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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.

The pathologist is frequently involved in the diagnostic approach to the patient with suspected sarcoidosis. Although the histologic diagnosis is generally not difficult, atypical and underrecognized features may occasionally occur and may result in diagnostic problems. The authors review the histology of pulmonary sarcoidosis, focusing particularly on these unusual problematic findings.

We report a rare case of malignant pleural mesotheliomapresentingclinically with pneumotho ax and histologically with an exclusiveintrapulmonary lepidic growth. Neither intrathoracic nodules norpleural thickening were found. The patient subsequently experiencedacute abdominal painwith peritonitis and intestinal occlusion byperitoneal mesothelioma. The morphologic clues leading to the correct diagnosis of mesothelioma with prominent intrapulmonary growth are briefly discussed.

Primary renal lymphomas are very rare, and primary kidney-limited lymphomas with cystic presentation have never been described before. This study reports a case of diffuse large B-cell lymphoma associated with chronic inflammation occurring in a renal pseudocyst: an infrequent neoplasm with an unusual and subtle clinical presentation.

Pulmonary mucin-producing adenocarcinomas may be indistinguishable on conventional histology from a metastasis, as thyroid transcription factor-1 (TTF-1) expression often is lacking and KRAS mutations are widely present even in extrapulmonary sites. Few data have been reported on the diagnostic role of napsin-A and epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK) gene alterations in this challenging differential diagnosis. Seventy-seven surgically resected cases, including 53 primary and 24 metastatic tumors from different sites, were evaluated for napsin-A, TTF-1, and ALK by immunohistochemistry and for EGFR mutations by direct sequencing. Overall, napsin-A expression in primary lung mucin-producing adenocarcinomas was 36% (8% mucinous, 17% colloid, 87.5% solid, and 100% signet ring cell) and TTF-1 expression reached an overall figure of 42% (12.5% mucinous, 33% colloid, 87.5% solid, and 100% signet ring cell). Metastatic mucinous adenocarcinomas did not react with napsin-A or with TTF-1. All primary and metastatic tumors lacked EGFR mutations, while a single case of signet ring cell lung adenocarcinoma showed ALK expression and rearrangement at fluorescent in situ hybridization analysis. Napsin-A has a lower sensitivity compared with TTF-1 in primary mucin-producing adenocarcinomas of the lung. However, both antibodies have an absolute specificity, being always negative in metastatic mucinous adenocarcinomas. EGFR mutations and ALK translocation or expression are exceedingly rare in mucin-producing adenocarcinomas of the lung, resulting unnecessary as diagnostic tool in this setting.

Morphology still remains the cornerstone in lung cancer classification and cytology and small biopsy samples should be interpreted by morphology, whenever feasible, according to shared and widely agreed-upon diagnostic schemes. However, as novel therapy strategies are being offered on the basis of the diverse tumor characteristics, pathologists are now challenged by the need to offer clinicians more detailed typing of non–small cell lung cancer, not otherwise specified (NSCLC-NOS), especially when dealing with limited diagnostic material or poorly differentiated tumors. Close integration of morphology, immunohistochemistry, and clinical data is highly warranted according to a multidisciplinary approach to limit the category of NSCLC-NOS as much as possible or exclude unsuspected metastases, so rendering more definite and clinically useful diagnoses. Among the many proposed immunohistochemical markers, which as a whole are more practical and diagnostically useful than cumbersome and expensive molecular assays, a 2-hit model including thyroid transcription factor-1 (TTF-1) and p40 (the latter more specific for squamous differentiation than p63) seems to be the most effective to basically highlight adenocarcinoma (positivity for TTF-1 regardless of p63) and squamous (always strongly and diffusely positive for p40 or p63 and negative for TTF-1) differentiation. This minimalist 2-hit diagnostic approach paves the way to novel perspectives in clinical trials on lung cancer, and it is also in keeping with the need of strategically preserving diagnostic material for molecular assays that are essential for personalizing therapies.

The authors describe a case of multifocal perivascular epithelioid cell tumor (PEComa) arising in the pelvis of a 39-year-old woman affected by tuberous sclerosis. The tumor presented in the form of multiple fascicular, focally cystic nodules involving the uterine corpus, both ovaries, and the omentum. Microscopically, the nodules were composed of foci of adenomyosis and endometriosis (with focal atypical complex hyperplasia) associated with a stromal spindle cell population immunoreactive for HMB-45, smooth muscle actin, and estrogen and progesterone receptors. We interpret these foci as the result of a widespread proliferation of perivascular epithelioid cells (PEC). Because of the diffuse quality of the process, the designation of PEComatosis seems warranted.

We describe an alveolar adenoma of the lung with 3 previously unreported findings, which expand both the clinical and the morphologic spectrum of this rare tumor: presentation as a cystic nodule, foci of mature adipocytes, and S-100 positivity of the mesenchymal cells. Furthermore, using a laser capture microdissection technique under microscope visualization, we analyzed multiple chromosomal loci in both the epithelial and mesenchymal components of the lesion, showing microsatellite alterations and loss of heterozygosity in the former but not in the latter.