Adenocarcinoma Research Articles (Page 1)

Claudin 18 isoform 2 (CLDN18.2) has emerged as a novel therapeutical target for HER2-negative, locally advanced, or metastatic gastroesophageal adenocarcinoma. However, reported prevalence rates vary widely (24-47%), underscoring the need for accurate population-specific data. This study investigates the CLDN18.2 prevalence in Spanish patients with gastroesophageal adenocarcinoma and explores its correlation with other biomarkers and clinicopathological factors. We retrospectively analyzed endoscopic biopsy samples from gastroesophageal adenocarcinoma patients across three Spanish institutions. CLDN18.2 expression was evaluated by immunohistochemistry using the Ventana CLDN18 (43-14A) assay and PS2+ scoring, with cases showing membranous 2+ or 3+ staining in ≥ 75% of tumor cells classified as positive. Clinicopathological and biomarker data were retrieved from medical records. CLDN18.2 was positive in 33% (89/270) of cases. Although histological type was not correlated with CLDN18.2 status, cases with poorly cohesive morphology exhibited heterogeneous staining, with a predominance of moderately and strongly stained cells. A weak to moderate inverse correlation was identified between signet ring cell content and CLDN18.2 staining (r = -0.29, p = 0.028). No significant differences were observed in clinical outcome. However, among patients with advanced-stage disease, CLDN18.2-positive intestinal tumors were associated with worse progression-free survival (HR 2.58, 95% CI 1.18-5.63; p = 0.029). These findings confirm a 33% prevalence of CLDN18.2 expression in the Spanish population, aligning with reports from other Western European cohorts. The significant heterogeneity in poorly cohesive cases and an inverse correlation with signet ring cell content pose diagnostic challenges for pathologists. Moreover, the association between CLDN18.2 positivity and worse progression-free survival in intestinal adenocarcinoma supports a potential role in tumor progression and metastasis, warranting further research.

RICTOR, a core component of the mTORC2 complex, regulates AKT signaling and has been implicated in tumor biology. While RICTOR amplification and overexpression have been reported, the mutational landscape of RICTOR and its molecular context in non-small cell lung cancer (NSCLC) remain insufficiently characterized. This study aimed to describe the prevalence and co-alteration patterns of RICTOR mutations in metastatic lung adenocarcinoma. We retrospectively analyzed 137 patients diagnosed with metastatic lung adenocarcinoma between 2018 and 2024. Genomic profiling was performed using next-generation sequencing (NGS). Pathogenic alterations were catalogued, and co-mutation patterns in RICTOR-mutant and wild-type tumors were compared. RICTOR mutations were identified in 15% (n = 20) of patients. These mutations were most frequently co-detected with EGFR (65%), KRAS (55%), and TP53 (45%) alterations. Uncommon EGFR variants, including G719X and exon 20 insertions, were enriched in the RICTOR-mutant subgroup. Additional co-occurring events included PIK3CA, STK11, KEAP1, HER2, and BRAF V600E, though at lower frequencies. Gene fusions such as ALK-EML4 and ROS1 rearrangements were rarely observed in RICTOR-mutant cases. RICTOR mutations in lung adenocarcinoma define a molecularly distinct subgroup characterized by preferential co-occurrence with EGFR, KRAS, and TP53, as well as a broader spectrum of genomic alterations. These findings support the view that RICTOR functions within complex oncogenic contexts and warrant further investigation in larger, multi-institutional cohorts.

Aberrant overexpression of AURKA (aurora kinase A) is strongly associated with various malignancies. However, limited research exists regarding its clinical significance and pathogenic mechanisms in lung adenocarcinoma. This study elucidates clinical correlations and provides experimental evidence supporting AURKA's potential as a therapeutic target for lung adenocarcinoma (LUAD). We analyzed AURKA expression levels and prognostic value using data from TCGA and GEO databases. qRT-PCR compared AURKA expression in LUAD tissues and adjacent normal specimens. siRNA-mediated knockdown efficiency was verified through western blotting and qRT-PCR. Cellular proliferation was assessed via CCK-8 assays and tumor ball assay, while migration capacity was evaluated using transwell chambers. Flow cytometry analyzed cell cycle progression and apoptosis. Phosphoproteomic sequencing identified downstream pathways, with western blot validation of key targets. The changes of tight junctions were observed by transmission electron microscopy, fluorescein isothiocyanate dextran 4kDa (FD4) permeation experiment and immunofluorescence. A subcutaneous xenograft model in nude mice evaluated AURKA's in vivo tumorigenic effects. Our work illustrated that Elevated AURKA expression correlated significantly with poor LUAD prognosis. AURKA silencing markedly suppressed A549 cell proliferation and migration capacity while inducing G2/M phase arrest and apoptosis. Phosphorylated protein sequencing shows that AURKA knockdown is closely related to Cortactin (CTTN) mediated tight junction. Meanwhile, Xenograft models demonstrated that AURKA knockdown substantially inhibited tumor growth and metastatic progression. It was concluded that AURKA serves as a prognostic biomarker in LUAD. Mechanistically, AURKA promotes tumor progression through Cortactin phosphorylation-mediated tight junction disruption. Our findings establish AURKA inhibition as a promising therapeutic strategy for LUAD management.

Second-line 5-FU plus nanoliposomal irinotecan versus FOLFOX/XELOX in metastatic pancreatic cancer after gemcitabine-nab-paclitaxel failure: a propensity score-matched analysis.

While multimodality therapy for locally advanced esophageal cancer evolves, neoadjuvant chemoradiation has been a longstanding treatment paradigm. Pathologic complete response (pCR) rates vary by histology: 25% for adenocarcinoma (AC) and up to 50% for squamous cell carcinoma (SCC). Long-term outcomes after pCR remain poorly understood but important to define as multiple treatment options emerge. We analyzed patients with cT2+/N+M0 esophageal AC or SCC treated with neoadjuvant chemoradiation and resection from an institutional database. Recurrence-free survival (RFS) and overall survival (OS) were assessed using Kaplan-Meier and multivariable Cox models. A risk score for recurrence was developed and validated using National Cancer Data Base data. Of 830 patients, 37.1% achieved pCR (n = 250/720, 34.2% for AC and n = 58/100, 58.0% for SCC). pCR was associated with prolonged OS (5-year OS: 56.2% versus 35.0% for residual disease, p < 0.001). pCR remained an independent predictor of OS after adjustment for known predictors of OS (HR 0.58, p < 0.001). Recurrence typically occurred within 2 years then plateaued, with 5-year RFS of 72.6% for AC and 83.0% for SCC. Clinical T3/T4, cN+, fewer lymph nodes examined, and AC histology were independently associated with worse RFS. A weighted risk score for recurrence was developed, which externally predicted OS after pCR in the NCDB (HR 1.12 per point, p < 0.001). Median OS was 7.8 years for cases with score 0-3 versus 5.7 years for cases with score 4-5. pCR after neoadjuvant chemoradiotherapy is a strong predictor of survival, but recurrence remains common. Further investigation into adjuvant therapies for high-risk pCR patients is needed.

Previous studies showed an increasing incidence of early-onset colorectal cancer (EOCRC) during a period when cancer registration guidelines were changed. None of these studies simultaneously compared the patterns in colorectal adenocarcinoma (ADC) and neuroendocrine neoplasms (NENs) according to age and stage extension. To describe patterns in colorectal cancer incidence according to histopathological type and tumor extension at diagnosis in individuals younger than 50 years compared with older patients. This cohort study used data from the French Network of Cancer Registries (FRANCIM) on inhabitants of 7 French administrative areas. The cohort included individuals newly diagnosed with invasive colorectal cancer from 2004 to 2021. This period covered the change in NEN classification published in 2013. Statistical analysis was conducted from November 2024 to March 2025. Age-specific incidence rates of ADC and NENs were primary outcomes. Incidence was calculated and modeled to estimate annual percent changes (APCs) using a flexible multivariable Poisson model. In a sensitivity analysis, Joinpoint regressions consolidated the results. A total of 63 780 patients (35 266 males [55.3%]; mean [SD] age, 63.8 [12.8] years) were diagnosed with all colorectal cancer histologic types (CRC-All). The incidence of EOCRC increased in females (APC, 2.9%; 95% CI, 1.6%-4.3%) and males (APC, 2.6%; 95% CI, 1.2%-4.0%) aged 15 to 39 years but remained stable in those aged 40 to 49 years. In both sexes and all ages, the rates of ADC did not vary while NEN rates increased. In EOCRC, the increase in NENs was marked from 2004 to 2013 (between 10.1% [95% CI, 4.0%-16.5%] per year and 12.6% [95% CI, 7.2%-18.2%] per year) and disappeared thereafter (ranging from -1.1% [95% CI, -1.9% to -0.2%] per year to -1.7% [95% CI, -3.0% to -0.4%] per year). It affected the incidence of colorectal cancer only for patients aged 15 to 39 years, for whom the proportion of NENs was high (29.7% [278 of 935]) compared with 5.7% (132 of 2333) of patients in the 40 to 49 years age class and 1.4% (856 of 60 512) of patients in the 50 years or older age class). In EOCRC, ADC M1 (distant metastasis) incidence increased in both sexes over the entire study period (between 1.2% [95% CI, 0.3%-2.1%] per year and 2.3% [95% CI, 1.0%-3.6%] per year between 2013 and 2021). In this cohort study, the 2013 change in NENs classification had a prominent role in EOCRC incidence patterns. Public health decision-makers should consider this artifactual increase.

The aim of this retrospective study was to investigate the relative frequency of R0 margin classification following excision of canine apocrine gland anal sac adenocarcinoma (AGASACA). Secondary aims were to establish if R0/R1 margins, or other dog or tumor characteristics, were prognostic. Retrospective cohort study. Seventy-four dogs that underwent AGASACA excision. Each tumor margin was classified as R0 or R1 from the histopathology report. Additional data relating to primary tumor characteristics, preoperative assessment, local recurrence, metastases and survival were collated from the medical record. The rate of R0 margin classification following AGASACA excision was 75.7%. An R1 margin classification was associated with increased risk of local recurrence (OR 23, p < .0001). Overall median survival time following surgery was 25 months (95% CI 21-33). Survival time was reduced in dogs with preoperative hypercalcemia (7.5 months, p = .012), presence of metastatic disease (17 months, p = .005) and lymphovascular invasion on histopathology (21 months, p = .021). Mitotic count (p = .0069) and absence of adjunct therapy (p = .0247) also reduced survival time. The R margin classification was clinically useful in predicting local recurrence. Preoperative hypercalcemia, lymphovascular invasion on histopathology, presence of metastatic disease, mitotic count, and absence of adjunct therapy all negatively affected survival. Achieving complete margins was feasible in most dogs undergoing AGASACA excision and reduced the risk of local recurrence. The R margin classification scheme was clinically useful when reporting histopathology of canine AGASACAs.

Brain metastasis, a leading cause of death in patients with lung adenocarcinoma (LUAD), arises from tumor cells adapting to the unique microenvironment of the brain through metabolic remodeling regulated by key oncogenes. Here, we aimed to determine the role of high mobility group protein box 3 (HMGB3) in regulating tumor cell metabolism to promote the progression and brain metastasis of LUAD. A LUAD cell model predisposed to brain metastasis was established, followed by differential gene expression analysis. HMGB3 expression was quantified via single-cell RNA sequencing (scRNA-seq) and immunohistochemistry, with clinical relevance assessed in two retrospective cohorts: the primary LUAD and the LUAD brain metastasis cohorts. Gene enrichment analysis of scRNA-seq and bulk RNA-seq data, along with Western blotting, were performed to identify HMGB3-associated pathways. Co-immunoprecipitation combined with mass spectrometry was used to detect HMGB3-interacting proteins. Gain-of-function, loss-of-function and rescue experiments targeting HMGB3 downstream pathways were conducted in vitro and in vivo. HMGB3 expression was significantly elevated in both primary LUAD lesions and brain metastatic foci, and its upregulation was strongly associated with poor prognosis in LUAD patients, as well as in those with concomitant brain metastasis. HMGB3 enhanced the migration, invasion, and epithelial-mesenchymal transition (EMT) capabilities of LUAD cells in vitro and promoted the development of brain metastasis in vivo. Mechanistically, HMGB3 recruited and interacted with single-stranded DNA-binding protein 1 (SSBP1), inducing its nuclear translocation and reprogramming mitochondrial metabolism. This process elevated cytoplasmic reactive oxygen species levels, which subsequently activated the phosphatidylinositol 3-kinase/protein kinase B (PI3K-Akt) signaling pathway through downregulating phosphatase and tensin homolog (PTEN), ultimately promoting tumor cell proliferation, migration, invasion, and EMT. This study demonstrated HMGB3 as a key regulator of the brain metastasis of LUAD, orchestrating tumor cells' metabolic adaptation to the brain microenvironment through modulation of mitochondrial metabolism, thereby offering potential therapeutic targets for LUAD brain metastases.

Background: Ketamine is an N-methyl-D-aspartate receptor antagonist traditionally used for dissociative sedation that has also been used for the treatment of pain. Ketamine can have a higher bioavailability when administered intranasally. Objective: To present a case in which intranasal (IN) ketamine was used for unpredictable, episodic, cancer-related neuropathic pain. Case Presentation: We present a 49-year-old patient with metastatic adenocarcinoma of the lung who presented to our outpatient palliative care clinic with uncontrolled severe episodic neuropathic pain of the lower extremity. Case Management: We prescribed compounded racemic ketamine 20–30 mg intranasally as needed at the onset of severe episodes of breakthrough pain, in addition to scheduled use of oral methadone and a buprenorphine patch for long-acting pain management. Case Outcome: The patient reported a decrease in frequency, intensity, and duration of episodic breakthrough pain with use of IN ketamine without any reported negative adverse effects. Conclusion: Low-dose compounded racemic IN ketamine may be a useful and safe adjunct in alleviating severe breakthrough pain in cancer patients in the outpatient setting.

Background Reliable biomarkers are urgently needed to predict response to immune checkpoint inhibitors in metastatic esophageal adenocarcinoma (mEAC). This study evaluated early circulating free DNA (cfDNA) dynamics as a predictor of treatment response and survival in patients receiving platinum-based chemotherapy plus Nivolumab. Methods In this prospective pilot study, 95 patients with mEAC were treated with Nivolumab and platinum-based chemotherapy. Plasma cfDNA levels were measured at baseline, Day 15, and Day 30 using digital droplet PCR. The primary outcome was objective treatment response; secondary outcomes included progression-free survival (PFS) and overall survival (OS). Tumor mutational burden (TMB), PD-L1 expression, liver metastasis, and ECOG status were also assessed. Results Patients with a cfDNA Day 30/Baseline ratio &amp;lt;0.4 had significantly improved median PFS (11 vs. 4 months) and OS (14 vs. 7 months) compared to those with ratios &amp;gt;0.8 (p for trend &amp;lt;0.001). Early decline in cfDNA correlated with treatment response. High TMB (≥10 mut/Mb) was independently associated with increased response (adjusted OR: 2.5, 95% CI: 1.2–5.2, p=0.015). ECOG &amp;gt;1 was inversely associated with response (adjusted OR: 0.35, p=0.01). PD-L1 expression and liver metastasis were not significantly predictive. Conclusion Early cfDNA kinetics—particularly a Day 30/Baseline ratio &amp;lt;0.4—strongly predicted response and survival in mEAC patients receiving chemoimmunotherapy. cfDNA monitoring offers a promising non-invasive tool for early treatment stratification and response assessment in this population.

N6-methyladenosine (m6A) modification has emerged as a common chemical modification in epigenetic regulation. However, whether this m6A modification is involved in glycolysis metabolism in pancreatic ductal adenocarcinoma (PDAC) remains elusive. Multiomics integration strategies, including metabolomics, m6A-seq and transcriptome sequencing, were utilized to evaluate the associations between m6A modifications and key processes of glucose metabolism in PDAC. Spontaneous PDAC mice (LSLKrasG12D/+, LSL-Trp53R172H/+, Pdx1-Cre; KPC) with FTO-conditional knockout and organoids were used to evaluate the effects of FTO stimulation on PDAC cell glycolysis and tumorigenesis. Series of in vivo and vitro functional analysis revealed that FTO promoted migratory capacity and glycolysis of PDAC cells. Mechanistically, FTO elevates the mRNA expression of the transcription factor C-Jun in a m6A-YTHDF2-dependent manner and further transcriptionally upregulates PFKM expression. Translational studies involving organoid models and xenograft tumor models revealed that the use of FTO inhibitors significantly suppressed PDAC growth. Our findings uncover that targeting the m6A-dependent FTO/C-Jun/PFKM glycolysis regulatory axis may be essential for the prevention and treatment of PDAC.

RIPK2/STAT3 signaling axis drives lung cancer metastasis through SNAIL activation: Molecular mechanisms and clinical implications.

The treatment of metastatic prostate cancer relies on the use of androgen deprivation therapy, which is associated with many side effects, including adverse cardiovascular outcomes. 177Lu-vipivotide tetraxetan ([177Lu]Lu-PSMA-617) is used in the treatment of prostate-specific membrane antigen-expressing metastatic castration-resistant prostate adenocarcinoma. We present the case of a patient with prostate cancer with numerous metastatic lesions who declined androgen deprivation therapy, chemotherapy, and local therapy to the prostate gland and instead received first-line systemic [177Lu]Lu-PSMA-617. He exhibited a significant response in both the primary cancer and its metastatic foci after 2 doses of the treatment.

To assess modified folinic acid/leucovorin, fluorouracil, irinotecan, oxaliplatin (FOLFIRINOX [mFFX]) versus gemcitabine/nab-paclitaxel (GnP) in de novo metastatic pancreatic ductal adenocarcinoma (PDAC) and explore predictive biomarkers. Patients were randomly assigned 1:1 to mFFX or GnP with exclusion of germline pathogenic variants in BRCA1/2 or PALB2. The primary end point was progression-free survival (PFS) between arms with 0.3 significance. The per-protocol (PP) population included patients who received one dose of chemotherapy. Pretreatment biopsies underwent whole-genome/transcriptome sequencing and patient-derived organoid (PDO) development, providing correlate recommendations at a molecular tumor board and outcomes assessed according to RNA signatures (basal-like v classical). Of 160 patients randomly assigned (80 mFFX, 80 GnP), 140 patients were in the PP population (71 mFFX, 69 GnP), with median follow-up of 8.3 months. The median PFS was 4.0 months for mFFX versus 5.3 months for GnP (hazard ratio [HR], 1.37 [95% CI, 0.97 to 1.92]; P = .069) in intention-to-treat. Median overall survival (OS) was 8.5 months with mFFX and 9.7 months with GnP (HR, 1.57 [95% CI, 1.08 to 2.28]; P = .017). Genomic data were generated in 94%, transcriptomes in 74%, and PDOs in 50%. The median PFS for those with basal-like was 3.0 (mFFX) and 5.5 (GnP) months (P = .17), and classical PDAC was 6.3 (mFFX) versus 5.4 (GnP) months (P = .36). The median OS in basal-like was 7.5 (mFFX) and 8.9 (GnP) months (P = .75) versus in classical OS was 9.7 (mFFX) and 13.9 (GnP) months (P = .047). Overall, 75 (54%) of patients received second-line treatment, 33/75 (44%) correlate-guided. The median time on second-line treatment was only 2.1 months with a median OS of 5.4 months for a correlate-guided choice versus 4.4 months on a standard chemotherapy approach (P = .45). In the phase II Pancreatic Adenocarcinoma Signature Stratification for Treatment-01 (PASS-01) trial population, PFS was similar between GnP and mFFX; however, OS and safety trends favored GnP. The second-line setting appears inadequate to offer precision choices, given the short survival observed.

Bacteria and tumor debris induced pancreatic cancer progression via the NF-κB signaling pathway.

27-hydroxycholesterol roles in respiratory disease pathogenesis.

Background: Regression of malignancy in the absence of cancer-directed therapy is an uncommon and poorly understood phenomenon. Its occurrence is particularly rare for pancreatic ductal adenocarcinoma (PDAC). The interaction between tumor and microenvironment may induce an immune response in which both innate and acquired immunity have been found to be implicated. An immunogenic tumor may promote antigen presentation and effector T cell activity, leading to cancer cell death and tumor inhibition. Case: We present the case of a 57-year-old man diagnosed three years ago with a borderline-resectable PDAC confirmed by biopsy. The patient received first-line 5-fluorouracil-based chemotherapy with progression of disease including new hepatic metastases. He then received twelve cycles of gemcitabine and nab-paclitaxel with successful reduction in the number and size of liver metastases. Upon patient request, a treatment holiday was initiated, during which his abdominal imaging showed continued tumor regression. After eleven months without any systemic therapy, there are no remaining metastases in the liver, and the primary pancreatic mass continues to recede. He currently remains on surveillance. Conclusion: Our patient’s rare clinical course raises questions including the optimal next steps in treatment, such as continued observation or local treatment such as surgical resection. The decision to continue observation results from our belief that minimal disruption of the tumor microenvironment (TME) may allow for continued control and cancer regression. More laboratory and clinical studies are imperative to understanding the physiological basis of sustained tumor regression after chemotherapy discontinuation and may impact real-world clinical decision-making. Additionally, the definition of spontaneous tumor regression may need revision to distinguish between prolonged therapeutic response and regression due to immunogenic features in the absence of prior therapy.

PurposePancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with a high mortality rate. For patients with metastatic PDAC (mPDAC) initially deemed unresectable, systemic chemotherapy followed by conversion surgery may offer an improvement in survival. This study aimed to compare survival between mPDAC patients undergoing conversion surgery versus chemotherapy alone, and identify factors associated with recurrence following conversion surgery.MethodsWe conducted a retrospective cohort study of patients with mPDAC treated with systemic chemotherapy at National Cheng Kung University Hospital, Taiwan, between September 2020 and January 2023. Patients who subsequently underwent conversion surgery were analyzed to identify factors associated with recurrence. Clinicopathologic, treatment, and surgical variables were extracted from medical records. Recurrence-free survival (RFS) was defined from the date of conversion surgery to recurrence or death. Survival outcomes were estimated using the Kaplan–Meier method and compared with the log-rank test. Cox proportional hazards regression with stepwise selection was applied to identify independent predictors of recurrence.ResultsAmong 151 patients who underwent chemotherapy, 33 subsequently received conversion surgery. In the patients who received conversion surgery, male sex (HR 4.33, 95% CI 1.60–11.72), tumor location in the head/uncinate process (HR 2.79, 95% CI 1.03–7.58), and regression grade 2 (HR 4.65, 95% CI 1.41–15.30) were significantly associated with worse RFS.ConclusionAmong patients with mPDAC who underwent conversion surgery after chemotherapy, several factors were independently associated with shorter RFS, including male sex, tumor location in the pancreatic head/uncinate process, and histologic regression grade 2.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00432-025-06353-0.

Gene expression studies are fundamental in molecular biology, offering insights into development, disease progression, and therapeutic targets. To address the need for precise analysis of large datasets, we developed THRESHOLD, a novel tool that introduces the concept of gene saturation. Unlike traditional methods focused on absolute or binary expression levels, THRESHOLD quantifies the consistency of gene expression across patients, revealing co-regulation patterns critical for understanding disease mechanisms and stratifying patients by molecular signatures. The tool offers several features, including user-defined parameters, statistical comparisons, and interactive data visualization. THRESHOLD has uncovered compelling insights into disease progression using TCGA cancer datasets. For instance, bladder urothelial carcinoma demonstrated increasing upregulated gene saturation in progressive cancer stages (P < .00001). Moreover, THRESHOLD identified heightened gene saturation in patients with earlier onset of prostate adenocarcinoma (P < .0001) and revealed a critical fusion transcript, SLC45A2-AMACR, implicated in prostate adenocarcinoma progression, recurrence, and metastasis. Additionally, novel biomarkers and potential candidates for drug therapies were identified through protein–protein interaction networks and functional analyses of saturation data in colon adenocarcinoma and breast invasive carcinoma. THRESHOLD offers a new approach for studying gene expression dynamics and patient stratification. The tool is publicly available at Zenodo: https://zenodo.org/records/15287195.

Patients with metastatic lung adenocarcinoma (mADC) harboring EGFR-activating mutations can benefit from first-line Osimertinib, but acquired resistance inevitably occurs. Different resistance mechanisms, on- and off-target, have been described. Here, we evaluated the prevalence of phenotypic transformation as a resistance mechanism in a consecutive series of EGFR-mutated mADC, diagnosed at our institution, and on the basis of literature data. A consecutive 3-year series of non-small cell lung cancer (NSCLC) was reviewed according to histological and molecular characteristics. A total of 100 mADCs harboring EGFR exon-19 deletions (61 cases) and the p.(L858R) mutation (39 cases) were selected. All cases were treated by first-line Osimertinib. The prevalence and type of phenotypic transformation were evaluated in patients with available rebiopsy at the time of first-line progression. A total of 32 mADC patients underwent rebiopsy upon first-line Osimertinib progression, and 23 cases had EGFR exon-19 in-frame deletions and 9 p.(L858R) mutations. Four cases showed a phenotypic transformation after a median of 15 months from the start of Osimertinib treatment. All these cases harbored EGFR exon-19 deletions and TP53 pathogenic mutations on diagnostic tumor tissues. Three cases switched to small cell lung cancer histology; in one case, a MET amplification was also detected on rebiopsy. One case changed to spindle cell carcinoma. All cases maintained the initial activating EGFR alteration. For three cases, liquid biopsy was performed at the time of progression: one was negative, one presented only an EGFR exon-19 deletion, and one presented only a MET amplification. In our study, phenotypic transformation had a considerable prevalence among EGFR-positive mADC patients treated by first-line Osimertinib. Different types of histological changes were detected as the only resistance mechanism except for one case with a simultaneously acquired MET amplification. Moreover, all cases harbored TP53 alterations, influencing treatment response. Despite the usefulness of liquid biopsy, rebiopsy should be executed whenever possible. Indeed, it remains the only tool for assessing histological transformation, which greatly impacts prognosis and treatment decisions.