Small-cell carcinoma in the setting of pulmonary adenocarcinoma: new insights in the era of molecular pathology

Transcriptomic analysis of transformed small-cell lung cancer from EGFR-mutated lung adenocarcinoma reveals distinct subgroups and precision therapy opportunities

BACKGROUND

Small-cell lung cancer (SCLC) transformation is one of the major mechanisms of resistance to Epidermal Growth Factor Receptor tyrosine kinase inhibitors (EGFR-TKIs). Chemotherapy is typically the recommended treatment for transformed SCLC (T-SCLC), similar to primary SCLC. However, the benefits of chemotherapy alone are minimal. Prior research highlights differences between the biological traits of T-SCLC and primary SCLC or EGFR-mutated lung adenocarcinoma (LUAD). This study aims to elucidate the molecular characteristics of T-SCLC and identify potential treatment modalities.

METHODS

We retrospectively collected tissue samples from LUAD, T-SCLC post-EGFR-TKI resistance, and primary SCLC. Genomics, transcriptomics, and proteomics were performed to clarify the differences between T-SCLC, LUAD, and primary SCLC. Hierarchical clustering analysis was then used to categorize the molecular subtype of T-SCLC, followed by a survival analysis based on these subtypes.

RESULTS

A study involving 61 patients investigated differences between LUAD, SCLC, and primary SCLC. RNA sequencing revealed distinct gene expression variations, particularly up-regulation in PPM1E, INSM1, and KCNC1 genes in T-SCLC. Pathway analysis linked T-SCLC to the cell cycle and neural differentiation. By conducting Hierarchical clustering analysis on RNA-seq data, the entire population can be categorized into two distinct groups. While certain T-SCLC showed similarities and differences compared to SCLC, with subtypes: LUAD-like and Non-LUAD-like. Notably, the LUAD-like subtype had significantly higher NKX2-1 expression (mean 371.8 vs. 41.8, P < 0.0001). T-SCLC treatment approaches were categorized into matched and unmatched groups, delineated by the alignment of specific therapies with corresponding pathologies. The matched group (13 cases) exhibited a significantly prolonged median progression-free survival compared to the unmatched group (10 cases) (5.4 months vs. 3.6 months, P = 0.02).

CONCLUSIONS

T-SCLC exhibits marked molecular distinctiveness, setting it apart not only from LUAD but also from classical SCLC. This distinction extends to its classification into two discernible molecular subtypes: LUAD-like and Non-LUAD-like. Customizing therapeutic protocols to align with these specific subtypes have the potential to identify the most appropriate treatment for T-SCLC.

Primary de novo Epidermal Growth Factor Receptor Mutant Small Cell Lung Carcinomas: Clinicopathological Study of a Rare Entity Presenting in Treatment-Naïve Setting with Review of Literature

Introduction: Small cell lung carcinomas (SCLC) are characterized by loss of function mutations in genes encoding for p53 (tumor protein p53-TP53) and retinoblastoma transcriptional corepressor 1 (RB1) proteins in the majority of tumors. They are aggressive, usually present with metastatic disease, and are treated with platinum-based chemotherapy with overall poor outcomes. Epidermal growth factor receptor (EGFR) mutations, classically associated with primary lung adenocarcinomas, have been reported in rare de novo SCLC outside the context of the relatively more common transformed SCLC that arise with emergence of tyrosine kinase inhibitor resistance in EGFR-mutant adenocarcinomas. Aim: To analyze the clinicopathological features of EGFR-mutant de novo SCLC. Methods: EGFR-mutant de novo SCLCs were retrieved over 5 years and reviewed for clinicopathological parameters. Results: Five patients were identified harboring either exon 19 deletion (n = 4) or exon 21 L858R mutation (n = 1) in EGFR. Median age at diagnosis was 48 years (30-58 years). Four patients were never-smokers of whom three were tobacco chewers. Three biopsies showed pure small cell carcinoma while others showed composite adenocarcinoma. Diffuse loss of RB1 (5/5) and mutant type p53 staining pattern (3/3) were noted in all tested samples. Among two patient samples subjected to sequencing, additional pathogenic mutations in TP53 (2/2), RB1 (1/2), PTEN (1/2), neurofibromatosis type 1 (1/2), and CREBB1 (1/2) were identified. Conclusion: EGFR-mutant de novo SCLCs are extremely rare and show frequent inactivation of p53 and RB1, like the more common transformed SCLCs. Given the lack of tyrosine kinase inhibitor exposure, these tumors highlight the inherent lineage plasticity of EGFR/TP53/RB1 triple mutant lung carcinomas.

EGFR-mutant lung adenocarcinoma transformed into small cell Lung cancer: A case report and literatures review

Advances in molecular biology have positioned epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) as highly effective therapies for patients with EGFR-mutant carcinomas. However, the inevitable emergence of acquired resistance significantly limits their long-term efficacy. Among resistance mechanisms, the transformation of lung adenocarcinoma to small cell lung cancer (SCLC) following EGFR-TKIs therapy is an uncommon but clinically important phenomenon contributing to treatment failure. We present a case of SCLC transformation in a patient with EGFR-mutant lung adenocarcinoma after 8 months of first-line osimertinib therapy. Following 4 cycles of etoposide combined with lobaplatin chemotherapy, adenocarcinoma cells regained predominance, illustrating a dynamic histological shift between adenocarcinoma and SCLC phenotypes. Subsequent treatment with 2 cycles of chemotherapy plus osimertinib resulted in disease stabilization. However, multiple brain metastases were identified 3 months after completing 6 cycles of chemotherapy. This case underscores the bidirectional histological plasticity between lung adenocarcinoma and SCLC during treatment and highlights the critical importance of repeated biopsies for guiding management strategies in the context of resistance. We also provide a comprehensive review of the clinical manifestations, underlying mechanisms, predictive biomarkers, and therapeutic approaches for SCLC transformation.

Case Report: Transforming small cell lung cancer: two cases report and literature review

Transformation of non-small cell lung cancer (NSCLC) to small cell lung cancer (SCLC) is a relatively rare event with an incidence of about 3%-14%. Due to the poor treatment outcomes and prognosis associated with this transformation, understanding its underlying mechanisms is crucial for improving the diagnosis, management, and prognosis of transformed small cell lung cancer (T-SCLC). In this paper, we present two cases of T-SCLC and review the molecular mechanisms, clinical features, and treatment strategies post-transformation. We emphasize the importance of considering pathological transformation in cases of resistance to NSCLC treatment, monitoring changes in tumor markers, and conducting a re-biopsy. Finally, we propose effective treatment measures for managing T-SCLC.

Partial transformation from non-small cell lung cancer to small cell lung cancer: a case report and literatures review

A fraction of lung adenocarcinoma patients with gene mutations who receive targeted therapy would experience acquired resistance and undergo small cell lung cancer (SCLC) transformation. The mechanisms behind the transformation of tumor pathological types and the treatment strategies are not fully clear. There have been case reports of the transformation from adenocarcinoma to SCLC, but the partial transformation from adenocarcinoma to SCLC has not been reported. We reported a case of a patient with partial transformation from lung adenocarcinoma to SCLC for the first time. The patient was diagnosed as lung adenocarcinoma with epidermal growth factor receptor (EGFR) 19 exon mutation and Tumor protein p53 (TP53) mutation. She received Epithelial growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) treatment. However, the tumor progression occurred and the lung aspiration pathology revealed a transformation from non-small cell lung cancer (NSCLC) to SCLC. The treatment regimen was changed to cisplatin and etoposide (EP) chemotherapy, resulting in a 2-month PFS. It was worth mentioning that adenocarcinoma cells were found in the patient's emerging pericardial effusion, suggesting the co-existence of both adenocarcinoma and SCLC components. This is the first report of partial transformation from NSCLC to SCLC in the context of definitive pathology. It highlights that when no more pathological biopsy is feasible, we should be alert to the partial transformation and adopt the appropriate treatment.

The emerging landscape and future perspective of SCLC transformation: From molecular mechanisms to therapeutic strategies

Small-cell lung cancer (SCLC) is featured by high malignancy and undesirable prognosis. Transformed SCLC shares several common grounds but differ in biological behavior, molecular mechanism and therapeutic options from typical SCLC. SCLC transformation exerts indispensable role in drug resistance among patients with non-small cell lung cancer (NSCLC) upon various treatment modalities. Two hypotheses have been raised to account for SCLC transformation. It develops mostly in EGFR-mutant adenocarcinoma, and can also occur in ALK or ROS1 mutant patients, and EGFR-wildtype adenocarcinoma. Effective biomarkers for early detection, and therapeutic strategies are vital for improving survival for patients undergoing SCLC transformation. This review summarizes the emerging landscape in transformed SCLC, including its origin, molecular mechanisms, approaches for early detection and corresponding therapeutic options, in a bid to gain a comprehensive insight of this recalcitrant and tricky disease. More importantly, we also discuss challenges that lie ahead and future perspectives on this aggressive malignancy.

Baseline retinoblastoma transcriptional corepressor 1 (Rb1) functional inactivation is a pre-requisite but not sufficient for small-cell histological transformation in epidermal growth factor receptor (EGFR) mutant lung adenocarcinomas post-tyrosine kinase inhibitor therapy

Small-cell transformation is an uncommon mechanism of tyrosine receptor kinase inhibitor (TKI) resistance in epidermal growth factor receptor (EGFR)-mutant lung adenocarcinomas. This study aims to assess the dynamic changes in the molecular landscape and Rb1 functional status in EGFR-mutant lung adenocarcinomas transforming to small-cell carcinomas post-treatment with EGFR-TKIs. This is an ambispective study (2019-2023) wherein the baseline and post-TKI biopsies of EGFR-mutant lung adenocarcinomas with small-cell transformation were subject to Rb1 immunohistochemistry and 72-gene targeted panel next-generation sequencing. Rb1-deficiency was defined as Rb1 protein loss or Rb1retained/p16high/Cyclin-D1low protein expression profile with RB1 mutations. A cohort of EGFR-mutant lung adenocarcinomas without small-cell transformation was included for Rb1 status comparison. Small-cell transformation was diagnosed in 9 patients (10%, 9/84) on their post-TKI biopsy. All their tested baseline adenocarcinoma (n = 7) and post-TKI small-cell carcinoma (n = 9) samples were Rb1-deficient, with additional TP53 (11/11) and PTEN mutations (2/11). Eighteen paired samples from 9 patients without small-cell transformation revealed Rb1-deficiency in one patient (1/9) only. Baseline functional inactivation of Rb1 is nearly universal in EGFR-mutant adenocarcinomas transforming to small-cell carcinomas post-EGFR TKI suggesting that Rb1 loss is prerequisite for small-cell transformation. However, it is likely not sufficient as not all adenocarcinomas with baseline Rb1 loss transform into small-cell carcinomas. Except for TP53 and PTEN, recurrent mutations in other common oncogenes tested were not detected at baseline or at progression. Within the limitation of a small sample size, specific molecular events that drive small-cell transformation remain unclear.

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.

Histological transformation in lung adenocarcinoma: Insights of mechanisms and therapeutic windows

Histological transformation from lung adenocarcinoma (ADC) to small cell lung carcinoma (SCLC), large cell neuroendocrine carcinoma (LCNEC), squamous cell carcinoma (SCC), and sarcomatoid carcinoma (PSC) after targeted therapies is recognized as a mechanism of resistance in ADC treatments. Patients with transformed lung cancer typically experience a poor prognosis and short survival time. However, effective treatment options for these patients are currently lacking. Therefore, understanding the mechanisms underlying histological transformation is crucial for the development of effective therapies. Hypotheses including intratumoral heterogeneity, cancer stem cells, and alteration of suppressor genes have been proposed to explain the mechanism of histological transformation. In this review, we provide a comprehensive overview of the known molecular features and signaling pathways of transformed tumors, and summarized potential therapies based on previous findings.

A Case Report of Concurrent Epidermal Growth Factor Receptor (EGFR) Exon 18 (G719A) and Exon 21 (L833_V834delinsFL) Mutations and Treatment Challenges

Molecular profiling of lung tumors is crucial for guiding targeted therapeutic strategies and identifying potential resistance mechanisms to specific therapies, such as epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs). During this profiling, mutations with uncertain treatment implications can be identified. This case study represents a 69-year-old female with a co-occurring EGFR mutation profile that presents a unique therapeutic challenge. Tumor DNA was used for next-generation sequencing (NGS) of a custom 275 cancer-related QIAseq Human Comprehensive Cancer Panel (Qiagen). Next-generation RNA sequencing was performed using the Illumina TruSight panel. FISH analysis and PD-L1 22C3 immunohistochemical testing were also performed. Microscopic analysis revealed an invasive adenocarcinoma with papillary, acinar, and focal micropapillary features with a 6 mm invasive component. The final pathology stage was determined to be pT1aN0M0. NGS for DNA variant detection identified two mutations in EGFR, an EGFR G719A and EGFR L833_V834delinsFL with a variant allele frequency (VAF) of 22.2% and 21.1%, respectively. Targeted NGS RNA fusion analysis was also performed, which came back negative. PD-L1 22C3 immunohistochemical testing showed only 1% of the tumor cells expression. FISH analysis revealed one copy of MET and D7Z1 in 27% of cells, indicating an aneuploid neoplastic clone with monosomy 7. EGFR TKIs are universally accepted as a first-line treatment for advanced non-small cell lung cancer (NSCLC) patients with a sensitizing EGFR mutation. While mutations such as G719A are sensitive to all generations of EGFR-TKI, the effects are unknown for rare compound mutations in EGFR, such as EGFR L833_V834delinsFL. There are no reports in the literature with any mention of an algorithm of treatment for such a case. The patient had two metachronous lung primary cancers resected in 2022 and 2024. Due to the complete surgical resection, the sensitivity of this mutation of TKIs could not be established. This unique mutation profile still remains of paramount importance to understand if the patient relapses or presents with a new tumor with the same genetic profile.

Transformation of epidermal growth factor receptor mutated lung adenocarcinoma to small-cell carcinoma long after the cessation of tyrosine kinase inhibitor treatment: A case series and literature review

Histological transformation to small-cell lung cancer (SCLC) is a well-known mechanism of acquired resistance to epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs), and almost all patients receive EGFR-TKIs at the time of transformation. We herein report three cases of EGFR-mutated lung adenocarcinoma that transformed into SCLC long after the cessation of EGFR-TKIs. Rapid tumor progression and elevated SCLC marker levels were observed at the time of transformation. Our case highlights the importance of considering SCLC transformation throughout the clinical course. Careful observation of the tumor behavior and SCLC markers should be performed to avoid diagnostic delays.

Comprehensive molecular and clinical insights into non-small cell lung cancer transformation to small cell lung cancer with an illustrative case report

Histologic transformation to small cell lung cancer (tSCLC) is a rare but increasingly recognised mechanism of acquired resistance to tyrosine kinase inhibitors (TKI) in patients with epidermal growth factor receptor (EGFR)-positive non-small cell lung cancer (NSCLC). Beyond its acknowledged role in TKI resistance, histologic transformation to SCLC might be an important, yet under-recognised, mechanism of resistance in NSCLC treated with immunotherapy. Our review identified 32 studies that investigated tSCLC development in patients with EGFR-mutated NSCLC treated with TKI therapy and 16 case reports of patients treated with immunotherapy. It revealed the rarity of tSCLC, with a predominance of EGFR exon 19 mutations and limited therapeutic options and outcomes. Across all analysed studies in EGFR-mutated NSCLC treated with TKI therapy, the median time to tSCLC development was ∼17 months, with a median overall survival of 10 months. Histologic transformation of EGFR-mutated NSCLC to SCLC is a rare, but challenging clinical problem with a poor prognosis. A small number of documented cases of tSCLC after immunotherapy highlight the need for rebiopsies at progression to diagnose this potential resistance mechanism. Further research is needed to better understand the mechanisms underlying this phenomenon and to develop more effective treatment strategies for patients with tSCLC.

Advances in combined neuroendocrine carcinoma of lung cancer

Lung cancer incidence and mortality rates are increasing worldwide, posing a significant public health challenge and an immense burden to affected families. Lung cancer encompasses distinct subtypes, namely, non-small-cell lung cancer (NSCLC) and small-cell lung cancer (SCLC). In clinical investigations, researchers have observed that neuroendocrine tumors can be classified into four types: typical carcinoid, atypical carcinoid, small-cell carcinoma, and large-cell neuroendocrine carcinoma based on their unique features. However, there exist combined forms of neuroendocrine cancer. This study focuses specifically on combined pulmonary carcinomas with a neuroendocrine component. In this comprehensive review article, the authors provide an overview of combined lung cancers and present two pathological images to visually depict these distinctive subtypes.

Small cell lung cancer transformations from non-small cell lung cancer: Biological mechanism and clinical relevance

Lung cancer is a leading cause of cancer deaths worldwide, consisting of two major histological subtypes: small-cell lung cancer (SCLC) and non-small-cell lung cancer (NSCLC). In some cases, NSCLC patients may undergo a histological transformation to SCLC during clinical treatments, which is associated with resistance to targeted therapy, immunotherapy, or chemotherapy. The review provides a comprehensive analysis of SCLC transformation from NSCLC, including biological mechanism, clinical relevance, and potential treatment options after transformation, which may give a better understanding of SCLC transformation and provide support for further research to define better therapy options.

Small cells - big issues: biological implications and preclinical advancements in small cell lung cancer

Current treatment guidelines refer to small cell lung cancer (SCLC), one of the deadliest human malignancies, as a homogeneous disease. Accordingly, SCLC therapy comprises chemoradiation with or without immunotherapy. Meanwhile, recent studies have made significant advances in subclassifying SCLC based on the elevated expression of the transcription factors ASCL1, NEUROD1, and POU2F3, as well as on certain inflammatory characteristics. The role of the transcription regulator YAP1 in defining a unique SCLC subset remains to be established. Although preclinical analyses have described numerous subtype-specific characteristics and vulnerabilities, the so far non-existing clinical subtype distinction may be a contributor to negative clinical trial outcomes. This comprehensive review aims to provide a framework for the development of novel personalized therapeutic approaches by compiling the most recent discoveries achieved by preclinical SCLC research. We highlight the challenges faced due to limited access to patient material as well as the advances accomplished by implementing state-of-the-art models and methodologies.

Correlation Analysis between T790M Status and Clinical Characteristics of Patients with EGFR-sensitive Mutation Advanced NSCLC who Progressed after the First Generation and First-line EGFR-TKIs Administration: A Real-world Exploratory Study

AIM

The present study is to investigate the association between T790M status and clinical characteristics of patients with EGFR-sensitive advanced non-small cell lung cancer (NSCLC) who progressed the initial epidermal growth factor receptor tyrosine kinase inhibitors (EGFRTKIs) administration.

METHODS

A total of 167 patients with EGFR-sensitive mutations advanced NSCLC who had successful genetic tests and progressed the initial EGFR-TKI treatment were included in this study retrospectively. The clinical and demographic characteristics of these patients were collected, which were manifested as pathological type, metastasis location, initial biopsy method, initial genetic test specimens, and baseline gene mutations status. Correlation analysis between T790M status and these characteristics was performed and prognostic analysis regarding the different subgroups was carried out accordingly.

RESULTS

The prevalence of secondary T790M after resistance to initial EGFR-TKIs among the 167 patients was 52.7%. Correlation analysis indicated that the median progression-free Survival (PFS) to initial EGFR-TKIs >12 months were more likely to develop secondary T790M in univariate analysis. However, the conclusion failed to show statistically significant in multivariate analysis. Additionally, patients with intracranial progression of initial EGFR-TKIs therapy were associated with secondary EGFR-T790M. However, it should be noted that those whose best overall response was partial response (PR) during the EGFR-TKI therapy were relevant to secondary T790M. Furthermore, The median PFS of the initial EGFR-TKIs administration was longer among patients with T790M positive mutation and patients with PR reaction than those without T790M mutation and patients with stable disease (SD), respectively (median PFS: 13.6 vs. 10.9 months, P=0.023) and (median PFS: 14.0 vs. 10.1 months, P=0.001).

CONCLUSION

This retrospective study highlighted the real-world evidence that the best efficacy and intracranial progression with initial EGFR-TKIs therapy among patients with advanced NSCLC might be the promising indicators to predict the occurrence of EGFR-T790M. Patients with PR reaction and T790M positive mutation conferred longer PFS of the initial EGFR-TKIs administration. Also, the conclusion should be confirmed in more patients with advanced NSCLC subsequently.

Current Knowledge of Small Cell Lung Cancer Transformation from Non-Small Cell Lung Cancer

Lung cancer is the leading cause of cancer related death, and is divided into two major histological subtypes, non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). Histological transformation from NSCLC to SCLC has been reported as a mechanism of treatment resistance in patients who received tyrosine kinase inhibitors (TKIs) targeting EGFR, ALK and ROS1 or immunotherapies. The transformed histology could be due to therapy-induced lineage plasticity or clonal selection of pre-existing SCLC cells. Evidence supporting either mechanism exist in the literature. Here, we discuss potential mechanisms of transformation and review the current knowledge about cell of origin of NSCLC and SCLC. In addition, we summarize genomic alterations that are frequently observed in both "De novo" and transformed SCLC, such as TP53, RB1 and PIK3CA. We also discuss treatment options for transformed SCLC, including chemotherapy, radiotherapy, TKIs, immunotherapy and anti-angiogenic agents.

Challenges of EGFR-TKIs in NSCLC and the potential role of herbs and active compounds: From mechanism to clinical practice

Epidermal growth factor receptor (EGFR) mutations are the most common oncogenic driver in non-small cell lung cancer (NSCLC). Epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) are widely used in the treatment of lung cancer, especially in the first-line treatment of advanced NSCLC, and EGFR-TKIs monotherapy has achieved better efficacy and tolerability compared with standard chemotherapy. However, acquired resistance to EGFR-TKIs and associated adverse events pose a significant obstacle to targeted lung cancer therapy. Therefore, there is an urgent need to seek effective interventions to overcome these limitations. Natural medicines have shown potential therapeutic advantages in reversing acquired resistance to EGFR-TKIs and reducing adverse events, bringing new options and directions for EGFR-TKIs combination therapy. In this paper, we systematically demonstrated the resistance mechanism of EGFR-TKIs, the clinical strategy of each generation of EGFR-TKIs in the synergistic treatment of NSCLC, the treatment-related adverse events of EGFR-TKIs, and the potential role of traditional Chinese medicine in overcoming the resistance and adverse reactions of EGFR-TKIs. Herbs and active compounds have the potential to act synergistically through multiple pathways and multiple mechanisms of overall regulation, combined with targeted therapy, and are expected to be an innovative model for NSCLC treatment.

Small Cell Lung Cancer in Light/Never Smokers - A Role for Molecular Testing?

This report describes the management of small cell lung cancer (SCLC) transformation in a patient with untreated ALK-mutated advanced disease and a minimal smoking history, and a separate case of a de novo SCLC in a lifelong nonsmoker found to have a potentially targetable ERBB2 alteration. In the first case, chemotherapy followed by a targeted inhibitor was chosen due to the presence of the ALK rearrangement, as well as a somewhat discordant response to induction chemotherapy, suggesting possible progression of the ALK inhibitor-sensitive component. Molecular testing for the identification of driver mutations should be considered in patients with SCLC who have light/never smoking histories in order to help understand the incidence and ultimate optimal management strategies.

Progress in the knowledge on the transformation of lung adenocarcinoma to small-cell lung cancer

Lung cancer is a common type of carcinoma and is the leading cause of cancer-related deaths worldwide. The two broad histological subtypes of lung cancer are non-small-cell lung cancer (NSCLC), which accounts for 85% of cases and includes adenocarcinoma and squamous cell carcinoma, and small-cell lung cancer (SCLC), which accounts for 15% of cases. Substantial improvements in treatment have led to remarkable progress and changed outcomes for many patients in the past two decades. However, with prolonged survival time and awareness of repeat biopsy, more and more patients with lung cancer have been found to undergo a histological transformation during treatment, with lung adenocarcinoma (LAdC) to SCLC transformation being the most frequent. In this article, we summarized findings on the mechanism, clinical characteristics, therapeutic strategies, and predictors of the transformation of LAdC to SCLC. A non-systematic narrative review was performed using the Pubmed/MEDLINE (US National Library of Medicine National Institutes of Health) database with the following keywords: "transformation from NSCLC to SCLC," "transformation from lung adenocarcinoma to small-cell lung cancer," "NSCLC transformation in SCLC," and "NSCLC and transformation and SCLC." Articles published until June 2022 were analyzed. Search results were limited to human studies without restriction for language.

Emerging strategies to overcome resistance to third-generation EGFR inhibitors

Epidermal growth factor receptor (EGFR), the receptor for members of the epidermal growth factor family, regulates cell proliferation and signal transduction; moreover, EGFR is related to the inhibition of tumor cell proliferation, angiogenesis, invasion, metastasis, and apoptosis. Therefore, EGFR has become an important target for the treatment of cancer, including non-small cell lung cancer, head and neck cancer, breast cancer, glioma, cervical cancer, and bladder cancer. First- to third-generation EGFR inhibitors have shown considerable efficacy and have significantly improved disease prognosis. However, most patients develop drug resistance after treatment. The challenge of overcoming intrinsic and acquired resistance in primary and recurrent cancer mediated by EGFR mutations is thus driving the search for alternative strategies in the design of new therapeutic agents. In view of resistance to third-generation inhibitors, understanding the intricate mechanisms of resistance will offer insight for the development of more advanced targeted therapies. In this review, we discuss the molecular mechanisms of resistance to third-generation EGFR inhibitors and review recent strategies for overcoming resistance, new challenges, and future development directions.

Comprehensive genetic analysis of histological components of combined small cell carcinoma

Background

Combined small‐cell lung cancer (cSCLC) is a rare type of small‐cell lung cancer (SCLC) that includes both SCLC and non‐small‐cell lung cancer (NSCLC). The molecular biological mechanisms underlying the heterogeneity of histological types in combined or metachronously transformed SCLC (mtSCLC) remain unclear. This study aimed to investigate the relationship between genetic alterations and each histological component heterogeneously detected in cSCLC and mtSCLC.

Methods

This study included four cSCLC cases and one mtSCLC case. Formalin‐fixed and paraffin‐embedded sections of each histological component of these tumors were subjected to next‐generation sequencing (NGS) and quantitative reverse transcription‐polymerase chain reaction to investigate the genetic mutations and expression levels of neuroendocrine cell‐specific transcription factors (achaete‐scute homolog‐1 [ASCL1], brain‐2 [BRN2] also known as POU domain class 3 transcription factor 2, nuclear factor 1 B [NF1B], insulinoma‐associated protein 1 [INSM1], and thyroid transcription factor‐1 [TTF‐1]).

Results

NGS analysis revealed that SCLC and NSCLC components share the same somatic mutations detected most frequently in TP53, and also in RB1 and EGFR. Gene expression analysis showed ASCL1 expression was significantly lower in the NSCLC component than in the SCLC component.

Conclusion

We conclude that the morphological evolution of heterogeneous histological components in cSCLC may be associated with differences in ASCL1 expression levels, but not in acquired somatic gene mutations.

Transformation from lung adenocarcinoma to combined small cell carcinoma in pleural effusion after treatment with osimertinib

The transformation of lung adenocarcinoma to combined small cell lung cancer is a rare mechanism of acquired resistance to EGFR tyrosine kinase inhibitors. This case describes this mechanism in a pleural effusion of a young patient treated with osimertinib for 18 months.

Morphologic-Molecular Transformation of Oncogene Addicted Non-Small Cell Lung Cancer

Patients with non-small cell lung cancer, especially adenocarcinomas, harbour at least one oncogenic driver mutation that can potentially be a target for therapy. Treatments of these oncogene-addicted tumours, such as the use of tyrosine kinase inhibitors (TKIs) of mutated epidermal growth factor receptor, have dramatically improved the outcome of patients. However, some patients may acquire resistance to treatment early on after starting a targeted therapy. Transformations to other histotypes-small cell lung carcinoma, large cell neuroendocrine carcinoma, squamous cell carcinoma, and sarcomatoid carcinoma-have been increasingly recognised as important mechanisms of resistance and are increasingly becoming a topic of interest for all specialists involved in the diagnosis, management, and care of these patients. This article, after examining the most used TKI agents and their main biological activities, discusses histological and molecular transformations with an up-to-date review of all previous cases published in the field. Liquid biopsy and future research directions are also briefly discussed to offer the reader a complete and up-to-date overview of the topic.

Small cell lung cancer transformation: From pathogenesis to treatment

Small cell lung cancer (SCLC) is a type of neuroendocrine tumor with high malignancy and poor prognosis. Besides the de novo SCLC, there is transformed SCLC, which has similar characteristics of pathological morphology, molecular characteristics, clinical manifestations and drug sensitivity. However, de novo SCLC and transformed SCLC have different pathogenesis and tumor microenvironment. SCLC transformation is one of the mechanisms of resistance to chemotherapy, immunotherapy, and targeted therapy in NSCLC. Two hypotheses have been used to explain the pathogenesis of SCLC transformation. Although SCLC transformation is not common in clinical practice, it has been repeatedly identified in many small patient series and case reports. It usually occurs in epidermal growth factor receptor (EGFR) mutant lung adenocarcinoma after treatment with tyrosine kinase inhibitors (TKIs). SCLC transformation can also occur in anaplastic lymphoma kinase (ALK)-positive lung cancer after treatment with ALK inhibitors and in wild-type EGFR or ALK NSCLC treated with immunotherapy. Chemotherapy was previously used to treat transformed SCLC, yet it is associated with an unsatisfactory prognosis. We comprehensively review the advancements in transformed SCLC, including clinical and pathological characteristics, and the potential effective treatment after SCLC transformation, aiming to give a better understanding of transformed SCLC and provide support for clinical uses.

Outcomes in Patients With Lung Adenocarcinoma With Transformation to Small Cell Lung Cancer After EGFR Tyrosine Kinase Inhibitors Resistance: A Systematic Review and Pooled Analysis

Background

Lung adenocarcinoma can transform into small-cell lung cancer (SCLC) when resistance to tyrosine kinase inhibitors (TKIs) develops. Approximately 3% to 10% of epidermal growth factor receptor (EGFR)-mutant non-small cell lung cancer (NSCLC) could transform to SCLC. This phenomenon has been described in several case reports and small patient series. However, the characteristics and treatment outcomes of this population have not been comprehensively reported, and their clinical course is poorly characterized.

Methods

We performed a systematic review of the published literature to summarize the clinical and pathological features and prognosis of the reported cases and analyzed the demographics, disease features, and outcomes.

Results

A total of 72 patients (50 females and 22 males) initially diagnosed with lung adenocarcinoma were included. EGFR mutations included 19-deletion (75%), L858R (22%), and G719X (3%). All patients received EGFR-TKIs before SCLC transformation. The median time from diagnosis to transformation was 20.5 months (95% CI, 15.45 to 26.55 months). Of the 67 patients with post-translational gene test results, 58 maintained their EGFR mutation, and only 1 of 18 with prior T790M positivity retained T790M mutation. After the pathological transformation, both conventional chemotherapy regimen and chemotherapy combined targeted therapy yielded high response rates. The disease control rate of first-line therapy after transformation was 76%, while the objective response rate was 48%. The median overall survival (OS) since diagnosis was 27 months (95% CI, 22.90 to 31.10 months), whereas median OS since SCLC transformation was 8.5 months (95% CI, 5.50 to 11.60 months).

Conclusion

The prognosis of transformed SCLC is worse than primary SCLC. The response rate to conventional chemotherapy was high. However, the progression-free survival and OS after transformation were short and the prognosis was poor with first-line therapies. New therapies are needed in the management of transformed SCLC.

Characterization of non-small cell lung cancer transforming to small cell lung cancer and its response to EGFR-TKI: a case report

Epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) have demonstrated significant survival benefits for advanced non-small cell lung cancer (NSCLC) patients with sensitive EGFR mutations. However, patients with EGFR-TKI treatment often develop acquired resistance subsequently. Transformation from NSCLC to small cell lung cancer (SCLC) is a rare EGFR-TKI resistance mechanism for patients with sensitive EGFR mutations. Herein, we report a NSCLC patient with EGFR exon 19 deletion treated with EGFR-TKI. During treatment, the pathological type of tumor showed transformation from NSCLC to combined SCLC and then to pure SCLC after acquiring EGFR-TKI resistance. Genomic analysis revealed that the EGFR exon 19 deletion, TP53 Y220H mutation, and retinoblastomal transcriptional corepressor 1 (RB1) F755V mutation existed persistently. Immunohistochemical results showed the loss of EGFR and RB1 expression in SCLC. The patient received multi-line chemotherapy with platinum agents and experienced a briefly effective window, but died of aggressive tumor progression. We profiled the transformation from NSCLC to SCLC of this case and pointed out the importance of repeat biopsy in response to EGFR-TKI resistance. Our results showed a novel RB1 F755V mutation which may be associated with RB1 loss. This report summarized the clinical characteristics, mechanisms, and predictors of SCLC transformation, and discussed the treatment after transformation.

[MDT Treatment of Small Cell Lung Cancer Complicated with Adenocarcinoma: A Case Report and Literature Review]

Small cell lung cancer (SCLC) is the most malignant lung cancer with the highest mortality. At present, the first-line standard treatment is still based on Etoposide and Platinum chemotherapy. However, for SCLC that progresses after first-line therapy, the treatment options are still very limited. Since the molecular mechanism of first-line drug resistance of SCLC is still unclear, and the precision medicine strategy after first-line drug resistance is still in the pre-clinical stage. The proportion of secondary biopsy and genetic testing is very low after the progress of first-line treatment of SCLC. In this study, we report a case of a middle-aged woman who was first diagnosed with SCLC. Adenocarcinoma with sensitive gene mutations and repeated changes of small cell carcinoma were detected by multiple biopsies during the course of the disease, suggesting that the patient may be a special subtype of SCLC - mixed SCLC (M-SCLC). In this case, the patient has been treated with radiotherapy and chemotherapy, immunotherapy and targeted therapy successively, and the survival time has reached 2 years and 8 months. Through the case report and literature review retrospectively, this study aimed to explore the part patients may start to present hybrid histopathologic types or tissue type change after treatment of SCLC. Biopsy pathologic histology and genetic testing is necessary after disease progression to look for potential therapeutic targets, so as to give precise treatment based on molecular markers detection results and provide the patient with the benefit of survival for as long as possible.
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Histologic Changes in Non-Small Cell Lung Cancer Under Various Treatments: A Comparison of Histology and Mutation Status in Serial Samples

Purpose

Histologic change is a resistant mechanism in lung cancer. The most common histological change is the switch from adenocarcinoma (AdenoCa) to small cell carcinoma (SCC) against to tyrosine kinase inhibitors (TKI). However, it is not clear whether other treatment modalities are involved in the histologic changes.

Materials and Methods

We investigated histological changes in eight cases after various treatments, and compared the molecular profiles between primary tumors and changed tumors using exome sequencing where tissue was available.

Results

Three cases of AdenoCa that were changed into SCC retained the initial mutations after TKI and/or surgical treatment. After treatment with TKI and immunotherapy, an EGFR (epidermal growth factor receptor)-mutant AdenoCa changed to squamous cell carcinoma (SqCa). SqCa in a patient treated with surgery was changed into combined AdenoCa and SqCa. These two cases showed the same genetic variations between the two distinct non–small cell carcinomas (NSCC). Three patients experienced two histologic changes, which the changed tumors returned to its original subtype or changed to a combined tumor after treatments. Four cases showed combined histology in the first or second change.

Conclusion

The histology of NSCC can be changed to a single pattern or combined subtypes after various treatment modalities, and the phenotypic changes seem not fixed. Therefore, additional morphologic changes may occur regardless of their genetic status and types of treatments. To refine the new treatment strategy, consecutive repeated biopsies in progressive disease or recurrent tumor are necessary.

Small cell lung cancer transformation during antitumor therapies: A systematic review

Lung cancer is the most common cause of cancer-related death. Non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) are the two major histological categories of lung cancers. Drug resistance is a great challenge for cancer treatment, and histological transformation from NSCLC to SCLC is one of the mechanisms underlying drug resistance in NSCLC patients. SCLC-transformed patients show combined characteristics of NSCLC and SCLC; however, they lack timely diagnoses and effective treatment strategies. Thus, we reviewed the clinical characteristics of SCLC transformation patients with a literature search to enhance clinical consciousness, diagnosis, and personalized treatment for patients with it.

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.

Small-cell lung cancer transformation from EGFR-mutant adenocarcinoma after EGFR-TKIs resistance: A case report

RATIONALE

With the recent advancements in molecular biology research, epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) have emerged as excellent therapies for patients with EGFR-mutant cancers. However, these patients inevitably develop cross-acquired resistance to EGFR-TKIs. Transformation to small-cell lung cancer (SCLC) is considered a rare resistance mechanism against EGFR-TKI therapy. Here, we report a case of TKI resistance due to SCLC transformation and demonstrate its mechanisms and clinical features.

PATIENT CONCERNS

A 54-year-old Chinese man with a history of smoking for 40 years complained of an intermittent cough in March 2019.

DIAGNOSIS

Transbronchial lung biopsy was performed on the basal segment of the left lower lobe, which confirmed lung adenocarcinoma. In January 2020, repeat biopsy was performed, and the results of immunohistochemistry (IHC) staining showed TTF-1 (+), CK7 (+), napsin A (+), syn (+), and CD56 (+), with a Ki-67 (+) index 80% of small cell carcinomas. Infiltrating adenocarcinomas and small cell carcinomas were observed.

INTERVENTIONS

Icotinib (125 mg thrice daily) was administered as a first-line treatment from June 2019. We subsequently administered a chemotherapy regimen consisting of etoposide (180 mg, days 1-3) plus cisplatin (45 mg, days 1-3) every 3 weeks for 1 cycle after recurrence. As the patient could not tolerate further chemotherapy, he continued taking icotinib orally and received whole-brain radiotherapy 10 times to a total dose of 30 Gy after brain metastases.

OUTCOMES

The patient relapsed after successful treatment with icotinib for 9 months. A partial response was achieved after 4 cycles of chemotherapy, and despite the brief success of chemotherapy, our patient exhibited brain metastasis and metastases of the eleventh thoracic spine and the second lumbar vertebra with pathological fracture. The patient eventually died of aggressive cancer progression.

LESSONS

Our case highlights the possibility of SCLC transformation from EGFR-mutant adenocarcinoma and the importance of repeat biopsy for drug resistance. Serum neuron-specific enolase levels may also be useful for detecting early SCLC transformation.

Case Report: Transformation From Non-Small Cell Lung Cancer to Small Cell Lung Cancer During Anti-PD-1 Therapy: A Report of Two Cases

BACKGROUND

Histological transformation of lung cancer to small cell lung cancer (SCLC) is uncommon. It is a small subset of the possible resistance mechanisms, even in epidermal growth factor receptor (EGFR)-mutated non-small cell lung cancer treated with EGFR-tyrosine kinase inhibitors. Reports on programmed cell death-1 (PD-1) inhibitors are rare. We report two cases of lung squamous carcinomas that transformed to SCLC during anti-PD-1 therapy, and present a detailed description of histological examination of the pre-and post-transformation tissues, hitherto absent from reports on the topic.

CASE PRESENTATION

Case 1: A 69-year-old man was diagnosed with stage IVa squamous cell carcinoma of the lung. He had a programmed cell death-ligand 1 tumor proportion score ≥50%. He achieved partial response after four cycles of sintilimab as first-line treatment. However, sintilimab was discontinued because of severe decrease in hemoglobin levels and platelet counts. Moreover, the occurrence of pleural effusion favored disease progression. Interestingly, bone marrow puncture and biopsy showed transformation to SCLC. Case 2: A 71-year-old man diagnosed with stage IIIa lung squamous cell carcinoma received neoadjuvant chemotherapy, underwent radical surgery, and finally received adjuvant chemotherapy. Five months later, he presented with tumor recurrence. He was treated with nivolumab, though disease progression was observed after four cycles. Notably, a subsequent computed tomography-guided biopsy showed SCLC.

CONCLUSION

Phenotypic transformation to SCLC is a potential mechanism of resistance to immunotherapy in squamous cell carcinomas of the lung. Disease progression should prompt re-biopsy to diagnose potential histological changes to assess the requirement for change in treatment.

Small Cell Lung Cancer Transformation as a Resistance Mechanism to Osimertinib in Epidermal Growth Factor Receptor-Mutated Lung Adenocarcinoma: Case Report and Literature Review

Introduction: Small cell lung cancer (SCLC) transformation represents a mechanism of resistance to osimertinib in EGFR-mutated lung adenocarcinoma, which dramatically impacts patients' prognosis due to high refractoriness to conventional treatments. Case Description: We present the case of a patient who developed a SCLC phenotypic transformation as resistance mechanism to second-line osimertinib for T790M-positive EGFR-mutated NSCLC. Our patient received platinum-etoposide doublet following SCLC switch and achieved a modest clinical benefit which lasted 4 months. NGS and IHC analyses for p53 and Rb were performed on subsequent liver biopsies, revealing baseline TP53 mutation and complete absence of p53 and Rb expression. Primary cell cultures were established following a liver biopsy at the time of SCLC transformation, and drug sensitivity assays showed meaningful cell growth inhibition when osimertinib was added to platinum-etoposide compared with control (p < 0.05). A review of the current literature regarding SCLC transformation after failure of osimertinib was performed. Conclusions: Based on retrospective data available to date, platinum-etoposide chemotherapy is the preferred treatment choice in the occurrence of SCLC transformation after osimertinib failure. The extension of osimertinib in combination with chemotherapy in the occurrence of SCLC transformation as resistance mechanism to osimertinib is a matter of debate. The combination of osimertinib and platinum-etoposide was effective in inhibiting cell growth in our primary cell cultures. Clinical studies are needed to further explore this combination in the occurrence of SCLC transformation as a resistance mechanism to osimertinib.

Extensive-Stage Small Cell Carcinoma Transformation From EGFR Del19-Mutant Lung Adenocarcinoma on Gefitinib at the Twelfth-Year Follow-Up Case Report

INTRODUCTION

The acquired resistance mechanisms in patients with epidermal growth factor receptor (EGFR)-mutant lung cancer, particularly adenocarcinoma (ADC), following treatment with an EGFR tyrosine kinase inhibitor (TKI) have received extensive investigations. The phenotypic transformation to small cell carcinoma (SCCT) has been estimated to occur in approximately 3 to 10% of patients treated with an EGFR-TKI. The prognosis after SCCT is extremely poor.

CASE STUDY

We report about SCCT that occurred 45 months after the initial diagnosis of ADC in an East Asian never-smoker woman with advanced-stage EGFR Del-19-mutant lung ADC treated with combined chemoradiotherapy before the era of insurance coverage for EGFR-TKIs in this country and subsequently gefitinib; deletion at codon 746-750 in exon 19 of the EGFR gene was ascertained in the original formalin-fixed paraffin-embedded lung biopsy tissue. Spinal cord compression at thoracic-12 level from SCCT was successfully relieved with neurosurgical treatment, chemotherapy with etoposide and cisplatin, and radiotherapy, while gefitinib treatment was maintained. Eleven months later, SCCT relapsed in the lung parenchyma, which was resected and was found to be sensitive to second-line weekly topotecan. Prophylactic cranial irradiation was subsequently administered. SCCT was confirmed by MALDI-TOF MS analysis of formalin-fixed paraffin-embedded tissues demonstrating the same exon 19 deletion. At the 12th-year follow-up, the patient remains relapse free with very good performance status. The novelty of this case is the successful interdisciplinary team effort to correct the spinal cord compression by maintaining the patient in an ambulatory state, non-stop use of gefitinib justified by the presence of activating EGFR mutation in SCCT tumor cells, and aggressive dose-intensive chemotherapy and radiotherapy for the SCCT that leads to an unprecedented prolonged remission and survival. This case also supports the observation that SCCT is chemotherapy sensitive, and thus, re-biopsy or complete tumor excision is recommended to understand the mutation profiles of the current tumor. Aggressive prudent administration of systemic chemotherapy obtaining optimal dose intensity leads to the successful management of the patient.

Whole exome sequencing (WES) analysis of transformed small cell lung cancer (SCLC) from lung adenocarcinoma (LUAD)

Background

Histologic transformation of non-small cell lung cancer (NSCLC) to small cell lung cancer (SCLC) is a rare mechanism of acquired resistance to epidermal growth factor receptor (EGFR)-targeted tyrosine kinase inhibitors. However, the SCLC transformation has also been observed in non-

EGFR

mutant NSCLC. In these cases, whether SCLC initially co-exists with NSCLC or originates from initial NSCLC remains to be determined.

Methods

Whole exome sequencing was performed on 10 samples from 5 patients with SCLC transformation from lung adenocarcinoma (LUAD), a main subtype of NSCLC. Somatic mutations and copy number variations (CNVs) were analyzed to explore the differences between initial LUAD and transformed SCLC, as well as the origin of transformed SCLC.

Results

After SCLC transformation, the mutation spectrum changed, with decreased C>T and increased C>A. Compared with initial LUAD, the CNV burden of transformed SCLC was greatly increased (39.0 vs. 61.1, Wilcoxon P=0.4). The higher the CNV burden of LUAD, the shorter the time to SCLC transformation was observed to be; and the higher the CNV burden of transformed SCLC, the shorter the overall survival (OS) after transformation. Clonal evolution analysis showed different clonal components between initial LUAD and transformed SCLC.

Conclusions

The transformation of LUAD into SCLC may be promoted by CNV events rather than mutational events. CNV burden was associated with the time to SCLC transformation and with the OS of patients following SCLC transformation. Transformed SCLC did not evolve directly from the initial LUAD but branched off from LUAD before the time of initial diagnosis.

Combined small cell lung carcinoma harboring ALK rearrangement: A case report and literature review

Combined small cell lung cancer (c‐SCLC) is a relatively rare subtype of SCLC and is defined by the combination of SCLC and any elements of non‐small cell carcinoma (NSCLC). Standard chemotherapy for patients with c‐SCLC has not yet been established. Gene mutations such as epidermal growth factor receptor (EGFR) mutations may be detected in patients with c‐SCLC. However, little is known about anaplastic lymphoma kinase (ALK) rearrangement in c‐SCLC patients. Here, we report a young female patient who was successfully treated with alectinib for ALK‐positive c‐SCLC after failure of immunochemotherapy for SCLC and cytotoxic chemotherapy for adenocarcinoma. Moreover, we performed a literature review of EGFR‐ or ALK‐positive c‐SCLC patients. Our report suggests that ALK testing may be justified in patients with SCLC that contain an adenocarcinoma component.

Key points

Significant findings of the study

• This is the first report describing the treatment course comprising immunochemotherapy and ALK‐TKI in a patient with c‐SCLC harboring ALK rearrangement.

What this study adds

• Our case and literature review suggest that although ALK mutation is rare in patients with c‐SCLC, its identification and treatment with ALK‐TKIs may contribute to clinical benefits.

Transformational Changes Between Non-Small Cell and Small Cell Lung Cancer-Biological and Clinical Relevance-A Review

During the course of therapy, patients with small cell lung cancer have been noted to develop transformation to non-small cell lung cancer and conversely, patients with non-small cell lung cancer have had transformation to small cell lung cancer or other non-small cell histologies. Transformation may occur after prior tyrosine kinase inhibitors, chemotherapy, immunotherapy or radiation therapy. These changes reflect on the overlapping biology of these cell types and the clinical need for re-biopsy at times of disease progression. The optimum therapy after transformation will depend upon prior therapies received, the functional capacity of the patient, and further research to define the best therapy options.

Squamous Cell Transformation of Primary Lung Adenocarcinoma in a Patient With EML4-ALK Fusion Variant 5 Refractory to ALK Inhibitors

Histologic transformation from adenocarcinoma to squamous cell carcinoma in lung cancer has not been reported as a mechanism of resistance to ALK inhibition. This report describes the clinical course of a female former light smoker with metastatic lung adenocarcinoma whose tumor underwent histologic transformation from a well-differentiated lung adenocarcinoma to a well-differentiated lung squamous cell carcinoma in the same location at the left mainstem bronchus while maintaining the ALK fusion oncogene without any resistance mutations. After experiencing disease progression while on crizotinib, the patient participated in clinical trials that provided early access to the novel ALK inhibitors ceritinib and alectinib before they were commercially available. Tumor recurrence occurred at the primary and metastatic central nervous system sites (ie, brain and spine). At tumor progression, liquid biopsy and tumor genomic profiling of plasma cell-free DNA next-generation sequencing (NGS) provided an accurate diagnosis with a short turnaround time compared with the tissue-based targeted capture NGS. The patient received several courses of radiation primarily to the brain and spine during her disease course. Her disease did not respond to the immune checkpoint inhibitor nivolumab, and she died on home hospice approximately 4 years after diagnosis. This case supports the importance of both histopathologic assessment and comprehensive genomic profiling in selecting appropriate treatment for patients with refractory, metastatic, ALK oncogene-driven non-small cell lung cancer. Use of symptom-directed radiation in tandem with ALK inhibitors contributed to the disease and symptomatic control and prolonged survival in this patient.

Pulmonary pleomorphic carcinoma with pembrolizumab monotherapy

Adenocarcinoma (ADC) is the most common form of lung cancer; however, some other types of lung cancer can sometimes mimic ADC. It then takes experienced pathologists and special stains to make the correct diagnosis. Here, we present a patient with pulmonary pleomorphic carcinoma who was misdiagnosed with ADC, and was treated with pembrolizumab for 13 months. The diagnosis and treatment (including immunotherapy) are also reviewed.

Combined Small and Squamous Transformation in EGFR-mutated Lung Adenocarcinoma

Histologic transformation has been described as an acquired mechanism of resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs). We herein report the case of a woman with stage IV lung adenocarcinoma harboring EGFR exon 19 deletions who was initially treated with EGFR-TKIs; several cytotoxic chemotherapeutic regimens were used when resistance developed. A lymph node re-biopsy revealed histologic transformation of the tumor to combined small-cell lung cancer and squamous cell carcinoma with retained EGFR exon 19 deletions. Following sequential chemotherapy appropriate for transformed histology, a clinical response was achieved.

Dynamic changes of acquired T790M mutation and small cell lung cancer transformation in a patient with EGFR-mutant adenocarcinoma after first- and third-generation EGFR-TKIs: a case report

Epithelial growth factor receptor (EGFR) T790M mutation and small cell lung cancer (SCLC) transformation are well-known resistance mechanisms acquired during treatment with EGFR tyrosine kinase inhibitors (TKIs). Various mechanisms sometimes coexist in patients. Here, we report a 57-year-old female diagnosed with stage IV lung adenocarcinoma, who harbored an EGFR exon 19 deletion mutation. This patient initially received gefitinib and progressed after 14 months. A repeat biopsy was performed, and the original EGFR exon 19 deletion and acquired exon 20 T790M mutation were identified. Then, pemetrexed plus carboplatin was administered as second-line and osimertinib as third-line treatment. Rapid progression and mixed response were observed after 2 months on osimertinib, with stable disease of the primary lung lesion but rapid growth of a right lower chest mass. The progressive chest lesion underwent biopsy, and the SCLC transformation was revealed. Furthermore, the patient was treated with etoposide and cisplatin, and she achieved disease control for 4 months. A fourth biopsy both for the primary lung lesion and the chest mass were finally conducted. Interestingly, the histopathology of the two different lesions showed adenocarcinoma and SCLC, respectively. The patient then rapidly suffered brain metastasis, and no EGFR mutations were detected in her cerebrospinal fluid (CSF). Overall survival (OS) of the patient was 29 months. This patient experienced concomitant resistance mechanisms of T790M mutation and SCLC transformation, which might have resulted from intra-tumor heterogeneity and drug-induced selection. Ultimately, this case reminds us that repeat biopsies are essential for patients receiving EGFR-TKIs in order to make appropriate treatment decisions according to the diverse mechanisms of acquired resistance.

Transformation from EGFR/PTEN co-mutated lung adenocarcinoma to small cell carcinoma in lymph node metastasis

There is minimal evidence of EGFR-mutated lung adenocarcinoma transforming to small cell lung carcinoma (SCLC) without the administration of EGFR-tyrosine kinase inhibitor (TKI). Here, we present a case of EGFR/PTEN co-mutated lung adenocarcinoma with lymph node metastases, which comprised adenocarcinoma admixed with SCLC. EGFR L858R and PTEN R130Q mutations were shared between the primary tumor and lymph node metastasis. Additionally, EGFR I744M mutation was shared between the adenocarcinoma and SCLC components in the lymph node metastasis, confirming spontaneous transformation from adenocarcinoma to SCLC. Furthermore, TP53 and RB1 mutations were detected only in the SCLC components of the lymph node metastasis. Immunohistochemically, complete absence of Rb expression in SCLC was observed, suggesting the loss of function of RB1. Our case clearly shows that EGFR/PTEN co-mutated lung adenocarcinoma transformed to SCLC in the lymph node without TKI-mediated evolutionary selection pressures.

The great escape: tumour cell plasticity in resistance to targeted therapy

The success of targeted therapies in cancer treatment has been impeded by various mechanisms of resistance. Besides the acquisition of resistance-conferring genetic mutations, reversible mechanisms that lead to drug tolerance have emerged. Plasticity in tumour cells drives their transformation towards a phenotypic state that no longer depends on the drug-targeted pathway. These drug-refractory cells constitute a pool of slow-cycling cells that can either regain drug sensitivity upon treatment discontinuation or acquire permanent resistance to therapy and drive relapse. In the past few years, cell plasticity has emerged as a mode of targeted therapy evasion in various cancers, ranging from prostate and lung adenocarcinoma to melanoma and basal cell carcinoma. Our understanding of the mechanisms that control this phenotypic switch has also expanded, revealing the crucial role of reprogramming factors and chromatin remodelling. Further deciphering the molecular basis of tumour cell plasticity has the potential to contribute to new therapeutic strategies which, combined with existing anticancer treatments, could lead to deeper and longer-lasting clinical responses.

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.

Lung adenocarcinoma with sarcomatoid transformation after tyrosine kinase inhibitor treatment and chemotherapy

OBJECTIVES

Lung cancers have various acquired resistance mechanisms that lead to treatment failure and disease progression, including secondary epidermal growth factor receptor (EGFR) exon 20 T790 M mutations, EGFR downstream or bypass pathway activation, and histologic transformation from adenocarcinoma to small cell carcinoma, squamous cell carcinoma, or sarcomatoid carcinoma.

MATERIALS AND METHODS

This study compared the pathological and immunohistochemical characteristics before and after sarcomatoid transformation. Six advanced cases of lung adenocarcinoma that developed sarcomatoid transformation after treatment were collected.

RESULTS

Five cases had classic EGFR mutations and one had a ROS1 rearrangement. The interval from initial diagnosis to sarcomatoid transformation ranged from 9 to 88 mo (median of 31.5 mo). The median survival after sarcomatoid transformation was 2.5 mo (1-16 mo). Before sarcomatoid transformation, all cases demonstrated typical adenocarcinoma features, including acinar, micropapillary, or solid/cribriform patterns, negative or weak focal vimentin staining, and strong E-cadherin expression. Histologic features of sarcomatoid transformation included giant cell features (6/6), loose cellular cohesion (6/6), strong staining for vimentin (6/6), decreased or lost E-cadherin expression (5/6), and high PD-L1 expression (5/6; one case demonstrated high PD-L1 staining at initial diagnosis). High MET expression and MET copy number gain (two samples with high polysomy and three with true amplification) were observed in five cases with EGFR mutation treated with tyrosine kinase inhibitors (TKI). One case exhibited MET amplification prior to the start of TKI treatment.

CONCLUSION

Sarcomatoid transformation is a type of lung cancer histologic evolution with a poor prognosis and a high proportion of cases with aberrant MET activation and PD-L1 expression.