Three cases of an unusual neoplasm of the lung appeared as solitary, peripheral pulmonary nodules in asymptomatic patients. These well-circumscribed neoplasms were composed of distinctive papillae covered by uniform cuboidal to columnar cells; more solid areas often were present. Ciliated cells, epithelial mucin, and necrosis were not observed, and mitotic activity was absent. Terminal tight junctions and microvilli were present in the two cases studied ultrastructurally. One specimen contained lamellar bodies and apical cytoplasmic dense bodies. Another case stained positively for a Clara cell-specific antigen, although surfactant apoprotein was not detected by immunostaining in the three cases. All patients have been free of disease (at 11 to 108 months). Papillary adenoma is an uncommon, apparently benign, and morphologically distinctive neoplasm. The immunohistochemical and ultrastructural findings hint at an origin from type II pneumocytes or Clara cells.

Papillary adenoma of the lung. Histological and ultrastructural findings in two cases. Acta Pathol Jpn. 1992 Jan;42(1):56-61.

Two cases of papillary adenoma of the lung are presented along with results of histological and ultrastructural examinations. The tumors were encountered in two asymptomatic patients in a mass-survey chest X-ray examination. The chest X-ray films showed the tumors as well demarcated small lesions. Histologically, both tumors arose in the bronchioles and consisted of cuboidal cells resembling type II pneumocytes showing papillary growth with accompanying edematous connective tissue. Several tumor cells each possessed a large eosinophilic intranuclear inclusion. In case 1, ciliated cells and Clara-like cells were also present in the tumor. Ultrastructurally, most of the tumor cells had various numbers of lamellar bodies in their cytoplasm, indicative of type II pneumocytes, and some of case 1 showed features of Clara cells and ciliated cells. The intranuclear inclusions appeared as aggregates of tubular structures or had lamellar body-like features. These findings are identical to those of papillary adenoma arising from the bronchiole.

Papillary adenoma of the lung with lamellar and electron dense granules. An ultrastructural study.Cancer. 1982 Dec 15;50(12):2839-44.

An unusual papillary adenoma in the periphery of the lung was resected in a 25-year-old woman. Examination of the tumor showed a noninfiltrating cellular neoplasms consisting of cuboidal to columnar epithelial cells with eosinophilic granular cytoplasm and without nuclear atypia. Ultrastructurally the tumor cells had microvilli, infrequent cell junctions, and cytoplasmic dense granules and whorled lamellar membrane membrane inclusions. These findings suggest that this benign pulmonary neoplasm has morphologic characteristics consistent with a Clara Cell and alveolar type II pneumocyte differentiation. Although tumors of similar types can be experimentally induced in mice, and the light microscopic features of similar human neoplasms have been described, this is the first report of the ultrastructural characteristics of a benign human lung tumor with morphologic features resembling Clara cell and alveolar type II pneumocytes.

Papillary adenoma of the lung-two cases report.Zhonghua Jie He He Hu Xi Za Zhi. 1992 Oct;15(5):296-7, 320.

Two rare cases of papillary adenoma of the lung were reported. Histologically, the tumor cells had noninfiltrating papillary growth, cuboidal to columnar with eosinophilc granular cytoplasm and without nuclear atypia. Ultrastructurally, the tumor cells had cytoplasmic osmiophilic lamellar bodies. This benign papillary adenoma of the lung has morphologic characteristics consistent with aveolar type II pneumocyte differentiation.

Papillary adenoma of type 2 pneumocytes.Am J Surg Pathol. 1986 Feb;10(2):134-9.

A case of papillary adenoma of type 2 pneumocytes is reported. A 57-year-old man had an unusual coin lesion in the periphery of the right lung without any symptoms. When detected in a mass survey examination, it was approximately 1.5 cm in diameter, well circumscribed, and located in S4, involving the sixth-order bronchus of B4. Light-microscopic examination revealed cuboidal tumor cells arranged in a papillary pattern. Ultrastructurally, the cells had characteristic osmiophilic lamellar bodies. By immunoperoxidase staining, the tumor cells were shown to have intracytoplasmic surfactant apoproteins. The postoperative course was uneventful, and there is no evidence of disease 8 years later.

Papillary adenoma of type II pneumocytes might have malignant potential.Virchows Arch. 1996 Jun;428(3):195-200

Papillary adenoma of type II pneumocytes is a rare tumour. It is considered to be a benign neoplasm and is derived from immature cells in the bronchioloalveolar epithelium, however, its biological nature has not been elucidated. We report a case of an adenomatous tumour; a papillary adenoma of type II pneumocytes, which we regard as possessing malignant potential. Light microscopically, as well circumscribed, papillary tumour of predominantly cuboidal cells resembling type II pneumocytes was found, but Clara type and ciliated cells were also present. Immunohistochemically, the tumour cells reacted positively with antibodies to surfactant apoproteins (A, B), carcinoembryonic antigen, cytochrome P-450 1A1-2 and 2B1-2. Ultrastructurally, many osmiophilic lamellar bodies and electron-dense granules were demonstrated. Semi-serial sections revealed signs of transbronchial dissemination and vascular invasion. Morphometry using 12-dimensional cluster analysis disclosed features of the tumour cells which resembled those of pneumocyte type II adenocarcinoma. These findings suggest that the present case has some malignant characteristics and originates from immature bronchiolar or alveolar cells, with a potential to develop into both type II pneumocyte and Clara cell type adenocarcinomas.

Peripheral papillary tumor of type-II pneumocytes: a rare neoplasm of undetermined malignant potential.Virchows Arch. 2000 Mar;436(3):289-95.

Peripheral papillary adenomas of the lung are uncommon neoplasms (only ten cases have been described so far in the English literature) composed predominantly of type-II pneumocytes and generally considered benign. We describe here two additional cases of this lung tumor. In both cases histological examination revealed an encapsulated papillary neoplasm with invasion of the capsule and, in one case, invasion of the adjacent alveoli and visceral pleura too. The proliferative index (Ki67) was less than 2% and the epithelial cells were positive for cytokeratins, surfactant apoproteins (SP), and nuclear thyroid transcription factor-1 (TTF- 1). Ultrastructurally, the epithelial cells showed the characteristic surface microvilli and cytoplasmic lamellar inclusions of type-II cells. Review of the literature has revealed two other cases of peripheral papillary adenoma of type-II pneumocytes with infiltrative features. Thus, we propose replacing the term peripheral papillary adenoma with peripheral papillary tumor of undetermined malignant potential.

Encapsulated type II pneumocyte adenoma: a case report and review of the literature.Respiration. 1993;60(6):373-7.

An unusual benign lung neoplasm, a papillary adenoma of type II pneumocytes, was resected from a 26-year-old man who showed no clinical symptoms. The tumor was 2.0 cm in diameter and was localized in the subpleural region of S7 of the right lung; the cut surface showed a spherical medullary mass encapsulated by a thin layer of connective tissue. Histologically, there were cuboidal to columnar epithelial cells with a little nuclear atypia showing a monotonous papillary pattern with a delicate stroma in most parts of the tumor. There was neither capsular invasion nor metastasis of tumor cells. Nuclear DNA analysis of the tumor cells showed a diploid pattern and a low S-phase fraction. The immunohistochemical study revealed that most tumor cells contained a large amount of surfactant apoprotein in the cytoplasm. Osmiophilic lamellar bodies characteristic of type II pneumocytes were frequently found by electron microscopy. These findings indicate that this was a benign adenoma of the lung arising from type II pneumocytes.

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