Mucinous Adenomyomatous Pulmonary Hamartoma: Clinicopathologic, Immunohistochemical, and Molecular Features of 6 Cases.

Pulmonary hamartoma (PH) may show various combinations of mesenchymal tissues with entrapment of respiratory epithelium. An uncommon variant of PH prevalently consisting of smooth muscle with mucinous proliferation has been reported in literature under several definitions as sporadic reports. We collected a series of 6 leiomyomatous PH associated with mucinous growth from consultation files (3 cases) and multicentric revision of archival files among 128 consecutive surgically resected PH. The lesions have a prevalence for male gender (5:1) and lower lobes (5:1), with a mean age at diagnosis of 61 years. All cases were incidentally disclosed in asymptomatic patients and had an indolent behavior. At histology, 2 cases consisted uniquely of smooth muscle and 4 also showed mature adipose tissue. The mucinous proliferation consisted of a monotonous growth of columnar cells lacking p63-positive basal cells and expressing pan-CKs, MUC5A, and CK7, but negative with TTF-1, napsin, MUC1, MUC2, MUC6, CK20, and CDX2. Smooth muscle was negative with hormonal receptors. Molecular analysis using a multiplex gene panel did not reveal gene mutations, while ALK, BRAF, and ROS1 were negative. In conclusion, we describe a small series of uncommon PH with prevalent leiomyomatous mesenchymal component associated with a mucinous growth (mucinous adenomyomatous hamartoma). Despite the lack of basal cells coating mucinous proliferation and irregular architecture, the favorable outcome and lack of molecular alterations most likely lay for a benign/low-grade tumor. Pathologists should be aware of this unusual occurrence to prevent a diagnosis of overt malignancy, particularly in frozen section, small biopsy, and cytology.

Diffuse idiopathic pulmonary neuroendocrine cell hyperplasia syndrome.

The term diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH) may be used to describe a clinico-pathological syndrome, as well as an incidental finding on histological examination, although there are obvious differences between these two scenarios. According to the World Health Organization, the definition of DIPNECH is purely histological. However, DIPNECH encompasses symptomatic patients with airway disease, as well as asymptomatic patients with neuroendocrine cell hyperplasia associated with multiple tumourlets/carcinoid tumours. DIPNECH is also considered a pre-neoplastic lesion in the spectrum of pulmonary neuroendocrine tumours, because it is commonly found in patients with peripheral carcinoid tumours.In this review, we summarise clinical, physiological, radiological and histological features of DIPNECH and critically discuss recently proposed diagnostic criteria. In addition, we propose that the term "DIPNECH syndrome" be used to indicate a sufficiently distinct patient subgroup characterised by respiratory symptoms, airflow obstruction, mosaic attenuation with air trapping on chest imaging and constrictive obliterative bronchiolitis, often with nodular proliferation of neuroendocrine cells with/without tumourlets/carcinoid tumours on histology. Surgical lung biopsy is the diagnostic gold standard. However, in the appropriate clinical and radiological setting, transbronchial lung biopsy may also allow a confident diagnosis of DIPNECH syndrome.

Squamous Cell Carcinoma "Transformation" Concurrent with Secondary T790M Mutation in Resistant EGFR-Mutated Adenocarcinomas.

The authors report two cases of epidermal growth factor receptor gene (EGFR)-mutant stage IV lung adenocarcinomas developing immunohistochemically proven squamous cell carcinoma (SCC) "transformation" concurrently with T790M EGFR mutation, leading to acquired resistance to EGFR inhibitors. Moreover, the histologic change of EGFR-mutant lung adenocarcinoma into SCC has been recently reported in literature. The histological transformation to SCC appears as a novel mechanism of acquired EGFR TKI resistance in EGFR-mutated adenocarcinomas and it may be challenging for treatment.

Rhabdomyoma of the Lip: A Case Report With Review of the Literature.

Rhabdomyoma (RM) is a rare benign mesenchymal tumor associated with skeletal muscle differentiation. We report a case of adult-type RM occurring in the lower lip of a 48-year-old man, clinically suspicious for squamous cell carcinoma. Only 3 cases of adult-type RM have been described in the literature in this anatomical site. The histologic differential diagnoses with other lesions are presented, with emphasis on immunohistochemical aspects.

Classification of different patterns of pulmonary adenocarcinomas.

The epidemic increase of adenocarcinoma histology accounting for more than 50% of primary lung malignancies and the advent of effective molecular targeted-therapies against specific gene alterations characterizing this tumor type have led to the reconsideration of the pathologic classification of lung cancer. The new 2015 WHO classification provided the basis for a multidisciplinary approach emphasizing the close correlation among clinical, radiologic and molecular characteristics and histopathologic pattern of lung adenocarcinoma. The terms 'bronchioloalveolar carcinoma' and 'mixed adenocarcinoma' have been eliminated, introducing the concepts of 'adenocarcinoma in situ', 'minimally invasive adenocarcinoma' and the use of descriptive predominant patterns in invasive adenocarcinomas (lepidic, acinar, papillary, solid and micropapillary patterns). 'Invasive mucinous adenocarcinoma' is the new definition for mucinous bronchioloalveolar carcinoma, and some variants of invasive adenocarcinoma have been included, namely colloid, enteric and fetal-type adenocarcinomas. A concise update of the immunomorphologic, radiological and molecular characteristics of the different histologic patterns of lung adenocarcinoma is reported here.