Hematoxylin and eosin stain of transthoracic needle lung biopsy. This slide is at 40x magnification. The sections show multiple cores of lung parenchyma, some of which contain an intra-alveolar infiltrate of relatively monomorphic tumor cells with round nuclei and a moderate eosinophilic cytoplasm. The cells are set in a myxohyaline stroma. Scattered areas show intracytoplasmic lumina, and there are also intranuclear inclusions. Most of the tumor appears to be intra-alveolar and the surrounding lung parenchyma shows mildly prominent type II pneumocytes. There is no evidence of significant nuclear atypia, mitoses, or necrosis.