Ciliated muconodular papillary tumors of the lung: a clinicopathologic analysis of 10 cases

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.

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.

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.

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.

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.

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.

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 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.

Ciliated muconodular papillary tumor of the lung: a case report and literature review

Background

Ciliated Muconodular Papillary Tumor (CMPT) was first reported in 2002, and fewer than 100 cases have since been reported. The prognosis after surgical resection is good, and recurrence has not been reported. However, it is easily misdiagnosed as adenocarcinoma. Summarizing the CT features of CMPT will help doctors better understand the disease.

Case presentation

Here, we report a rare and interesting case of ciliated muconodular papillary tumor. A 6-mm diameter solid nodule with slight lobulation, short spines, and subpleural indentation. Patients with clinical diagnosis of high-risk subpleural nodule in the left lung underwent thoracoscopic surgery. Most CMPT cases lack specific clinical manifestations and were found incidentally on physical examination or during a workup for other diseases. The disease was diagnosed through CT and biopsy, and it responded well to surgery.

Conclusions

This paper presents the detailed computed tomography features of CMPT to help prevent misdiagnosis. The typical manifestations of CMPT imaging as solid and partial nodules, nodules in subpleural or peripheral zones, and nodules contain cavities.

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.

The 2021 WHO Classification of Lung Tumors: Impact of advances since 2015

The 2021 World Health Organisation (WHO) Classification of Thoracic Tumours was published earlier this year, with classification of lung tumors being one of the chapters. The principles remain those of using morphology first, supported by immunohistochemistry and then molecular techniques. In 2015, there was particular emphasis on using immunohistochemistry to make classification more accurate. In 2021, there is greater emphasis throughout the book on advances in molecular pathology across all tumor types. Major features within this edition are 1) broader emphasis on genetic testing than in the 2015 WHO Classification, 2) a chapter entirely dedicated to the classification of small diagnostic samples, 3) continued recommendation to document percentages of histological patterns in invasive non-mucinous adenocarcinomas, with utilization of these features to apply a formal grading system, as well as using only invasive size for T-factor size determination in part lepidic non-mucinous lung adenocarcinomas as recommended by the 8^th Edition TNM Classification, 4) recognition of spread through airspaces (STAS) as a histological feature with prognostic significance, 5) moving lymphoepithelial carcinoma to squamous cell carcinomas, 6) update on evolving concepts in lung neuroendocrine neoplasm classification, 7) recognition of bronchiolar adenoma/ciliated muconodular papillary tumor (BA/CMPT) as a new entity within the adenoma subgroup, 8) recognition of thoracic SMARCA4-deficient undifferentiated tumor, and 9) inclusion of essential and desirable diagnostic criteria for each tumor.

Bronchiolar adenomas (BA) - A detailed radio-pathologic analysis of six cases and review of literature

Bronchiolar adenomas (BAs)/ciliated muco-nodular papillary tumors (CMPTs), are small, peripheral lung nodules arising predominantly in the elderly that follow a benign course. They can be mistaken for adenocarcinomas on frozen section. Immunohistochemistry (IHC) for basal cell markers highlights the continuous layer of basal cells underlying the tumor cells in BAs. BAs are further subdivided into proximal-type and distal type. Six BAs were retrieved from the pathology archives. The cases were classified based on morphology into proximal and distal BAs. The clinical and radiological features were reviewed. Immunohistochemistry and special stains were performed. The most common radiological picture of BA/CMPT was of a solid nodule with SUV_max < 3 as seen in 60% cases. 40% cases showed cavitation on CT. On histological examination, four cases were morphologically classified as proximal BAs and two as distal BAs. In proximal BAs, TTF1 was focally positive only in the basal cells in three of four. The mucin stained acidic. In distal BAs, TTF1 was diffusely positive in both basal and luminal cells. There was scant intracellular neutral mucin. Both the distal BAs had concomitant neuroendocrine tumors in the same lobe. Though the number of cases evaluated in this study is too low to be statistically significant, this study provides additional evidence to the concept of BA classification based on site specific histology and supplementary immunohistochemistry and reiterates the radiological features that may help distinguish it from malignant lesions.

A rare case of ciliated muconodular papillary tumor accompanied with adenocarcinoma in situ

BACKGROUND

Ciliated muconodular papillary tumor (CMPT) is an incredibly rare pulmonary tumor. Currently, little is known about CMPT, and it has not yet been classified by the World Health Organization. The clinical manifestation of CMPT is nonspecific and the diagnosis is only based on pathology. CMPT has been documented in limited reports as a benign tumor, thus the treatment is typically with surgical excision if a solid tumor is identifiable. The prognosis of CMPT is very positive, as no recurrence has been reported in the limited literature available. However, CMPT accompanied with adenocarcinoma in situ has not been reported previously in the literature.

CASE PRESENTATION

In this report, we presented a case of a 53-year-old male smoker with CMPT associated with adenocarcinoma in situ. This diagnosis was confirmed by pathological examination, including immunohistostaining. No solid resectable lesion was identified on CT scan; therefore, no surgery was performed. The patient's adenocarcinoma in situ was disseminated in both lungs, thus chemotherapeutic treatment with cisplatin and pemetrexed was given. The patient will be continually followed up closely on a wait-and-watch basis.

CONCLUSIONS

In summary, our report reveals a unique case of CMPT in conjunction with adenocarcinoma in situ, potentially revealing an association between CMPT and malignancy which has not been previously reported. More similar case studies will be beneficial to determine the authentic relationship between CMPT and adenocarcinoma in situ.

Bronchiolar Adenoma/Pulmonary Ciliated Muconodular Papillary Tumor

OBJECTIVES

To describe the histologic features that are helpful in the diagnosis of the rare bronchiolar adenomas/ciliated muconodular papillary tumors (BAs/CMPTs) during intraoperative consultation.

METHODS

Multi-institutional retrospective review of frozen sections of 18 BAs/CMPTs.

RESULTS

In 14 of 18 cases, BA/CMPT was the primary reason for sublobar lung resection, and in 4 cases, BA/CMPT was an incidental finding intraoperatively for resections performed for carcinoma in other lobes. There were 11 proximal-type/classic BAs/CMPTs and 7 distal-type/nonclassic BAs/CMPTs. Only 3 (16.7%) of 18 were correctly diagnosed at the time of frozen section, all of which were proximal type/classic. The remainder were diagnosed as adenocarcinoma (n = 7); invasive mucinous adenocarcinoma (n = 1); non-small cell lung carcinoma (n = 1); cystic mucinous neoplasm, favor adenocarcinoma (either mucinous or colloid type) (n = 1); favor adenocarcinoma, cannot exclude CMPT (n = 1); atypical proliferation (n = 2); mucinous epithelial proliferation (n = 1); and mucous gland adenoma (n = 1).

CONCLUSIONS

BA/CMPT can potentially be misdiagnosed as carcinoma during intraoperative consultation. On retrospective review of the frozen sections, the presence of the following may help to avoid misdiagnosis: a mixture of bland ciliated columnar cells, mucinous cells, and, most important, a basal cell layer, as well as a lack of necrosis, significant atypia, and mitoses.

Primary ciliated muconodular papillary tumor: A rare pulmonary disease and literature review of 65 cases

A ciliated muconodular papillary tumor (CMPT) or bronchiolar adenoma (BA) is a rather rare and unique type of lung tumor characterized by tripartite cellular components with a papillary-predominant structure including ciliated columnar cells, mucinous cells, and basal cells. Here, we present the case of a 64-year-old woman who was diagnosed with CMPT in our center. In addition to reporting the clinicopathological characteristics of this case, we also conducted whole exome sequencing (WES) to explore the underlying mechanism. According to current evidence, CMPTs tends to be benign or of low grade malignancy. However, this requires further validation.

Sialadenoma Papilliferum of the Bronchus: An Unrecognized Bronchial Counterpart of the Salivary Gland Tumor With Frequent BRAF V600E Mutations

Sialadenoma papilliferum (SP) is a rare benign tumor of the salivary glands, and only 3 unequivocal cases of SP arising in the bronchus have been reported. We herein describe the histomorphologic and molecular features of 4 bronchial SP cases and discuss the differential diagnosis of this entity and the relationship with its clinicopathologic mimics, in particular, glandular papilloma and mixed squamous cell and glandular papilloma (GP/MP). We encountered 2 male and 2 female patients with bronchial SP (mean: 66.8 y old). All 4 tumors arose in the central bronchus and were characterized by a combination of surface exophytic endobronchial papillary proliferation and a submucosal multicystic component with complex architecture. The neoplastic epithelium consisted predominantly of nonciliated stratified columnar cells with ciliated, squamous, and mucinous cells present focally. While 2 tumors (50%) harbored a BRAF V600E mutation by molecular and immunohistochemical analysis, similar to GP/MP, no KRAS, HRAS, AKT1, or PIK3CA mutations were detected in any of the cases. Two patients were treated with limited resection, while 2 patients underwent lobectomy based on the diagnosis of adenocarcinoma or possible squamous cell carcinoma in situ in the preoperative biopsy. All survived without recurrence or metastasis for 23 to 122 months after treatment. SP can develop in the central bronchus as the bronchial counterpart of the salivary gland tumor and should be considered in the differential diagnosis of endobronchial tumors. In addition, some histologic resemblance and frequent BRAF V600E mutation raise the possibility of SP and GP/MP being on the same disease spectrum.

Morphological, immunohistochemical, and genetic analyses of bronchiolar adenoma and its putative variants

We collected 26 cases of bronchiolar adenoma (BA) and its variants, and performed a comprehensive characterization using a combination of morphological, immunohistochemical, and genetic assessments. Of these 26, 13 were classic bilayered cases, including 10 proximal and 3 distal-type BAs. Of note, we also identified 13 cases that lacked a continuous basal cell layer. In five cases, the adenomas were partially classic bilayered, leaving a single layer of columnar or cuboidal epithelial cells in some areas of the lesion (BA with monolayered cell lesions). In the other eight cases, the glandular or papillary structures were entirely composed of monolayered columnar or cuboidal epithelial cells, which were morphologically identical to the luminal epithelial cells of classic BA (monolayered BA-like lesions). Immunohistochemical analysis revealed thyroid transcription factor 1 expression by ciliated columnar epithelial cells, basal cells, and nonciliated columnar and cuboidal epithelial cells. Basal cells also expressed p40 and p63. Twenty-five cases underwent next-generation sequencing using a 422-cancer-gene panel (GeneseeqPrime). Oncogenic driver mutations were detected in 23 cases, including 13 (52%) with EGFR mutations, 4 (16%) with KRAS G12D/V mutations, 3 (12%) with BRAF V600E mutations, 2 (8%) with ERBB2 exon 20 insertions, and 1 (4%) with a RET fusion. EGFR exon 20 insertions were present in 100% of BAs with monolayered cell lesions, 37.5% of monolayered BA-like lesions, and 8% of classic BA (Fisher's exact test, p = 0.002, false discovery rate = 0.014). Collectively, our study revealed a gradual morphological transition between BA and its variants. The genetic composition of BAs with monolayered structures differed significantly from those of classic BAs or lung adenocarcinoma.

CT Texture Analysis for Differentiating Bronchiolar Adenoma, Adenocarcinoma In Situ, and Minimally Invasive Adenocarcinoma of the Lung

Purpose: This study aimed to investigate the potential of computed tomography (CT) imaging features and texture analysis to distinguish bronchiolar adenoma (BA) from adenocarcinoma in situ (AIS)/minimally invasive adenocarcinoma (MIA).

Materials and Methods: Fifteen patients with BA, 38 patients with AIS, and 36 patients with MIA were included in this study. Clinical data and CT imaging features of the three lesions were evaluated. Texture features were extracted from the thin-section unenhanced CT images using Artificial Intelligence Kit software. Then, multivariate logistic regression analysis based on selected texture features was employed to distinguish BA from AIS/MIA. Receiver operating characteristics curves were performed to determine the diagnostic performance of the features.

Results: By comparison with AIS/MIA, significantly different CT imaging features of BA included nodule type, tumor size, and pseudo-cavitation sign. Among them, pseudo-cavitation sign had a moderate diagnostic value for distinguishing BA and AIS/MIA (AUC: 0.741 and 0.708, respectively). Further, a total of 396 quantitative texture features were extracted. After comparation, the top six texture features showing the most significant difference between BA and AIS or MIA were chosen. The ROC results showed that these key texture features had a high diagnostic value for differentiating BA from AIS or MIA, among which the value of a comprehensive model with six selected texture features was the highest (AUC: 0.977 or 0.976, respectively) for BA and AIS or MIA. These results indicated that texture analyses can effectively improve the efficacy of thin-section unenhanced CT for discriminating BA from AIS/MIA.

Conclusion: CT texture analysis can effectively improve the efficacy of thin-section unenhanced CT for discriminating BA from AIS/MIA, which has a potential clinical value and helps pathologist and clinicians to make diagnostic and therapeutic strategies.

Ciliated muconodular papillary tumor/bronchiolar adenoma of the lung

Ciliated muconodular papillary tumor (CMPT) is an uncommon tumor of the lung, usually detected incidentally in the peripheral lung fields on computed tomography. It is most commonly diagnosed in patients between the sixth and last decades of life. The canonical microscopic feature is a tripartite mixture of ciliated columnar, mucous, and basal cells with papillary architecture. However, studies have shown wide morphological variations in this tumor, such as a lack of ciliated columnar or mucous cells and flat instead of papillary architecture. Hence, a new umbrella term, bronchiolar adenoma (BA), has been proposed to encompass all tumors comprising a uniform layer of basal cells underneath the luminal epithelium displaying bronchiolar differentiation. Recent molecular studies on CMPT/BA discovered a high frequency of driver gene alterations, including mutations in the BRAF, EGFR, AKT1, KRAS, and HRAS genes, as well as ALK gene rearrangements. The tumor follows an indolent clinical course, as no recurrences or metastases have been reported in patients who underwent surgical resection. In this article we review the clinical, radiological, and pathological features, and molecular characteristics of CMPTs/BAs.

Benign tumours of the bronchopulmonary system

The vast majority of tumours arising in the bronchopulmonary system are malignant in nature. Benign tumours of the lung are relatively rare and are often incidental findings during clinical investigations for unrelated conditions. These lesions can arise in the bronchial tree or the pulmonary parenchyma and may be of epithelial, mesenchymal, salivary gland-type or unknown differentiation. Although the spectrum of these lesions is wide, the clinical, pathological and immunohistochemical characteristics of the most relevant will be the subject of this review. In addition, the most important features allowing differentiation from malignant pulmonary neoplasms will be discussed.

Mucinous adenocarcinoma caused by cancerization from a ciliated multinodular papilloma tumor: A case report

Ciliated multinodular papilloma tumor (CMPT), a subtype of proximal bronchiolar adenoma (BA), is a rare mucin‐producing papillary tumor arising in the peripheral lung. The nature of CMPT is so far controversial. The hypothesis that CMPT is a precancerous lesion that can lead to mucinous adenocarcinoma requires further research. A 61‐year‐old man with a ground‐glass opacity (GGO) suspected to be lung adenocarcinoma in the right lower lobe of his lung underwent surgical treatment. Postoperative pathology suggested that the patient had mucinous adenocarcinoma caused by cancerization from CMPT. Targeted next‐generation sequencing (NGS) was utilized to detect driver mutations in tumor DNA. Among the identified mutated genes, there were regrettably no high frequency mutations. This report describes a case of mucinous adenocarcinoma caused by cancerization from CMPT, indicating that CMPT may be a neoplasm rather than a metaplastic process and provides histological evidence for the hypothesis that CMPT is a precancerous lesion of mucinous adenocarcinoma.

Bronchiolar Adenoma Transforming to Invasive Mucinous Adenocarcinoma: A Case Report

Bronchiolar adenoma (BA) is recognized as a neoplasm with benign clinical course. Histologically, BA is characterized by nodular proliferation of the bilayered bronchiolar-type epithelium, including multipartite epithelial cells and a continuous layer of basal cells. Recent reports have revealed the frequent presence of driver gene mutations in BA, suggesting its neoplastic nature. However, it is still debatable whether BA has malignant potential. Herein, we report the first case of BA harboring the same KRAS mutation with the adjacent invasive mucinous adenocarcinoma (IMA). Additionally, the loss of continuity of the basal cell layer in the junctional zone between BA and IMA indicated a malignant transformation from BA to IMA in this particular case.

Clinicopathological characteristic of ciliated muconodular papillary tumour of the lung

AIMS

Ciliated muconodular papillary tumour (CMPT) is a rare tumour characterised by tripartite cellular components of mucinous cells, ciliated columnar cells and basal cells with a predominantly papillary architecture. Its clinicopathological characteristics and treatment methods have not been fully elucidated.

METHODS

Twenty-six patients with CMPT diagnosed and treated in our hospital were retrospectively analysed.

RESULTS

The cohort was composed of 13 males and 13 females, with a mean age of 64.4±5.93 years. The diameter of the primary tumour ranged from 0.3 to 1.4 cm. The lesions appeared as subsolid nodules, ground-glass nodules and cavitary nodules under the CT scan. All the patients underwent surgical treatment and did not receive postoperative adjuvant therapy. All the CMPTs were diagnosed by immunohistochemistry and not by intraoperative frozen sections. Next-generation sequencing detection demonstrated EGFR, KRAS and BRAF mutations and ALK rearrangements in CMPTs. The follow-up duration ranged from 5 to 65 months, and no case of tumour recurrence was observed until the final follow-up.

CONCLUSIONS

The incidence of CMPT is low, and the prognosis is good. Immunohistochemistry is helpful for an accurate diagnosis of CMPT, while intraoperative frozen sections cannot fully guide the surgical method. Sublobectomy may be enough without adjuvant treatment. CMPTs exhibited a relatively high rate of driver gene mutations, while the mutation sites were not consistent with those in lung adenocarcinoma.

AKT1 Mutations in Peripheral Bronchiolar Papilloma: Glandular Papilloma and Mixed Squamous Cell and Glandular Papilloma Is Distinct From Bronchiolar Adenoma

Glandular papilloma (GP) and mixed squamous cell and glandular papilloma (MP) are rare benign pulmonary tumors occurring in the bronchi. Bronchiolar adenoma (BA) was recently characterized as a pulmonary tumor exhibiting alveolar spread. Both GP/MP and BA are composed of a mixture of glandular, ciliated, squamous, and basal cells. We aimed to clarify whether GP/MP and BA represent the same tumor. We evaluated the detailed histologic characteristics of 11 cases involving pulmonary peripheral tumors that exhibited histologic features of GP/MP or BA, and performed genetic analyses using targeted panel sequencing, allele-specific polymerase chain reaction, and digital polymerase chain reaction. Histologically, 4 and 7 tumors were classified as GP/MP and BA, respectively. GP/MP showed endobronchiolar papillary growth with a pseudostratified or stratified epithelium. In contrast, 5 BAs showed a predominant flat structure with a bilayered or pseudostratified epithelium, whereas 2 BAs showed a GP/MP-like papillary architecture. The mean epithelial thickness in each tumor was significantly larger in GP/MPs and BAs with a GP/MP-like morphology (103 to 242 μm) than in flat-predominant BA (23 to 47 μm, P=0.0010). AKT1 E17K mutations were detected in all GP/MPs and BAs with GP/MP-like morphology but were absent in the 5 flat-predominant BAs. AKT1 mutations were always concurrent with BRAF or HRAS mutations, and the variant allele frequency or percentage of mutant copies of AKT1 mutations was equal to those of BRAF or HRAS mutations. GP/MPs are characterized by AKT1 mutations concurrent with BRAF or HRAS mutations. Peribronchiolar papillary tumors with AKT1 mutations may also be classified as GP/MP.

Ciliated Muconodular Papillary Tumors of the Lung: Distinct Molecular Features of an Insidious Tumor

Introduction

Ciliated muconodular papillary tumors (CMPTs) are rare special peripheral pulmonary nodule composed of different cell proportions, characterized by papillary structures and significant alveolar mucus. Because of their rarity, underrecognized processes, the full range clinical course and histogenesis of CMPTs remains uncertain.

Methods

Molecular features of 5 CMPTs cases (one case with mucinous adenocarcinoma simultaneously) were observed by whole exon gene detection. The histological features of CMPTs and the development trends of three major constituent cells were studied by immunohistochemistry and PCR.

Results

NGS revealed 77 gene mutations in the patient's tumor tissue and 31 mutations in the border tissue. TMB of CMPT tends to TMB of cancer tissues, and both are higher than normal tissues, CMPT share the same phylogenetic tree with cancer tissues. Moreover, PDL1, B7H3, and B7H4 were overexpressed in high columnar cells and eosinophilic ciliated cells of CMPT, tends to cancer tissues, while LAG3 and siglec15 were not found in CMPT.

Conclusion

The high prevalence of driver gene mutations in CMPTs, similar TMB and phylogenetic tree with cancer tissues indicate their malignant potential. Distinct molecular and immune check point features of each component support the notion that ciliated columnar cells in CMPT are insidious with immune escape.

First case of bronchiolar adenoma lined purely by mucinous luminal cells with molecular analysis: A case report

RATIONALE

Bronchiolar adenoma (BA) is a newly designated rare entity of the lung, including both the currently designated ciliated muconodular papillary tumor (CMPT) and so-called non-classic CMPT. The most prominent histological feature of BAs is the bilayered cell structures composed of the continuous basal cell layer and the luminal layer which consists of different proportion of mucinous cells, ciliated cells, Clara cells and/or type II pneumocytes. BA purely covered by mucinous cells without other components in the luminal layer has never been reported.

PATIENT CONCERNS

An 82-year-old female patient was detected a 0.8 cm ground glass nodule in the left lower lobe of the lung.

DIAGNOSES

The serum levels of tumor markers were normal.

INTERVENTIONS

The patient underwent a segmentectomy of the left lower lobe.

OUTCOMES

The postoperative pathological diagnosis was BA. Molecular analysis revealed that the tumor harbored ALK rearrangement and BRAF mutations simultaneously. There was no recurrence in 17 months of follow-up.

LESSONS

BA can be lined only by mucinous cells, without any cuboidal and/or ciliated cells in the surface layer. This sets a dangerous pitfall in differentiation diagnosis with invasive mucinous adenocarcinoma especially during intraoperative frozen pathological diagnosis.

Bronchiolar adenoma with diffuse pulmonary nodules: a extremely rare case report and review of literature

Background

Bronchiolar adenoma(BA) is a recently recognized, rare tumor of the bronchioles. It can be divided into proximal and distal types according to the proportion of mucinous and ciliated cells on the luminal surface. BA is often misdiagnosed because it has similar ultrasonographic, gross and histological presentations as other diseases. Here, we report a rare case of BA characterized by many fused nodules.

Case presentation

A 68-year-old woman attended the Tianjin Taida Hospital surgical Clinic mainly because of “intermittent cough for >1 month”. Chest computed tomography (CT) showed multiple solid nodules in the upper and lower left lung. The nodules had irregular outlines, with a maximum diameter of 65 mm. A double needle lung biopsy specimen was removed guided by ultrasound under local anesthesia. Histologically, the biopsy specimen was finally diagnosed as the distal type of BA.

Conclusion

BA with diffuse pulmonary nodules is rare. Diagnosis of BA needs comprehensive analysis of imaging, gross specimen analysis, histopathology, and immunohistochemical staining to make a correct diagnosis and avoid misdiagnosis. There are few studies on prognosis, which needs close follow-up and more data accumulation.

Pulmonary peripheral glandular papilloma and mixed squamous cell and glandular papilloma frequently harbour the BRAF V600E mutation

AIMS

Pulmonary peripheral glandular papilloma (GP) and mixed squamous cell and glandular papilloma (MP) have very similar histological features to pulmonary ciliated muconodular papillary tumour (CMPT)/bronchiolar adenoma (BA). The underlying genetic relationships between GP/MP and CMPT/BA have rarely been characterised. We aimed to reveal the relationship between them.

METHODS AND RESULTS

We performed a clinicopathological review and next-generation sequencing (NGS) study of two GPs and five MPs. Histologically, GPs/MPs showed similar cellular and architectural features to CMPTs/BAs, such as bilayered epithelium, bronchiole-associated lesions and skipping (discontinuous) growth pattern. One MP showed partial and inconspicuous endobronchiolar growth and more glandular structures, which was very similar to the appearance of CMPT/BA. BRAF V600E mutation was detected in four papillomas (57.1%, one GP and three MPs).

CONCLUSIONS

Overlapping morphological features and comparable mutation profiles support that peripheral GPs/MPs and CMPTs/BAs are on the same disease spectrum. We propose expanding the concept of CMPT/BA and including GP and MP in the CMPT/BA family.

Ciliated Muconodular Papillary Tumor of the Lung: Thin-Section CT Findings of 16 Cases

OBJECTIVE. The purpose of this article was to assess thin-section CT features of ciliated muconodular papillary tumors (CMPTs) of the lung and correlations between radiologic and pathologic findings. MATERIALS AND METHODS. Thin-section CT findings of 16 patients (10 men and six women; mean age, 70.7 years) with surgically resected CMPTs were retrospectively analyzed. Size, location, and internal characteristics of the tumors were evaluated. The amount of mucin in the tumors was assessed histopathologically and compared with CT findings. Tumor growth speed was calculated on the basis of size changes on thin-section CT. RESULTS. In all 16 patients, tumors were detected as a solitary pulmonary nodule. Thirteen tumors (81.3%) were located in the lower lobes, and 10 (62.5%) were adjacent to the pleura. Mean maximal diameter of the tumors was 9.1 mm (range, 6-14 mm). One tumor (6.3%) presented as a pure ground-glass nodule (GGN), seven (43.8%) as dense GGNs, and eight (50.0%) as solid nodules. Pathologically, the pure GGN and five of seven dense GGNs had a large amount of mucin, whereas seven of eight solid nodules had an intermediate or small amount of mucin. The mean annual tumor growth rate (in diameter) was 0.49 mm/y. CONCLUSION. CMPTs appear as solitary, small, and peripheral pulmonary nodules with very slow growth rates. CMPTs appearing as pure GGNs and dense GGNs tend to contain more mucin than CMPTs appearing as solid nodules.

[A Case of Typical Ciliated Muconodular Papillary Tumor of the Lung: A Clinicopathological Analysis]

BACKGROUND

The pathogenesis of a ciliated muconodular papillary tumor (CMPT) of the lung is extremely rare which is difficult to distinguish from other lung lesions and it is easy to cause misdiagnosis and missed diagnosis. By collecting CMPT data, its clinical and pathological features can provide medical treatment ideas for the majority of medical workers and reduce medical errors.

METHODS

The clinical data, pathological features, immunophenotype of a typical CMPT patient and related literature were analyzed.

RESULTS

The chest computed tomography (CT) showed there was a mixed density nodule in the right lower lung near the pleura with a diameter of about 9 mm. We performed a wedge resection on the patient. The pathological results showed that the nodule was composed of proliferated ciliated cells, mucous cells, and basal-like cells. The ciliated cells were lined on the surface of papillary structures. The basal-like cells were located in the outer layer, while the mucous cells were located between the two. The cell atypia was not obvious. Immunohistochemistry: epithelial cells CEA (+), CK7 (+), CA125 (+), weakly positive for TTF-1, CK20 (-), Ki67 (1%+), CK5/6 (+), and basal cells P63 (+).

CONCLUSIONS

CMPT is a rare pulmonary neoplasm. There is no definite conclusion about its biologic nature, but most experts prefer a benign to a malignant tumor. CMPT can show many malignant tumor signs on imaging and is often mistaken for lung adenocarcinoma. According to its typical histopathological characteristics and immunohistochemical phenotype, it can be differentiated from other pulmonary diseases. Whether gene mutation is the driving factor is still unknown. Surgical resection for the tumor reveals a good prognosis.

Ciliated muconodular papillary tumor of the lung presenting with polymyalgia rheumatica-like symptoms: a case report

Ciliated muconodular papillary tumors (CMPTs) of the lung have been recently characterized as low-grade malignant tumors and may be indistinguishable from adenocarcinoma in situ (AIS) because they are both abundant in mucous and spread along the alveolar walls. Herein, we report a case of CMPT with polymyalgia rheumatica (PMR)-like symptoms, which resolved after resection. After the surgery, antinuclear antibody tests were performed, but no abnormalities were noted. Furthermore, the lung tumor could not be distinguished from AIS, as revealed by a pathological examination. This case demonstrates two key points: the paraneoplastic symptoms of CMPT can indicate PMR, and it is difficult to diagnose peripheral lung tumors as CMPT unless there is a completely resected specimen available. The possibility exists that an increased number of older patients will be diagnosed with CMPT because of the increasing frequency of computed tomography performed in this population. Therefore, it is important for clinicians to obtain completely resected specimens to ensure accurate diagnosis and management of CMPT.

Epithelial cell plasticity defines heterogeneity in lung cancer

Lung cancer is the leading cause of cancer death for both men and women and accounts for almost 18.4% of all deaths due to cancer worldwide, with the global incidence increasing by approximately 0.5% per year. Lung cancer is regarded as a devastating type of cancer owing to its high prevalence, reduction in the health-related quality of life, frequently delayed diagnosis, low response rate, high toxicity, and resistance to available therapeutic options. The highly heterogeneous nature of this cancer with a proximal-to-distal distribution throughout the respiratory tract dramatically affects its diagnostic and therapeutic management. The diverse composition and plasticity of lung epithelial cells across the respiratory tract are regarded as significant factors underlying lung cancer heterogeneity. Therefore, definitions of the cells of origin for different types of lung cancer are urgently needed to understand lung cancer biology and to achieve early diagnosis and develop cell-targeted therapies. In the present review, we will discuss the current understanding of the cellular and molecular alterations in distinct lung epithelial cells that result in each type of lung cancer.

Ciliated muconodular papillary tumor of the lung: report of two cases and review of the literature

Ciliated muconodular papillary tumor (CMPT) is a peripheral non-endobronchial lung nodule, consisting of ciliated columnar cells and goblet cells with basaloid cell proliferation. Only about 50 cases confirmed by surgery have been reported in English literature worldwide. We present two surgical cases of CMPT in this report. Two patients presented with abnormal computed tomography findings but no obvious symptoms. The first patient's intraoperative frozen examination was unable to distinguish benignity from malignancy, and he received lobectomy. The other patient's intraoperative frozen examination indicated adenocarcinoma, but she received wedge resection for her refusal to lobectomy. The two patients' postoperative pathological analysis finally confirmed the diagnosis of CMPT. We believe that our cases may be essential for pathologists and surgeons to improve their understanding.

Clinicopathological features and prognosis of ciliated muconodular papillary tumor

BACKGROUNDS

The pulmonary ciliated muconodular papillary tumor (CMPT) is a very rare tumor with only several case reports in published literatures, and its clinicopathological features, standard treatment methods and prognosis has not been well defined.

METHODS

Two cases of CMPT diagnosed and treated in our hospital and 39 cases reported in the published literature were analyzed retrospectively.

RESULTS

The cohort of 41 CMPT patients comprised of 20 males and 21 females, aged 9-84 years. The diameter of the primary tumor was 0.3-4.5 cm. Most of these lesions were subsolid nodules, as observed on computed tomography and easily misdiagnosed as early lung adenocarcinoma. Tumors of 26 patients were stained by immunohistochemistry method, which revealed that CK7, CEA, and TTF-1 were positive and CK20 was negative in most patients. The results of gene alternation demonstrated mutations in EGFR, KRAS, and BRAF and ALK rearrangements in CMPT. All the patients underwent surgical treatment and did not receive postoperative adjuvant therapy. The follow-up duration was 0-120 months, and no case of tumor recurrence was found until the final follow-up.

CONCLUSIONS

The incidence of CMPT was low and rate of image misdiagnosis high. Immunohistochemistry is helpful for accurate diagnosis of CMPT. Sub-lobectomy may be proper and adjuvant treatment should be avoided since the disease is now prone to benign lesions. Furthermore, since the biological behavior of this tumor is not yet fully elucidated, additional case data are essential for accurate conclusions.

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

We have identified 25 lesions involving alveolar lung parenchyma characterized by nodular proliferation of bland bilayered bronchiolar-type epithelium containing a continuous layer of basal cells. These lesions shared some histologic features with the recently described entity of ciliated muconodular papillary tumor (CMPT); however, the majority did not fit all diagnostic criteria in that they exhibited only focal or absent papillary architecture, and they had variable number of ciliated and mucinous cells, with some lesions entirely lacking 1 or both of these components. The morphologic and immunohistochemical features ranged from those resembling proximal bronchioles (proximal-type: moderate to abundant mucinous and ciliated cells; negative or weak TTF1 in luminal cells; n=8) to those resembling respiratory bronchioles (distal-type: scant or absent mucinous and ciliated cells; positive TTF1 in luminal cells; n=17). The hallmark of all lesions was a continuous layer of basal cells (p40 and CK5/6-positive). We provisionally designated these lesions as bronchiolar adenomas (BAs) and analyzed their clinicopathologic and molecular features. All BAs were discrete, sharply circumscribed lesions with a median size of 0.5 cm (range, 0.2 to 2.0 cm). Most lesions were either entirely flat (n=14) or contained focal papillary architecture (n=7); only 4 lesions, all proximal-type, were predominantly papillary, fitting the classic description of CMPT. Notably, of 9 lesions submitted for frozen section evaluation, 7 were diagnosed as adenocarcinoma. No postsurgical recurrences were observed for any lesions (median follow-up, 11 mo). Twenty-one BAs underwent next-generation sequencing and/or immunohistochemistry for BRAF V600E, revealing mutation profiles similar to those previously described for CMPTs, including BRAF V600E mutations (n=8, 38%), unusual EGFR exon 19 deletions (n=2, 10%), EGFR exon 20 insertions (n=2, 10%), KRAS mutations (n=5, 24%), and HRAS mutations (n=1, 5%). The mutation profiles were similar in proximal-type and distal-type lesions. In conclusion, we describe a family of putatively benign clonal proliferations with a spectrum of morphology recapitulating various levels of the bronchiolar tree, of which only a minor subset fits the classic description of CMPT. Comparable mutation profiles and partially overlapping morphologic features across the spectrum of these lesions support their nosological relationship. We propose designating this entire family of lesions as BAs, and that lesions currently designated CMPTs represent a subgroup of this family.

Motile ciliogenesis and the mitotic prism

Motile cilia of epithelial multiciliated cells transport vital fluids along organ lumens to promote essential respiratory, reproductive and brain functions. Progenitors of multiciliated cells undergo massive and coordinated organelle remodelling during their differentiation for subsequent motile ciliogenesis. Defects in multiciliated cell differentiation lead to severe cilia-related diseases by perturbing cilia-based flows. Recent work designated the machinery of mitosis as the orchestrator of the orderly progression of differentiation associated with multiple motile cilia formation. By examining the events leading to motile ciliogenesis with a methodological prism of mitosis, we contextualise and discuss the recent findings to broaden the spectrum of questions related to the differentiation of mammalian multiciliated cells.

Solitary peribronchiolar metaplasia showing a sub-solid nodule on computed tomography

Recent advances in radiographic imaging and thoracic surgery have facilitated surgery for small lung tumors by eliminating the need for pathological diagnosis. To date, we have experienced two cases of small lung tumors that were surgically resected without pathological diagnosis as malignant. Computed tomography (CT) revealed sub-solid nodules in the peripheral lung. After tumor resection, both tumors were pathologically diagnosed as peribronchiolar metaplasia. To the best of our knowledge, solitary peribronchiolar metaplasia showing a sub-solid nodule on CT imaging has not previously been reported.

A surgical case of ciliated muconodular papillary tumor

Ciliated muconodular papillary tumor (CMPT) is a rare type of pulmonary tumor with mucoid features. Only a few cases confirmed by surgery have been reported worldwide. We report a case of CMPT following sublobectomy, with no recurrence detected in 10 months of follow-up. The accumulation of similar cases is essential for pathologists and surgeons to improve their understanding of such tumors.

Ciliated Muconodular Papillary Tumors of the Lung

Ciliated muconodular papillary tumor is a rare tumor of the lung with 38 cases reported to date in the English literature. It is typically found incidentally in older adults (average age, 67 years) as a small, peripheral, ground glass opacity or nodule on computed tomography. Microscopically, the tumor is composed of a mixture of ciliated columnar, mucous, and basal cells in a variety of architectural patterns including glandular, papillary, lepidic, and micropapillary growth patterns. Recently, studies have shown the tumor has several associated gene alterations, supporting that the lesion is indeed neoplastic. The tumor seemingly follows an indolent clinical course, as there have been no reported recurrences or metastases. In this article, we review the clinical, radiographic, pathologic, and molecular findings of ciliated muconodular papillary tumors. Diagnostic pitfalls and the diagnostic considerations are discussed.

So-called "non-classic" ciliated muconodular papillary tumors: a comprehensive comparison of the clinicopathological and molecular features with classic ciliated muconodular papillary tumors

Ciliated muconodular papillary tumors (CMPTs) are characterized by tripartite cellular components of ciliated columnar cells, mucinous cells, and basal cells with predominantly papillary architecture. Some peripheral lung nodules may not demonstrate papillary architecture and tripartite cells that show bronchiolar differentiation; these nodules are termed "CMPTs with non-classic morphology" by some authors. To validate the rationality of "non-classic" CMPTs and to analyze the clinicopathological features of CMPTs, we enrolled 21 cases of lung nodules, comprising classic CMPTs (n = 11) and so-called non-classic CMPTs (n = 10). The status of driver mutations, including those in EGFR, BRAF, ALK, and KRAS, was examined by molecular tests. Clinical and radiological follow-up was performed (3-27 months). Cilia as well as the mucinous and papillary components are usually present throughout classic CMPTs but may be absent in their non-classic counterparts. However, both entities present a bi-layer architecture with evidence of bronchiolar differentiation. Driver mutations involved the BRAF (n = 6), EGFR (n = 1) and ALK (n = 1), were identified in 8 of 11 (73%) classic CMPTs, whereas driver mutations, comprising BRAF (n = 2), EGFR (n = 1) and KRAS (n = 1), were identified in 4 of 10 (40%) non-classic lesions. Since it contains the largest series of Chinese patients with CMPTs, this study may expand the morphologic and molecular spectrum of CMPTs: a hallmark of CMPTs is bi-layer architecture with a continuous basal layer that can harbor high-frequency driver mutations. Recognition of the non-classic morphology of CMPTs may be helpful to avoid misdiagnosis and unnecessary treatment.