Bronchiolar Adenoma: Expansion of the Concept of Ciliated Muconodular Papillary Tumors With Proposal for Revised Terminology Based on Morphologic, Immunophenotypic, and Genomic Analysis of 25 Cases

Bronchiolar adenoma with EGFR exon 19 deletion mutation: a case report and literature review

Background

Bronchiolar adenoma (BA) is a benign lung tumor characterized by nodular proliferation of bilayered bronchiolar-type epithelium with a continuous basal cell layer. The genetic characteristics of BA are not well understood. However, mutations commonly associated with lung adenocarcinoma, such as BRAF V600E, epidermal growth factor receptor (EGFR) mutations, and ALK rearrangements, have recently been identified in this context.

Case report

This report describes a case of BA in a 43-year-old male who presented with a mixed ground-glass opacity (mGGO) detected during a routine physical examination. The patient had excellent cardiopulmonary function and no other medical conditions. After evaluation, local surgical resection was performed. Intraoperative frozen section pathology initially suggested adenocarcinoma. However, postoperative immunohistochemical examination confirmed the diagnosis of BA. Next-generation sequencing (NGS) further revealed an EGFR exon 19 deletion mutation.

Conclusion

The histological morphology of highly differentiated small invasive adenocarcinomas and microinvasive adenocarcinomas closely resembles that of BAs in intraoperative frozen sections. Additionally, gene mutations linked to adenocarcinoma have been identified in BAs. The potential relationship between these two diseases warrants further investigation.

Uncommon Tumors of the Lung: Recently Described and Rediscovered Tumors

CONTEXT.—

The great majority of primary pulmonary neoplasms are represented by non-small cell carcinomas-adenocarcinoma and squamous cell carcinoma. In addition, there is another group of neoplasms such as those of neuroendocrine origin that also represent a meaningful subset of primary lung neoplasms. Basically, any other tumor that is not in these groups of tumors may represent an unusual lung neoplasm.

OBJECTIVE.—

To highlight more recently described unusual tumoral entities that may represent a challenge in diagnosis and that require awareness of their existence.

DATA SOURCES.—

This is a review of 3 different entities: bronchiolar adenoma, adenofibroma, and hemangioblastoma-like clear cell stromal tumor. These tumoral conditions are rare, and a review of the literature is presented. The most relevant morphologic, immunohistochemical, and molecular aspects of bronchiolar adenoma, adenofibroma, and hemangioblastoma-like clear cell stromal tumor are presented. The difficulty of arriving at an unequivocal diagnosis in small biopsies is highlighted.

CONCLUSIONS.—

The 3 entities represent uncommon tumors occurring primarily in the lung and a diagnostic challenge not only in biopsy specimens but also often in surgically resected specimens. The use of immunohistochemical stains and in some cases of molecular diagnostics is of aid in arriving at final interpretation.

Intraoperative frozen section diagnosis of lung specimens: An updated review

Intraoperative frozen section (FS) diagnosis is a critical step in the management of patients with pulmonary lesions, which provides guidance for surgical resection procedures. Intraoperative FS diagnosis requires a comprehensive approach that integrates clinical information, imaging findings, and histopathological evaluation. Effective communication between pathologists and surgeons is vital for achieving the best practice result. Intraoperative FS diagnosis faces new challenges in the era of new lung cancer screening strategy, changes in histological tumor classification and addition of new lung tumor entities. Below we discuss the challenges in pre-intraoperative assessment and intraoperative diagnosis of pulmonary nodules. Key considerations include clinical information and CT imaging findings. Multiple nodules require strategic sampling, focusing on the most malignant-appearing lesion. Intraoperative FS diagnosis involves recognizing growth patterns and cellular atypia that help distinction of preinvasive lesions, minimal invasive, and invasive tumor although it might be challenging. Distinguishing benign from malignant tumors is also discussed, with emphasis on histological and imaging features. Special considerations include spread through air spaces (STAS), margin assessment, lymphoproliferative disorders, infectious diseases, and benign or uncertain-behavior tumors.

Preoperative CT and Radiomics Nomograms for Distinguishing Bronchiolar Adenoma and Early-Stage Lung Adenocarcinoma

RATIONALE AND OBJECTIVES

Evaluating the capability of CT nomograms and CT-based radiomics nomograms to differentiate between Bronchiolar Adenoma (BA) and Early-stage Lung Adenocarcinoma (LUAD).

MATERIALS AND METHODS

In this retrospective study; we analyzed data from 226 patients who were treated at our institution and pathologically confirmed to have either BA or Early-stage LUAD. Patients were randomly divided into a training cohort (n=158) and a testing cohort (n=68). All CT images were independently analyzed and measured by two radiologists using conventional computed tomography. Clinical predictive factors were identified using logistic regression. Multivariable logistic regression analysis was used to construct differential diagnostic models for BA and early-stage LUAD, including traditional CT and radiomics models. The performance of the models was determined based on the area under the receiver operating characteristic curve, discrimination ability, and decision curve analysis (DCA).

RESULTS

Lesion shape, tumor-lung interface, and pleural retraction signs were identified as independent clinical predictors. The areas under the curve for the CT nomogram, radiomic features, and radiomics nomogram were 0.854, 0.769, and 0.901, respectively. Both the CT nomogram and the radiomics nomogram demonstrated good generalizability in distinguishing between the two entities. DCA indicated that the nomograms achieved a higher net benefit compared to the use of radiomic features alone.

CONCLUSION

The two preoperative nomograms hold significant value in differentiating between patients with BA and those with Early-stage LUAD, and they contribute to informed clinical treatment decision-making.

A case of peribronchiolar metaplasia of the lung appearing as a solid nodule on computed tomography

Peribronchiolar metaplasia is an uncommon lesion characterized by fibrosis and bronchiolar epithelial cell proliferation along the peribronchiolar alveolar walls, primarily in response to bronchiolar and peribronchiolar injuries. Peribronchiolar metaplasia usually appears as ground glass nodules or sub-solid nodules on computed tomography. However, we present an exceptional case of peribronchiolar metaplasia that appeared as a solitary solid nodule on computed tomography. A 62-year-old woman with conjunctival icterus was diagnosed with ampullary cancer and nodal metastasis. A solid predominant nodule (0.7 cm maximum diameter) in the left lower lobe was identified on computed tomography, requiring accurate differentiation between primary lung cancer and pulmonary metastasis. Due to the location, histological confirmation via transbronchial biopsy was not feasible. Hence, the patient underwent surgery for both diagnosis and treatment. The pathological findings revealed the growth of columnar epithelium containing ciliated cells replacing alveolar epithelium in the bronchioloalveolar wall with no malignant component. The final pathological diagnosis of the lesion was peribronchiolar metaplasia. This unique case highlights an atypical presentation of peribronchiolar metaplasia as a solitary solid nodule on computed tomography. Recognizing that peribronchiolar metaplasia can also manifest as solid nodules, as illustrated in our current case, is essential.

Bronchiolar adenoma/ciliated muconodular papillary tumor complicated by lymphoid interstitial pneumonia in a patient with Sjögren's disease: A case report and systematic review

Bronchiolar adenoma (BA)/ciliated muconodular papillary tumor (CMPT) is a rare pulmonary neoplasm, with less than 150 cases documented in the literature. We report a unique case of BA/CMPT complicated by lymphoid interstitial pneumonia (LIP) in a 55-year-old male with Sjögren's disease. This is the first documented instance of such a comorbidity. Through a systematic review of PubMed, we also summarize the demographic, clinical, radiological, histopathological, and treatment characteristics of CMPT.

Case of lung fine needle aspiration showing mucinous cells and extracellular mucin

Mucinous neoplasm with extracellular mucin can be challenging to interpret on fine needle aspiration and core biopsies. Determining the biologic origin of the mucin/mucinous cells, that is, benign/incidental versus neoplasm, invasive versus in situ, and primary versus metastatic tumors, requires a thorough multidisciplinary evaluation. The work up of these lesions includes morphologic analysis with ancillary immunohistochemical and/or molecular studies and correlation with clinical and imaging studies. This review outlines a practical approach to the diagnosis of mucinous lesions in the lung with comprehensive review of literature.

Ciliated Muconodular Papillary Tumors of the Lung Harboring STRN::ALK Fusion: Case Report and Review of the Literature

Ciliated muconodular papillary tumor (CMPT) is a rare pulmonary tumor, typically occurring in middle-aged and elderly individuals. The molecular mutation spectrum of CMPT remains insufficiently explored. Commonly known driver gene alterations include KRAS, BRAF, EGFR, and ALK rearrangement. This report details the clinicopathological features of 2 patients presenting with CMPT as pulmonary nodules during clinical examinations. Microscopic analysis revealed tumors with glandular or papillary structures, consisting of mucinous cells, ciliated columnar cells, and basal cells. Notably, both patients exhibited STRN::ALK fusion, a finding not previously associated with CMPT. STRN::ALK fusion serves as a target for therapy in various tumors, including non-small cell lung cancer, thyroid cancer, and colon cancer. Consequently, we conducted a review of relevant literature, summarizing the clinicopathological and molecular characteristics of CMPT to facilitate further research. Our insights enhance the understanding of this uncommon tumor and contribute to the expansion of its molecular alteration spectrum.

Alveolar Adenoma: A 20-Year Experience at a Western Balkan University Hospital and a Literature Review

Alveolar adenoma is a rare benign lung tumor. We report 5 patients within a 20-year period diagnosed with this rare tumor and its clinical and histopathological features, in order to emphasize its significance in differential diagnosis of other lung tumors. Alveolar adenoma was more frequently diagnosed in female patients (80%). The patients ranged in age from 52 to 68. Eighty percent of the patients had symptoms like dyspnea, and shoulder or back pain. Three patients underwent a video-assisted thoracoscopic surgery, while 2 patients underwent a thoracotomy in order to remove the tumor. The tumor was localized within the right upper lobe, right lower lobe, and left lower lobe in 40%, 40%, and 20% of patients, respectively. The tumor size ranged from 14 to 30 mm. A frozen section finding of all 5 tumors reported that the lesion was benign. In all analyzed tumors, immunohistochemical analysis showed positive expression of TTF-1 and pankeratin in surface epithelial cells, and Vimentin positivity and TTF-1 and pankeratin negativity in round stromal cells. Alveolar adenoma should be carefully considered in the differential diagnosis of solitary pulmonary nodules. Complete surgical removal of the lesion is widely used in its primary management.

High-efficiency EGFR genotyping using cell-free DNA in bronchial washing fluid

BACKGROUND

EGFR mutation testing is required for treatment of lung adenocarcinoma using epidermal growth factor receptor-tyrosine kinase inhibitor. However, the amounts of tumor tissue or tumor cells obtained by bronchoscopy are often insufficient. Bronchial washing fluid, obtained by lavage with saline after tumor biopsy or brushing, and the supernatant of bronchial washing fluid are thought to contain cell-free DNA that would be potentially applicable for EGFR testing.

METHODS

From among patients with suspected adenocarcinoma or non-small cell lung carcinoma diagnosed from biopsy or surgical specimens at the University of Tsukuba Hospital between 2015 and 2019, cell-free DNAs from 80 specimens of supernatant of bronchial washing fluid (50 with EGFR mutation and 30 with wild type EGFR) and 8 blood serum samples were examined for EGFR mutation using droplet digital PCR.

RESULTS

Among the 50 patients harboring EGFR mutation, the rate of positivity for cell-free DNA extracted from supernatant of bronchial washing fluid was 80% (40/50). In nine of the EGFR mutation-positive cases, tumor cells were not detected by either biopsy or cytology, but the mutation was detected in four cases (4/9, 44%). Comparison of the cell-free DNA mutation detection rate between supernatant of bronchial washing fluid and blood serum in six cases showed that mutations were detected from the former in all cases (6/6, 100%), but from the latter in only one case (1/6, 17%).

CONCLUSIONS

Using supernatant of bronchial washing fluid samples, the detection rate of EGFR mutation was high, and EGFR mutations were detectable even when no tumor cells had been detectable by biopsy or cytology. Supernatant of bronchial washing fluid might be an effective sample source for EGFR mutation testing.

Clinicopathological analysis of bronchiolar adenoma combined with lung adenocarcinoma: Report of eight cases and literature review

AIMS

To investigate the clinicopathological characteristics and potential diagnostic pitfalls of bronchiolar adenoma (BA) combined with lung adenocarcinoma (LUAD) in the same lesion.

METHODS

We analyzed eight cases of BA combined with LUAD from our hospital pathology department between July 2020 and January 2022, and summarized their clinical data, radiological features, histopathological characteristics and immunohistochemical phenotypes.

RESULTS

Upon macroscopic examination, the lesions were characterized by gray-white or gray-brown solid nodules with well-defined borders, measuring 0.6-1.8cm in maximum diameter. The incidence of proximal-type BA (6/8) was higher than that of distal-type BA (2/8), and they combined with different stages of LUAD, including adenocarcinoma in situ, minimally invasive adenocarcinoma, invasive adenocarcinoma, and invasive mucinous adenocarcinoma (IMA). Immunohistochemistry showed that cytokeratin 5/6 and P40 were positive in the continuous basal cell layer in BA, but only scattered positive basal cells were seen at the junction of BA and LUAD. TTF-1 was positive in proximal-type BA ciliated cells in five cases and in LUAD cells in seven cases, and weakly positive in some basal cells. One case of IMA and mucinous cells of BA were TTF-1 negative. There was partially positive Napsin-A expression in BA luminal cells and LUAD cells of all cases except IMA.

CONCLUSION

There is no obvious boundary when BA and LUAD are in the same lesion. The luminal epithelial cells in the area where the two components migrate toward each other are atypical and lack a continuous underlying basal cell layer. Microscopic diagnosis should be aided by immunohistochemistry.

Endobronchial Glandular Papilloma With Atypical Histologic Characteristics: A Case Report and Literature Review

Papilloma of the lung is a rare benign entity and can be solitary or multiple. Solitary papilloma is subclassified into three categories: squamous papilloma, glandular papilloma, and mixed squamous and glandular papilloma. Glandular papilloma is the rarest subtype among them and occurs mostly in the sixth decade without any relation to smoking, syndrome, or infection. Histology is characterized by mixture of pseudostratified, columnar, nonciliated, mucinous epithelium-lined papillary fronds without any mitoses, necrosis, or atypia. The differential diagnosis can be broad depending upon the histologic features present in a particular case and may include both benign and malignant entities. We present here a patient with glandular endobronchial papilloma showing unusual clinical history and atypical histologic features, which required extensive immunohistochemical evaluation to establish a final diagnosis.

Bronchiolar adenoma/ciliated muconodular papillary tumour: advancing clinical, pathological, and imaging insights for future perspectives

Bronchiolar adenoma/ciliated muconodular papillary tumour (BA/CMPT) is a benign peripheral lung tumour composed of bilayered bronchiolar-type epithelium containing a continuous basal cell layer; however, the similarities in imaging and tissue biopsy findings at histopathology between BA/CMPT and malignant tumours, including lung adenocarcinoma, pose significant challenges in accurately diagnosing BA/CMPT preoperatively. This difficulty in differentiation often results in misdiagnosis and unnecessary overtreatment. The objective of this article is to provide a comprehensive and systematic review of BA/CMPT, encompassing its clinical manifestations, pathological basis, imaging features, and differential diagnosis. By enhancing healthcare professionals' understanding of this disease, we aim to improve the accuracy of preoperative BA/CMPT diagnosis. This improvement is crucial for the development of appropriate therapeutic strategies and the overall improvement of patient prognosis.

Pulmonary invasive mucinous adenocarcinoma

Invasive mucinous adenocarcinoma (IMA) is a relatively rare subtype of lung adenocarcinoma, composed of goblet and/or columnar tumour cells containing abundant intracytoplasmic mucin vacuoles. While a majority of IMAs are driven by KRAS mutations, recent studies have identified distinct genomic alterations, such as NRG1 and ERBB2 fusions. IMAs also more frequently present as a pneumonic-like pattern with multifocal and multilobar involvement, and comparative genomic profiling predominantly shows a clonal relationship, suggesting intrapulmonary metastases rather than synchronous primary tumours. Accordingly, these unique features require different therapeutic approaches when compared to nonmucinous adenocarcinomas in general. In this article, we review recent updates on the histopathological, clinical, and molecular features of IMAs, and also highlight some unresolved issues for future studies.

What's new in benign lung tumours?

While lung cancer is one of the most common malignancies routinely encountered by pathologists, benign pulmonary neoplasms are quite rare. However, it is important for pathologists to be familiar with the typical diagnostic features of benign lung tumors to avoid confusing them with malignant morphological mimics. There have also been intriguing discoveries in the genetics of benign pulmonary neoplasms in the past decade. This review will cover several of the most common benign lung tumors, including the diagnostic categories of pulmonary adenomas, bronchial papillomas, and benign mesenchymal tumors, with discussion of the current classification, differential diagnosis, and current knowledge regarding genetic drivers.

Recent developments in the pathology of primary pulmonary salivary gland-type tumours

Primary pulmonary salivary gland-type tumours are rare neoplasms that are thought to arise from seromucinous glands that are located in the submucosa of large airways. These neoplasms have clinical and pathologic features that are distinct from other pulmonary neoplasms. The majority of primary pulmonary salivary gland-type tumours are malignant, with the most common entities being mucoepidermoid carcinoma, adenoid cystic carcinoma, and epithelial-myoepithelial carcinoma. Less commonly seen are myoepithelial carcinoma, hyalinizing clear cell carcinoma, acinic cell carcinoma, secretory carcinoma, salivary duct carcinoma, intraductal carcinoma, and polymorphous adenocarcinoma. Benign salivary gland-type tumours of the lung include pleomorphic adenoma and sialadenoma papilliferum. Morphologic, immunophenotypic, and molecular features of these neoplasms are largely similar to salivary gland tumours elsewhere, and therefore the exclusion of metastatic disease requires clinical and radiologic correlation. However, the differential diagnostic considerations are different in the lung. The distinction of salivary gland-type tumours from their histologic mimics is important for both prognostication and treatment decisions. Overall, salivary gland type-tumours tend to have a more favourable outcome than other pulmonary carcinomas, although high-grade variants exist for many of these tumour types. Recent advances in our understanding of the spectrum of salivary gland-type tumours reported in the lung and their diversity of molecular and immunohistochemical features have helped to refine the classification of these tumours and have highlighted a few differences between salivary gland-type tumours of the lung and those primary to other sites.

Bronchiole adenoma/pulmonary ciliated mucinous nodular papillary tumor: Case series and literature review

OBJECTIVE

To analyze the clinical-pathological characteristics of 3 cases of bronchiolar adenoma/pulmonary ciliary mucinous nodular papillary tumors, and to improve the understanding of bronchiolar adenoma (BA)/ciliated muconodular papillary tumors (CMPT) (bronchiolar adenoma/ciliated muconodular papillary tumor).

METHODS

Retrospective analysis was done on the clinical information, diagnosis, and treatment of 3 instances of BA/CMPT at the Second People's Hospital of Weifang City. By scanning the CNKI, Wanfang, VIP database, and Pubmed database using the English key words "bronchiolar adenoma, ciliated muconodular papillary tumor," respectively patients with comprehensive clinical data were gathered, and studies from January 2002 to August 2021 that were relevant to the patients were examined.

RESULTS

A total of 35 articles and 71 instances were found, including 3 cases in our hospital, for a total of 74 cases. There were 31 males and 43 females among them, ranging in age from 18 to 84 years (average 63 years), and 15 cases had a smoking history. The majority of them were discovered by physical examination and had no clinical symptoms. The majority of the imaging revealed solid nodules with variable forms, with some ground-glass nodules displaying vacuole and bronchial inflation signs. BA/CMPT are generally gray-white, gray-brown solid nodules with obvious boundaries but no envelope with a maximum dimension of 4 to 45 mm (average 10.6 mm) on gross examination. Acinar, papillary, and lepidic formations can be seen under the microscope at high magnification; the majority of these structures are made up of tripartite epithelial components, including basal cells, mucous cells, ciliated columnar cells, and alveolar epithelial cells, demonstrating a variety of combinations. An important basis for diagnosis in immunohistochemistry is the continuous positive basal cell layer that is shown by p63, p40, and CK5/6. BRAF and epidermal growth factor receptor are the genes that are most frequently mutated. All of the patients showed no signs of metastasis or recurrence during follow-up period.

CONCLUSION

BA/CMPT is a rare benign tumor of lung epithelium. Because imaging and intraoperative cryosection diagnosis are easy to be misdiagnosed as malignant, it is necessary to further improve understanding and improve immunohistochemistry and genetic examination.

Clinicopathological features and genomic analysis of bronchiolar adenoma

BACKGROUND

Bronchiolar adenoma (BA) is a rare tumor of the bronchioles with a double-layer structure, including the basal cell layer and the superficial cell layer, and it has a good prognosis. However, the concept of a putative variant of BA has been proposed in the recent literature.

METHODS

Data on 17 cases of BA were collected from our center. The clinical data, morphology, immunophenotype, and molecular changes were retrospectively analyzed. We also collected the molecular changes in BA reported in the previous literature and summarized the putative driver mutations of BA.

RESULTS

Out of 17 BAs, 13 were classic cases with a double-layer structure, including 9 proximal-type and 4 distal-type BAs. Of note, we also identified 3 cases that lacked a continuous basal cell layer, including 2 cases of mixed-type BA with monolayered lesions (basal cells were undetected in some areas) and 1 case of a monolayered BA-like lesion (basal cells were completely undetected). The immunohistochemical findings of monolayer cell lesions were closer to those of minimally invasive adenocarcinoma. We also found one case in which BA transformed into invasive adenocarcinoma accompanied by mutations in the TP53, JAK2, NF1 and RB1 genes. Combined with the previous literature, the most common putative driver gene mutations in 62 BA lesions were EGFR (25/62; 41%) and BRAF (21/62; 34.4%).

CONCLUSION

Typical BA has a double-layer cell structure; however, there is also a putative variant of BA, which has a monolayer cell structure and lacks the basal cell layer. Transformation from BA into invasive adenocarcinoma is unusual but can occur.

Clinicopathological Analysis of Bronchiolar Adenoma Lined Purely by Mucinous Luminal Cells

Bronchiolar adenoma (BA) is a rare lung tumor that has recently been clearly named, including the previous ciliated muconodular papillary tumor (CMPT) and the so-called nonclassical CMPT. The most prominent histological feature of BA is a double-layer cell structure composed of a continuous basal cell layer and a luminal cell layer. BA lined purely by mucinous luminal cells is very rare, and only one case has been reported in the English literature. This type of BA can easily be misdiagnosed as early mucinous adenocarcinoma. This article analyzes the clinicopathological characteristics of a newly discovered case of BA lined purely by mucinous luminal cells and fully integrated with the literatures.

Multiple bronchiolar adenomas/ciliated muconodular papillary tumors of the bilateral lung with tumor budding and potential malignant transformation into squamous cell carcinoma: a case report and literature review

Background

Bronchiolar adenoma (BA)/ciliated muconodular papillary tumor (CMPT) is a rare lung tumor characterized by ciliated, mucous and basal cells. Recently, some cases of driver mutations or malignant transformations have been reported. However, the nature of BA/CMPT remains controversial. Here, we report a case of bilateral pulmonary multiple BAs with tumor budding and squamous metaplasia.

Case Description

A 55-year-old man presented with multiple small nodules in the lower lobes of the bilateral lungs on physical examination 7 years prior. During the past 3 years of regular follow-up, some nodules had slightly enlarged. Because the nodules were mostly solid, the patient underwent video-assisted thoracoscopic segmentectomy of the left lower lung. A postoperative pathological diagnosis of BA was made. In all lesions, the fusion and mutation of major driver genes were not detected by next-generation sequencing (NGS). No recurrence or metastasis was observed after 37 months of follow-up. Notably, all five resected lesions were BA/CMPT, and one lesion was accompanied by squamous metaplasia and tumor budding.

Conclusions

Our report found that BA/CMPT with squamous metaplasia and tumor budding has the potential to transform into lung squamous cell carcinoma, expanding its connection with malignant transformation. Smoking may be one of the risk factors. We also found that BA/CMPT can be multiple lesions rather than a solitary lesion.

Canadian Consensus Recommendations on the Management of KRAS G12C-Mutated NSCLC

Activating mutations in Kirsten rat sarcoma viral oncogene homologue (KRAS), in particular, a point mutation leading to a glycine-to-cysteine substitution at codon 12 (G12C), are among the most frequent genomic alterations in non-small cell lung cancer (NSCLC). Several agents targeting KRAS G12C have recently entered clinical development. Sotorasib, a first-in-class specific small molecule that irreversibly inhibits KRAS G12C, has since obtained Health Canada approval. The emergence of novel KRAS-targeted therapies warrants the development of evidence-based consensus recommendations to help clinicians better understand and contextualize the available data. A Canadian expert panel was convened to define the key clinical questions, review recent evidence, and discuss and agree on recommendations for the treatment of advanced KRAS G12C-mutated NSCLC. The panel agreed that testing for KRAS G12C should be performed as part of a comprehensive panel that includes current standard-of-care biomarkers. Sotorasib, the only approved KRAS G12C inhibitor in Canada, is recommended for patients with advanced KRAS G12C-mutated NSCLC who progressed on guideline-recommended first-line standard of care for advanced NSCLC without driver alterations (immune-checkpoint inhibitor(s) [ICIs] +/- chemotherapy). Sotorasib could also be offered as second-line therapy to patients who progressed on ICI monotherapy that are not candidates for a platinum doublet and those that received first-line chemotherapy with a contraindication to ICIs. Preliminary data indicate the activity of KRAS G12C inhibitors in brain metastases; however, the evidence is insufficient to make specific recommendations. Regular liver function monitoring is recommended when patients are prescribed KRAS G12C inhibitors due to risk of hepatotoxicity.

Mucous Gland Adenoma of the Lung: A Neoplastic Counterpart of Mucinous Bronchial Glands

Mucous gland adenoma (MGA) is a rare benign tumor that usually arises in the proximal airway and consists of mucus-secreting cells resembling bronchial glands. Here, we report 2 cases of MGAs and describe their morphologic, immunohistochemical, and molecular profiles in comparison with 19 pulmonary tumors of 5 other histologic types with mucinous cells (invasive mucinous adenocarcinoma, mucoepidermoid carcinoma, mixed squamous cell and glandular papilloma, bronchiolar adenoma/ciliated muconodular papillary tumor, and sialadenoma papilliferum). Two MGAs were found in 1 male patient and 1 female patient, located in the bronchus and trachea, respectively. One MGA was examined by RNA sequencing, and no putative driver mutations (including BRAF, KRAS, and AKT1 mutations) or gene fusions were identified. In another case of MGA, V600E mutations of BRAF and E17K mutations of AKT1 were not detected by allele-specific real-time PCR or digital PCR, respectively. However, a gene expression analysis revealed that the MGA presented a specific RNA expression profile with multiple genes enriched in the salivary gland. The gene expression of NKX3.1 was significantly higher in the MGA case in comparison to normal control lungs (P < .001). We then examined NKX3.1 immunohistochemistry for 2 MGAs and 19 tumors of 5 other histologic types. NKX3.1 was positive in MGA (2/2, 100%), whereas all constituent cells, including mucinous cells, were negative for NKX3.1 in other histologic types (0%, 0/19). In normal lung tissue, NKX3.1 was positive for mucinous acinar cells of the bronchial glands. In conclusion, the gene expression profile, taken together with the histologic similarity between MGA and bronchial glands, and the preferred location of the tumors (proximal airways with submucosal glands) suggest that MGA is a neoplastic counterpart of mucinous bronchial glands. NKX3.1 immunohistochemistry can be a sensitive and specific ancillary marker that distinguishes MGA from other histologic mimics.

Clinicopathologic Features and Frozen Diagnostic Pitfalls of Bronchiolar Adenoma/Ciliated Muconodular Papillary Tumors (BA/CMPTs)

To describe the histologic features of bronchiolar adenoma/ciliated muconodular papillary tumors (BA/CMPTs) and analyze the pitfalls in diagnosis from frozen sections. A total of 208 frozen and permanent sections of BA/CMPTs from Shanghai Chest Hospital from July 2018 to July 2021 were retrospectively analyzed. The median age of BA/CMPT patients was 65 years (15 to 79 y), and women accounted for 61.62% (122/198). The median size of BA/CMPTs was 0.6 cm (range 0.2 to 2 cm), of which 88.94% were small (≤1 cm, 185/208). In terms of location, the right lower lobe accounted for 44.23% (92/208), and the left lower lobe accounted for 33.65% (70/208). In 10 patients with 2 independent BA/CMPTs, 5 lesions were located in the left lower lobe and 4 in the right lower lobe. A total of 86.06% of the CT images of BA/CMPT showed solid/subsolid nodules (179/208). Among 208 tumors, 68.75% were distal type (143/208), and 31.25% were proximal type (65/208). The qualitative error rate of frozen sections was 21.33% (32/150), of which the distal type accounted for 75% (24/32); most of them were misdiagnosed as invasive adenocarcinoma during frozen diagnosis. The frozen diagnosis of BA/CMPTs might result in misdiagnosis as invasive adenocarcinoma. A careful search for characteristics of BA/CMPT, such as bilayer epithelial cells with basal cells and a lack of cellular atypia and invasive growth patterns, may be helpful for frozen diagnosis.

A surgical case of ciliated muconodular papillary tumor of the lung

Ciliated muconodular papillary tumor (CMPT) is a rare type of tumor with both benign and malignant characteristics. Herein, we report the surgical case of a 65-year-old man with CMPT. Chest computed tomography revealed a solitary cavitary lesion with a maximum diameter of 11-mm in S10b of the right lower lung. A thoracoscopic lung wedge resection was subsequently performed. On microscopic examination, the tumor was composed of highly columnar cells with tubular-to-papillary and cystic growth patterns. On immunostaining, it was positive for the epidermal growth factor receptor. The tumor was diagnosed as a CMPT, exhibiting no recurrence after two years of follow-up.

Benign Lung Adenoma Mimicking an Adenocarcinoma With EML4-ALK Gene Fusion

Bronchiolar adenoma is a benign neoplastic process thought to be derived from the bronchiolar epithelium. Particularly in small biopsy specimens, this entity can mimic lung cancer with important implications for management. We report the case of a 33-year-old man with a right upper lobe lung nodule, with initial biopsy identifying an adenocarcinoma with EML4-ALK gene fusion. After being considered for neoadjuvant targeted therapy trials, the patient underwent a lobectomy. On postoperative histologic evaluation, the patient was found to have a benign bronchiolar adenoma.

Frequent EGFR exon 20 insertion in the so-called peripheral-type squamous cell neoplasm of uncertain malignant potential: a variant of bronchiolar adenoma or under-recognised entity?

INTRODUCTION

Herein we describe a series of rare peripheral pulmonary neoplasms temporarily termed "peripheral type squamous cell neoplasm of uncertain malignant potential (PSCN-UMP)" and investigate their relationship to bronchiolar adenoma (BA) and squamous cell carcinoma (SCC).

MATERIALS AND METHODS

The histologic and immunohistochemical features of 10 PSCN-UMPs and six BAs were compared. Whole exome sequencing (WES) and bioinformatics analysis were performed to further compare the genetic features of PSCN-UMPs, BAs, and NSCLCs.

RESULTS

All PSCN-UMPs were peripherally located and histologically characterised by the lepidic, nested, and papillary proliferation of relatively bland squamous cells, accompanied by entrapped hyperplastic reactive pneumocytes. The basal squamous cells coexpressed TTF1 and squamous markers. Both cellular components exhibited bland morphology and a low proliferative activity. The six BAs met the morphologic and immunophenotypic features of proximal-type BA. Genetically, driver mutations, including frequent EGFR exon 20 insertions, were found in PSCN-UMPs, while the KRAS mutation, BRAF mutation, and ERC1::RET fusion were detected in BAs. PSCN-UMPs also shared some alterations with BAs in mutational signatures, while copy number variants (CNV) were enriched in MET and NKX2-1 in PSCN-UMP and MCL1, MECOM, SGK1, and PRKAR1A in BA.

CONCLUSION

PSCN-UMPs exhibited the proliferation of bland squamous cells accompanied by entrapped pneumocytes and frequent EGFR exon 20 insertions, which showed distinct features from BAs and SCCs. Recognition of this specific entity will help to expand the morphologic and molecular spectrum of peripheral lung squamous neoplasms.

Malignant transformation of pulmonary bronchiolar adenoma into mucinous adenocarcinoma: A case report

BACKGROUND

Bronchiolar adenoma (BA) and ciliated muconodular papillary tumor are rare tumors that have bilayered cell proliferation and continuous expression of p40 and CK5/6 in the basal cell layer. Diagnosis is difficult because of the limited knowledge of these tumors and their morphological similarities to malignant tumors, including invasive mucinous adenocarcinoma, especially based on the histopathology of intraoperative frozen sections. These tumors are now considered to be benign neoplasms, with malignant transformation reported in only a few cases.

CASE SUMMARY

A 57-year-old woman presented with a 17.0 mm × 7.0 mm nodule in the lower lobe of the left lung. Hematoxylin-eosin staining and immunohistochemistry of a surgical specimen were performed. The tumor consisted of a BA area and a mucinous adenocarcinoma (MA) area. In the BA area, the tumor had a bilayered structure of luminal cells and basal cells. The basal cells were positive for CK5/6 and p40, but the MA area was negative for these biomarkers. The Ki-67 proliferation index was low (1%-2%). The patient was diagnosed with BA accompanied by MA, and had a favorable outcome.

CONCLUSION

The present study indicated that BA may be carcinogenic, and suggests that clinicians should be aware of its potential for malignant transformation.

Alveolar Adenoma With CD34 Diffusely Positive Stromal Cells: A Rare Case Report and Literature Review

Alveolar adenoma (AA) is a rare type of pulmonary neoplasm showing proliferation of alveolar epithelium and septal mesenchyme. Clinically, AA is asymptomatic, benign, and usually diagnosed incidentally. Surgical excision is curative. The etiology of AA is controversial and the pathogenesis is unknown, but it is thought to stem from type II pneumocytes and fibroblasts or fibroblast-like cells. The stromal cells in AA may show rare staining for CD34. Diffuse CD34 positivity of the interstitial stromal cells has rarely been described and reviewed. Here, we report a case of AA with strong and diffuse CD34 staining in the stromal cells.

Non-small cell lung carcinomas with diffuse coexpression of TTF1 and p40: clinicopathological and genomic features of 14 rare biphenotypic tumours

Thyroid transcription factor 1 (TTF1) and p40 are widely-utilized diagnostic markers of lung adenocarcinoma (LUAD) and squamous cell carcinoma (LUSC), respectively. Diffuse coexpression of TTF1 and p40 has been described in only rare case reports. In a multi-institutional study, we collected the largest cohort of these unusual tumours to-date (n = 14), with the goal of elucidating their clinicopathological and genomic characteristics. Lung tumours with diffuse coexpression (labelling 50-100% tumour cells) of TTF1 clone 8G7G3/1 and p40 clone BC28 were identified. Detailed clinicopathological and immunohistochemical parameters were analyzed. Eight tumours were analyzed by next-generation sequencing (NGS) and the results were compared to those in > 9 K LUAD and > 1 K LUSC. All tumours with diffuse TTF1/p40 coexpression were poorly differentiated non-small cell lung carcinomas (NSCLC), 42% of which had basaloid features. Some tumours exhibited focal keratinization (14%), napsin A and/or mucicarmine labelling (46%) or both squamous and glandular features (7%). NGS revealed a uniquely high rate of FGFR1 amplifications (70%) compared to either LUAD (0.7%, P < 0.0001) or LUSC (11%, P = 0.001). LUAD-type targetable driver alterations were identified in 38% of cases (one EGFR, two KRAS G12C). The tumours were clinically aggressive, exhibiting metastatic disease in most patients. Lung carcinomas with diffuse TTF1/p40 coexpression represent poorly differentiated NSCLCs with frequent basaloid features, but some show evidence of focal squamous, glandular or dual differentiation with a distinctly high rate of FGFR1 amplifications. The presence of targetable LUAD-type alterations (EGFR, KRAS G12C) emphasizes the importance of molecular testing in these tumours.

Comprehensive clinicopathological characteristics and mucin core protein expression profiles of bronchiolar adenoma

AIMS

Bronchiolar adenoma (BA) is a novel entity in the 2021 WHO classification of lung tumours. The expression profile of mucin core proteins in BAs is not clear. The aim of this study was to clarify the expression profiles of mucins and to validate the clinicopathologic and molecular features of BAs.

METHODS AND RESULTS

We examined the clinicopathological, immunohistochemical, and molecular features of 20 BAs. Our cohort comprised 10 proximal and 10 distal BAs. Only seven of 18 patients (39%) were accurately diagnosed with BA at the time of intraoperative consultation. The frequent genetic alterations were BRAF V600E (35%) and KRAS (30%) mutations, which were mutually exclusive. The expression of MUC1, MUC4, and MUC5B was observed in all cases and that of MUC5AC and MUC6 was observed in nine (45%) and five (25%) cases, respectively. MUC4 was diffusely expressed in 18 cases. In contrast, MUC1, MUC5AC, MUC5B, and MUC6 displayed a patchy expression pattern. These expression patterns were similar to that of bronchiolar epithelium in normal lung tissue. In addition, overexpression of MUC1 and MUC4 on the entire cell surface was not observed in any of the BAs, suggesting their benign nature.

CONCLUSION

BA commonly exhibits diffuse MUC4 and patchy MUC1 and MUC5B expression. Its unique expression pattern is probably attributed to mucin expression specific to the bronchiolar epithelium. These results confirm the clinicopathologic and molecular characteristics of BA, including the difficulty in intraoperative frozen section diagnosis and the broad morphologic spectrum of BA derived from the bronchiolar epithelium.

Bronchiolar adenoma/ciliated muconodular papillary tumor mixed with adenocarcinoma in situ in the same tumor

Bronchiolar adenoma (BA)/ciliated muconodular papillary tumor (CMPT) is defined as a benign tumor composed of epithelial and basal cells. Recently, some cases with driver mutations or malignant transformation have been observed. Thus, whether BA/CMPT is benign or malignant remains controversial. We herein report an extremely rare case of a 68-year-old woman with a CMPT accompanied by adenocarcinoma in situ (AIS). BA/CMPT existed inside the AIS. The BA/CMPT component did not show any driver mutations; however, the AIS component had an EGFR driver mutation in exon 19. The accumulation of cases and further studies are needed to discuss the malignant potential of BA/CMPT.

Bronchiolar adenoma-like tumour with monolayered component: Represent malignant transformation of bronchiolar adenoma? A series of five cases

Pulmonary bronchiolar adenoma (BA) is a rare lung tumour, it is unclear whether BA can develop into a malignancy. We presented five cases of BA-like tumour with monolayered components. This type of tumour may represent the malignant transformation of BA. Histologically, these tumours showed acinar and lepidic growth patterns. The acinar components were well-differentiated. The glandular tumour cells in these tumours contained cuboidal to columnar cells resembling type II pneumocytes or club (Clara) cells. A small number of mucinous cells were found in two cases. A few scattered ciliated cells were detected in three cases. The ciliated cells only existed in the bilayered components. The basal cells were highlighted by CK5/6 and p40 in a partial region of the tumour rather than in the entire tumour. The glandular tumour cells, including those in the bilayered component, were diffusely positive for TTF-1 and napsin-A. EGFR Exon19 deletions were found in four cases, and BRAF V600E mutation was found in one case. These BA-like tumours have biphasic morphological and molecular characteristics of BA and lung adenocarcinoma, suggesting distal-type BA may develop into a malignancy. More cases should be studied and especially cases with metastasis should be searched to further prove the malignant transformation.

A Nomogram Incorporating Tumor-Related Vessels for Differentiating Adenocarcinoma In Situ from Minimally Invasive and Invasive Adenocarcinoma Appearing as Subsolid Nodules

OBJECTIVES

To develop a nomogram incorporating the quantity of tumor-related vessels (TRVs) and conventional CT features (CCTFs) for the preoperative differentiation of adenocarcinoma in situ (AIS) from minimally invasive adenocarcinoma (MIA) and invasive adenocarcinoma (IAC) appearing as subsolid nodules.

METHODS

High-resolution CT target scans of 274 subsolid nodules from 268 patients were included in this study and randomly assigned to the training and validation groups at a ratio of 7:3. A nomogram incorporating CCTFs with the category of TRVs (CTRVs, using TRVs as categorical variables) and a final nomogram combining the number of TRVs (QTRVs) and CCTFs were constructed using multivariable logistic regression analysis. The performance levels of the two nomograms were evaluated and validated on the training and validation datasets and then compared.

RESULTS

The CCTF-QTRV nomogram incorporating abnormal air bronchogram, density, number of dilated and distorted vessels and number of adherent vessels showed more favorable predictive efficacy than the CCTF-CTRV nomogram (training cohort: area under the curve (AUC) = 0.893 vs. 0.844, validation cohort: AUC = 0.871 vs. 0.807). The net reclassification index (training cohort: 0.188, validation cohort: 0.326) and the integrated discrimination improvement values (training cohort: 0.091, validation cohort: 0.125) indicated that the CCTF-QTRV nomogram performed significantly better discriminative ability than the CCTF-CTRV nomogram (all p-value < 0.05).

CONCLUSIONS

The nomogram incorporating the QTRVs and CCTFs showed favorable predictive efficacy for differentiating AIS from MIA-IAC appearing as subsolid nodules and may serve as a potential tool to provide individual care for these patients.

Pathological components and CT imaging analysis of the area adjacent pleura within the pure ground-glass nodules with pleural deformation in invasive lung adenocarcinoma

Background

Pleural deformation is associated with the invasiveness of lung adenocarcinoma(LAC). Our study focused on the pathological components of the area adjacent pleura in pulmonary pure ground-glass nodules(pGGNs) with pleural deformations(P-pGGNs) confirmed to be invasive LAC without visceral pleural invasion (VPI) pathologically.

Methods

Computed tomography(CT) imaging features of nodules and pathological components of the area adjacent pleura were analyzed and recorded. Statistical analysis was performed for subgroups of P-pGGNs.

Results

The 81 enrolled patients with 81 P-pGGNs were finally involved in the analysis. None of solid/micropapillary group and none of VPI was observed, 54 alveoli/lepidics and 27 acinar/papillarys were observed. In P-pGGN with acinar/papillary components of the area adjacent pleura, invasive adenocarcinoma (IAC) was more common compared to minimally invasive adenocarcinoma (MIA, 74.07% vs. 25.93%; p < 0.001). The distance in alveoli/lepidic group was significantly larger (1.50 mm vs. 0.00 mm; p < 0.001) and the depth was significantly smaller (2.00 mm vs. 6.00 mm; p < 0.001) than that in acinar/papillary group. The CT attenuation value, maximum diameter and maximum vertical diameter was valuable to distinguish acinar/papillary group form alveoli/lepidic group(p < 0.05). The type d pleural deformation was the common pleural deformation in IAC(p = 0.028).

Conclusions

The pathological components of the area adjacent pleura in P-pGGN without VPI confirmed to be invasive LAC could included alveoli/lepidics and acinar/papillarys. Some CT indicators that can identify the pathological invasive components of the area adjacent pleura in P-pGGNs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-10043-2.

Pulmonary Sialadenoma Papilliferum and Its Mimics: What You Need to Know

Pulmonary salivary gland-type tumors (SGT) represent a small but distinct group of primary lung neoplasms. These types of tumors originate from the submucosal bronchial glands of the tracheobronchial tree. Pulmonary SGTs differ greatly in the incidence of individual tumors from salivary gland tumors of the head and neck. Additionally, the vast majority of pulmonary SGT are malignant. Recently, pathologic diagnosis has significantly improved with the application of molecular diagnostic technologies. However, the current knowledge of benign SGTs is limited; moreover, tumor diversity and overlapping morphological features of SGT represent diagnostic challenges such as correct tumor categorization and their accurate differentiation from malignant lesions. Compounding this inherent difficulty has been the recent introduction of new variants, including sialadenoma papilliferum (SP). Pulmonary SP is very rare, with limited reports available, and most of the initial diagnoses rendered so far were incorrect, resulting in inappropriate treatment. Several cases of SP have recently been reported. This review will serve to update practicing pathologists on the morphology, immunophenotype, and molecular characteristics of SP and its mimics.

Bronchiolar adenoma with unusual presentation: Two case reports

BACKGROUND

The clinicopathological features, immunohistochemical characteristics, and genetic mutation profile of two unusual cases of distal bronchiolar adenoma are retrospectively analyzed and the relevant literature is reviewed.

CASE SUMMARY

Case 1 was a 63-year-old female patient who had a mixed ground-glass nodule, with mild cells in morphology, visible cilia, and bilayer structures in focal areas. Immunohistochemical staining for P63 and cytokeratin (CK)5/6 revealed the lack of a continuous bilayer structure in most areas, and no mutations were found in epidermal growth factor receptor, anaplastic lymphoma kinase, ROS1, Kirsten rat sarcoma, PIK3CA, BRAF, human epidermal growth factor receptor-2 (HER2), RET, and neuroblastoma RAS genes. Case 2 was a 58-year-old female patient who presented with a solid nodule, in which most cells were observed to be medium sized, the nuclear chromatin was pale and homogeneous, local cells had atypia, and cilia were found locally. Immunohistochemical staining for P63 and CK5/6 showed no expression of these proteins in mild cell morphology whereas the heteromorphic cells showed a bilayer structure. The same nine genes as above were analyzed, and HER2 gene mutation was identified.

CONCLUSION

Some unresolved questions remain to be answered to determine whether the lesion is a benign adenoma or a part of the process of malignant transformation from benign adenoma of the bronchial epithelium. Furthermore, whether lesions with atypical bilayer structures are similar to atypical hyperplastic lesions of the breast remains to be elucidated. Moreover, clarity on whether these lesions can be called atypical bronchiolar adenoma and whether they are invasive precursor lesions is needed. Future studies should examine the diagnostic significance of HER2 gene mutation as a prognostic indicator.

Daily Practice Assessment of KRAS Status in NSCLC Patients: A New Challenge for the Thoracic Pathologist Is Right around the Corner

Simple Summary

RAS mutation is the most frequent oncogenic alteration in human cancers and KRAS is the most frequently mutated, notably in non-small cell lung carcinomas (NSCLC). Various attempts to inhibit KRAS in the past were unsuccessful in these latter tumors. However, recently, several small molecules (AMG510, MRTX849, JNJ-74699157, and LY3499446) have been developed to specifically target KRAS G12C-mutated tumors, which seems promising for patient treatment and should soon be administered in daily practice for non-squamous (NS)-NSCLC. In this context, it will be mandatory to systematically assess the KRAS status in routine clinical practice, at least in advanced NS-NSCLC, leading to new challenges for thoracic oncologists.

Abstract

KRAS mutations are among the most frequent genomic alterations identified in non-squamous non-small cell lung carcinomas (NS-NSCLC), notably in lung adenocarcinomas. In most cases, these mutations are mutually exclusive, with different genomic alterations currently known to be sensitive to therapies targeting EGFR, ALK, BRAF, ROS1, and NTRK. Recently, several promising clinical trials targeting KRAS mutations, particularly for KRAS G12C-mutated NSCLC, have established new hope for better treatment of patients. In parallel, other studies have shown that NSCLC harboring co-mutations in KRAS and STK11 or KEAP1 have demonstrated primary resistance to immune checkpoint inhibitors. Thus, the assessment of the KRAS status in advanced-stage NS-NSCLC has become essential to setting up an optimal therapeutic strategy in these patients. This stimulated the development of new algorithms for the management of NSCLC samples in pathology laboratories and conditioned reorganization of optimal health care of lung cancer patients by the thoracic pathologists. This review addresses the recent data concerning the detection of KRAS mutations in NSCLC and focuses on the new challenges facing pathologists in daily practice for KRAS status assessment.

Mucin distribution in bronchiolar adenoma/ciliated muconodular papillary tumor reveals organoid differentiation simulating the normal lung

Bronchiolar adenoma/ciliated muconodular papillary tumor is a lung neoplasm exhibiting various degrees of proximal and distal bronchiolar differentiation. Here, we evaluated distribution of MUC5AC and MUC5B in bronchiolar adenoma/ciliated muconodular papillary tumor for comparison with that seen in normal respiratory tract. In normal respiratory tract, MUC5AC was mainly distributed in large bronchi, while MUC5B was distributed in bronchi, bronchioles, and submucosal glands. In bronchiolar adenoma/ciliated muconodular papillary tumor, MUC5AC was primarily distributed in luminal cells of large airspaces, and MUC5B was distributed in luminal cells of small airspaces and mucinous glands, in addition to large airspaces, regardless of distal or proximal differentiation. In particular, MUC5B was distributed in non-mucinous club and ciliated cells in both the normal respiratory tract and bronchiolar adenoma/ciliated muconodular papillary tumor. These results indicate that MUC5AC and MUC5B distribution in bronchiolar adenoma/ciliated muconodular papillary tumor is similar to that seen in normal respiratory tract, suggestive of organoid differentiation simulating the normal lung.

A clinicopathologic and molecular analysis of five cases of bronchiolar adenoma with rare mutations

Bronchiolar adenoma (BA) is a rare benign lung tumor that shows proliferation of bland bronchiolar-type epithelium containing a continuous layer of basal cells. This tumor entity has been newly added to the recent World Health Organization (WHO) classification 5th edition. This entity encompasses a spectrum of lesions: the classic ciliated muconodular papillary tumor (CMPT) and the non-classic CMPT. Although BA is reported to have driver mutations including BRAF V600E, EGFR, and KRAS, the molecular profile of BA is still incompletely understood. Five resected BAs at our institutions were analyzed. The BA lesions were subdivided into two groups: three proximal-type BAs and two distal-type BAs. NRAS codon 12/13 mutation and EML4 exon 20-ALK exon 20 fusion were found in two of the three proximal-types. BRAF V600E mutation was found in one of the two distal-types. Two cases coexisted with lung adenocarcinoma, with EGFR exon 19 deletion and KRAS mutation, respectively. No recurrence was observed at a median of 12 months (range 2-84 months) of follow-up. BA has uncommon variants of mutation seen in lung adenocarcinoma. NRAS mutation and ALK fusion partner has not been reported previously. The present cases may reinforce the distinctive biology of BA from lung adenocarcinoma.

Unusual lung tumors-from morphology to genetics

Most pathologists are well versed in the diagnosis of lung cancer, given the common nature of the disease. Occasionally more unusual neoplasms are encountered in lung biopsies and resections, which may be difficult to distinguish from "run of the mill" lung cancer cases based on overlapping morphologic and immunophenotypic features. The accurate diagnosis of these rare entities is quite challenging and requires careful morphological examination paired with judicious use of ancillary immunohistochemical and genetic studies. Herein, the clinicopathological and genetic features of five unusual lung tumors will be reviewed, including thoracic SMARCA4-deficient undifferentiated tumor, NUT carcinoma, sclerosing pneumocytoma, primary pulmonary myxoid sarcoma/angiomatoid fibrous histiocytoma, and bronchiolar adenoma/ ciliated muconodular papillary tumor. Since recognition of these entities by pathologists is of increasing importance to guide prognosis and therapy, emphasis will be placed on practical tips to reach these rare diagnoses with confidence.

Updates in grading and invasion assessment in lung adenocarcinoma

The pathologic evaluation of lung adenocarcinoma, because of greater understanding of disease progression and prognosis, has become more complex. It is clear that histologic growth patterns reflect indolent and aggressive disease, resulting in clearer morphologic groups that can be the underpinning of a grading system. In addition, the progression of adenocarcinoma from a tumor that preserves alveolar architecture to one that remodels and effaces lung structure has led to criteria that reflect invasive rather than in-situ growth. While some of these are based on tumor cell growth pattern, aspects of this remodeling from desmoplasia to artifacts of lung collapse and sectioning, can lead to difficult to interpret patterns with lower reproducibility between observers. Such scenarios are examined to provide updates on new histologic concepts and to highlight ongoing problem areas.