Unusual tumours of the lung and pleura
Authors: Gibbs A R 
Published: September 2007

Abstract:  There are about a hundred histological types of tumour which involve the lung and pleura ranging from inflammatory pseudotumours to highly aggressive malignancies such as small cell carcinoma (Brambilla et al. 2001). The commonly used term lung cancer encompasses only a few histological types – squamous cell carcinoma, adenocarcinoma, small cell carcinoma and large cell carcinoma – but these account for about 95% of lung tumours. The clinical presentation of these tumours reflects their location and aggressiveness and are not specific to any one tumour. Tumours affecting large airways tend to present with obstructive symptoms namely cough, shortness of breath, haemoptysis, and wheeze whereas peripheral tumours are associated with pleural effusion and chest pain. Tumours such as small cell carcinoma mat present with metastases.

In this presentation it is not possible to describe every unusual tumour of the lung and pleura so a select few will be presented.

Carcinomas with pleomorphic, sarcomatoid or sarcomatous elements These are rare tumours which are poorly differentiated non‐small cell carcinomas that contain a component of sarcoma or sarcoma‐like elements. They contain spindle, giant cells or a mixture of these cell types. Although rare they represent the most common spindle cell malignancies of the airways. They are most frequently seen in middle aged to elderly men with a history of heavy smoking. They can be centrally or peripherally located. Although frequently surgically respectable overall 5‐year survival is about 20% (Nappi et al. 1994). Pleomorphic carcinomas are tumours which contain spindle and/or giant cells with or without a component of squamous cell carcinoma, adenocarcinoma or large cell carcinoma. Immunohistochemical markers for keratin or EMA are frequently positive but not always so. Spindle cell carcinomas consist solely of spindle cells and usually show immunopositivity for epithelial markers. If a tumour shows heterologous elements such as malignant cartilage, bone or skeletal muscle it is designated as a carcinosarcoma. Pulmonary blastoma is a biphasic malignant neoplasm, that despite its name, occurs overwhelmingly in adults. The epithelial component resembles primitive fetal pulmonary glandular structures and the malignant stromal component consists of blunt fusiform cells. Mortality is of the order of 30 to 70% with death usually related to distant metastases.

Epithelioid haemangioendothelioma is a low grade angiosarcoma which may occur in lung, pleura, liver, soft tissue and bone. It is composed of short cords and nests of epithelioid endothelial cells, often with intacytoplasmic vacuoles, embedded in a hypocellular, myxoid, hyaline matrix. Immunostains for CD31, CD34 and factor 8 are helpful in confirming the diagnosis. In the lung it usually presents as multiple nodules typically in females (80%) often less than 40 years of age. It is often asymptomatic when first discovered and it is associated with a protracted clinical course (Kitaichi et al 1998). However, death from respiratory failure usually occurs several years after diagnosis. When it involves the pleura it can be diffuse and can mimic malignant mesothelioma both clinically, histopathologically and prognostically (Lin et al. 1996; Galateau‐Salle F 2006).

Solitary fibrous tumour These are soft tissue tumours, which can be benign or malignant, with a propensity to occur in the pleura and less frequently in the lung. They are spindle celled tumours with a variety of patterns : ‘‘patternless’’, haemangiopericytoma‐like, diffuse sclerosing and myxoid. Immunostains are negative for cytokeratin and usually positive for CD34, bcl2 and CD99. The less common malignant forms usually show a high mitotic rate (>4 mitoses per 10 hpf), abnormal mitotic figures, cellular pleomorphism and high cellularity, size greater than 10 cm, and areas of necrosis (England et al. 1989; Galateau‐Salle 2006).

Well differentiated papillary mesothelioma This tumour should be carefully separated from diffuse malignant mesothelioma because it shows a much better prognosis, there is not a close association with asbestos exposure, and there are different therapeutic implications. It is a rare tumour, more frequently occurring in the peritoneum of young women, than in the pleura (Daya & McCaughey 1990; Galateau‐Salle et al. 2004). Grossly it consists of small nodules usually less than a centimetre, in contrast to the diffuse thickening seen with diffuse malignant mesothelioma. It is characterised by stout papillary structures with myxoid cores lined by bland, cuboidal mesothelial cells without mitoses. There is little or no invasion. The tumour usually follows a benign or indolent course but occasionally progresses.

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