While the typical lung carcinomas are extremely common, there are a number of rare mesenchymal and miscellaneous tumors with variable presentations, prognoses and treatments. The histopathologist must be aware of these, as their rarity makes accurate diagnosis challenging. This chapter discusses these infrequent neoplasms. The etiologies of these lesions are generally unknown. Lesions are broadly grouped according to their presumed cell of origin. Some of these lesions, such as hamartoma and minute pulmonary meningothelial-like nodule, are unique to the lung, but others are included here simply owing to their presence in the lung.
Since most of these tumors have few if any clinical features suggestive of their diagnosis, it serves well to reinforce the fact that peripheral lesions are usually asymptomatic unless they are so large as to cause chest wall pain, and only detected on radiographic studies, while central tumors may cause shortness of breath, wheezing or recurrent pneumonia with eventual bronchiectasis. Slow-growing tumors may not effect such changes while rapidly growing sarcomas can present with cor pulmonale.