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.

Background: The advent of immunotherapy has significantly improved survival outcomes in advanced non-small cell lung cancer (NSCLC). In this evolving context, salvage surgery has emerged as a potential curative strategy, despite the risk of serious complications. This study aimed to evaluate the safety and efficacy of surgical resection following chemo-immunotherapy in patients with initially unresectable NSCLC. Methods: We retrospectively analyzed patients with stage III–IVB NSCLC who underwent salvage surgery at our institution between January 2019 and June 2024. All cases were initially deemed unresectable by a multidisciplinary tumor board. Perioperative complications, complete (R0) resection rate, major pathologic response (MPR), complete pathologic response (pCR), progression-free survival (PFS), and overall survival (OS) were analyzed. Results: Twenty-one patients (thirteen males, eight females; median age: 68 years [IQR: 9]) were included. Reasons for initial unresectability were metastatic disease (28.6%), N2 bulky disease (14.3%), local invasiveness (33.3%), or a combination of factors (23.7%). Chemo-immunotherapy was administered in 19 patients (90.5%), while 2 (9.5%) received immunotherapy alone, with a median of four treatment cycles (IQR: 1). Complete (R0) resection was achieved in all patients (100%). Anatomical resections were performed in 17 patients (81%), predominantly lobectomies (66.7%). There were no intraoperative or major postoperative complications, and 30-day mortality was zero. Median hospital stay was 7 days (IQR: 4). pCR and MPR were achieved in 33.3% and 14.3% of patients, respectively. After a median follow-up of 17 months (IQR: 19), the estimated 3-year PFS and OS were 50.9% and 66.3%, respectively. Recurrences included locoregional (4.8%), distant (14.3%), and combined (14.3%). Cox regression analysis identified stage III at diagnosis (OR: 0.292; 95% CI: 0.093–0.912; p = 0.034) and achieved pCR or MPR (OR: 0.113; 95% CI: 0.013–0.959; p = 0.046) as independent predictors of improved PFS. Conclusions: Salvage surgery after chemo-immunotherapy in initially unresectable NSCLC appears to be a safe and effective strategy in selected patients, offering favorable pathological responses and encouraging mid-term oncologic outcomes.

Background. The Hippo pathway is the most frequently altered signaling in pleural mesothelioma (PM). Epithelioid PM (ePM) is associated with better outcome than non-epithelioid subtypes, but its prognosis can be heterogeneous. Here, we tried to stratify ePM using the expression levels of the Hippo-TEAD network. Methods. Thirty patients with ePM were included in this study. Tumors were stratified using the expression levels of 74 genes belonging to the Hippo-TEAD network and using the non-negative matrix factorization algorithm. Results were validated using ePM cases from the TCGA cohort. Alterations associated with the molecular subgroups were investigated using mutation and copy number alteration data from TCGA. Results. Two groups of ePM (i.e., HP1 and HP2) were identified and validated using TCGA data. HP2 comprises about one-third of tumors. These tumors are frequently high-grade (73% vs. 35%), have higher levels of downstream Hippo effectors (i.e., YAP1, WWTR1 and TEADs), lower levels of VSIR—which encodes for VISTA—and poorer PFS and OS. HP2 tumors commonly harbor homodeletions in Hippo core suppressors (25% vs. 3%), while no specific gene mutation or copy number alterations of Hippo genes was associated with the two groups. Conclusions. ePM can be stratified in prognostic subtypes based on the expression levels of the Hippo-TEAD network. Higher levels of downstream Hippo effectors are associated with poor response to platinum-pemetrexed doublet and worse OS. The stratification of ePM based on the activation of the YAP/TAZ-TEAD axis is an intriguing approach in the light of the inhibitors of this signaling that are currently under investigation.