Micropapillary structure of lung adenocarcinoma and spread through air space (STAS) in thick-section histology

Abstract

The patient was a 61-year-old woman, a current smoker, who presented with a solid spiculated mass in right lower lobe of the lung detected by chest computed tomography. The diagnosis of adenocarcinoma was made by aspiration cytology. Right lower lobectomy was performed, and the diagnosis of acinar predominant lung adenocarcinoma was confirmed on histology. The histology also showed isolated intra-alveolar micropapillary clusters of malignant cells around the main tumor, additionally involving lung segments beyond the main tumor. We examined 150 μm thick-sections, stained with hematoxylin and eosin, which showed these intra-alveolar cancer cell clusters in three-dimensions. This method of tissue examination confirmed that these were metastatic intra-alveolar micropapillary clusters with spread through air spaces and were not due to direct extension from the main tumor mass. In the lung, “spread through air spaces” (STAS) has been recently described as an important prognostic indicator in adenocarcinoma of the lung. In this case, tumor cells were found as micropapillary structures, cell nests, and single cells within air spaces and beyond the edge of the main tumor. Because of their association with poorer prognosis, it is important to recognize the micropapillary variant of primary lung adenocarcinoma and to identify STAS. We would recommend the use of thick-section histology in evaluation of STAS in adenocarcinoma of the lung.