC) are rarely reported, and diagnosis is often delayed. The emergence of this transformation phenomenon is often regarded as a consequence of acquired resistance mechanisms.

Case presentation

A 47-year-old male diagnosed with poorly differentiated adenocarcinoma of the right middle lung (pT2N2M0, stage IIIA) achieved a 46-month progression-free survival (PFS) following surgery and adjuvant chemotherapy. During routine follow-up, tumor recurrence and metastasis was detected. Genetic testing revealed ALK rearrangement and wild-type EGFR, prompting treatment with ALK-TKIs. In May 2023, abdominal CT scans showed significant progression of liver metastases and abnormal elevation of the tumor marker NSE. Immunohistochemical results from percutaneous liver biopsy indicated metastatic SCLC.

Results

After resistance to ALK-TKIs and transformation to SCLC, the patient received chemotherapy combined with immunotherapy for SCLC, but the patient's disease progressed rapidly. Currently, the patient is being treated with albumin-bound paclitaxel in combination with oral erlotinib and remains stable.

Conclusion

Histological transformation emerges as a compelling mechanism of resistance to ALK-TKIs, necessitating the utmost urgency for repeat biopsies in patients displaying disease progression after resistance. These biopsies are pivotal in enabling the tailor-made adaptation of treatment regimens to effectively counteract the assorted mechanisms of acquired resistance, thus optimizing patient outcomes in the battle against ALK-driven malignancies.

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.

Addition of Trastuzumab Deruxtecan to Selpercatinib in a Patient With RET Fusion-Driven NSCLC and an Acquired HER2 Amplification: Case Report

Despite the high activity of selective RET inhibitors in RET-driven NSCLC, resistance eventually develops and there is unmet need to better define therapeutic options for patients. This is a case of a patient initially thought to have no targetable alterations, then found to have a RET fusion, and subsequently HER2 amplification on three distinct biopsies. She was treated initially with chemotherapy and immune therapy, then switched to selpercatinib, and eventually had fam-trastuzumab deruxtecan added to selpercatinib. She also developed neuroendocrine differentiation at time of progression in the context of a p53 mutation, which is a known factor that can lead to small cell transformation. This patient's case highlights the need for comprehensive molecular testing at both diagnosis and progression, as unexpected resistance mechanisms may be identified particularly for patients with uncommon driver mutations.

Establishment and characterization of BMC-PDC-019: a novel patient-derived cell line of EGFR-mutant pulmonary adenocarcinoma transformed into small-cell lung cancer

Transformed small-cell lung cancer (tSCLC) from EGFR-mutant adenocarcinoma is a rare and aggressive form of lung cancer that can occur when the tumor develops resistance to EGFR targeted therapy and the cancer cells acquire additional genomic alterations that cause them to transform into SCLC. Treatment for tSCLC has not been established yet, and chemotherapy regimens for de novo SCLC are mostly recommended. However, these treatments showed disappointing outcome, and novel anti-cancer agents and immunological approaches are currently being developed. The patient-derived cell line is a critical tool for pre-clinical and translational research, but cell line models for tSCLC are not publicly available from cell banks. The aim of this study was to establish and characterize a novel cell line for tSCLC. Using a lymph-node biopsy tissue from a 58-year-old female patient, whose tumor was EGFR-mutant lung adenocarcinoma progressed on afatinib, we successfully established a cell line, named BMC-PDC-019. The tumor sample and cell line showed a typical expression of SCLC markers, such as CD56 and synaptophysin. The population doubling-time of BMC-PDC-019 cells was 48 h. We examined a range of proliferation-inhibiting effects of anti-cancer drugs currently used for de novo SCLC, using BMC-PDC-019 cells. We concluded that BMC-PDC-019 would be a useful tool for pre-clinical and translational research.

Expert consensus on the diagnosis and treatment of RET gene fusion non-small cell lung cancer in China

The rearranged during transfection (RET) gene is one of the receptor tyrosine kinases and cell-surface molecules responsible for transmitting signals that regulate cell growth and differentiation. In non-small cell lung cancer (NSCLC), RET fusion is a rare driver gene alteration associated with a poor prognosis. Fortunately, two selective RET inhibitors (sRETi), namely pralsetinib and selpercatinib, have been approved for treating RET fusion NSCLC due to their remarkable efficacy and safety profiles. These inhibitors have shown the ability to overcome resistance to multikinase inhibitors (MKIs). Furthermore, ongoing clinical trials are investigating several second-generation sRETis that are specifically designed to target solvent front mutations, which pose a challenge for first-generation sRETis. The effective screening of patients is the first crucial step in the clinical application of RET-targeted therapy. Currently, four methods are widely used for detecting gene rearrangements: next-generation sequencing (NGS), reverse transcription-polymerase chain reaction (RT-PCR), fluorescence in situ hybridization (FISH), and immunohistochemistry (IHC). Each of these methods has its advantages and limitations. To streamline the clinical workflow and improve diagnostic and treatment strategies for RET fusion NSCLC, our expert group has reached a consensus. Our objective is to maximize the clinical benefit for patients and promote standardized approaches to RET fusion screening and therapy.

Clinical insights into small cell lung cancer: Tumor heterogeneity, diagnosis, therapy, and future directions

Small cell lung cancer (SCLC) is characterized by rapid growth and high metastatic capacity. It has strong epidemiologic and biologic links to tobacco carcinogens. Although the majority of SCLCs exhibit neuroendocrine features, an important subset of tumors lacks these properties. Genomic profiling of SCLC reveals genetic instability, almost universal inactivation of the tumor suppressor genes TP53 and RB1, and a high mutation burden. Because of early metastasis, only a small fraction of patients are amenable to curative-intent lung resection, and these individuals require adjuvant platinum-etoposide chemotherapy. Therefore, the vast majority of patients are currently being treated with chemoradiation with or without immunotherapy. In patients with disease confined to the chest, standard therapy includes thoracic radiotherapy and concurrent platinum-etoposide chemotherapy. Patients with metastatic (extensive-stage) disease are treated with a combination of platinum-etoposide chemotherapy plus immunotherapy with an anti-programmed death-ligand 1 monoclonal antibody. Although SCLC is initially very responsive to platinum-based chemotherapy, these responses are transient because of the development of drug resistance. In recent years, the authors have witnessed an accelerating pace of biologic insights into the disease, leading to the redefinition of the SCLC classification scheme. This emerging knowledge of SCLC molecular subtypes has the potential to define unique therapeutic vulnerabilities. Synthesizing these new discoveries with the current knowledge of SCLC biology and clinical management may lead to unprecedented advances in SCLC patient care. Here, the authors present an overview of multimodal clinical approaches in SCLC, with a special focus on illuminating how recent advancements in SCLC research could accelerate clinical development.

RET-Altered Cancers-A Tumor-Agnostic Review of Biology, Diagnosis and Targeted Therapy Activity

RET alterations, such as fusions or mutations, drive the growth of multiple tumor types. These alterations are found in canonical (lung and thyroid) and non-canonical (e.g., gastrointestinal, breast, gynecological, genitourinary, histiocytic) cancers. RET alterations are best identified via comprehensive next-generation sequencing, preferably with DNA and RNA interrogation for fusions. Targeted therapies for RET-dependent cancers have evolved from older multikinase inhibitors to selective inhibitors of RET such as selpercatinib and pralsetinib. Prospective basket trials and retrospective reports have demonstrated the activity of these drugs in a wide variety of RET-altered cancers, notably those with RET fusions. This paved the way for the first tumor-agnostic selective RET inhibitor US FDA approval in 2022. Acquired resistance to RET kinase inhibitors can take the form of acquired resistance mutations (e.g., RET G810X) or bypass alterations.

Tumor plasticity and therapeutic resistance in oncogene-addicted non-small cell lung cancer: from preclinical observations to clinical implications

The identification of actionable targets in oncogene-addicted non-small cell lung cancer (NSCLC) has fueled biomarker-directed strategies, especially in advanced stage disease. Despite the undeniable success of molecular targeted therapies, duration of clinical response is relatively short-lived. While extraordinary efforts have defined the complexity of tumor architecture and clonal evolution at the genetic level, not equal interest has been given to the dynamic mechanisms of phenotypic adaptation engaged by cancer during treatment. At the clinical level, molecular targeted therapy of EGFR-mutant and ALK-rearranged tumors often results in epithelial-to-mesenchymal transition (EMT) and histological transformation of the original adenocarcinoma without the acquisition of additional genetic lesions, thus limiting subsequent therapeutic options and patient outcome. Here we provide an overview of the current understanding of the genetic and non-genetic molecular circuits governing this phenomenon, presenting current strategies and potentially innovative therapeutic approaches to interfere with lung cancer cell plasticity.