Is Spread of Tumor through Air Spaces a Concern for Interpreting Lung Nodules on CT Images?
Radiology. 2018 Dec;289(3):841-842. doi: 10.1148/radiol.2018181764. Epub 2018 Sep 4. Naidich DP1.
In this issue of Radiology, Kim et al (1) report CT features associated with tumor spread through air spaces (STAS) in patients with early stage adenocarcinoma of the lung. At the time of publication, to my knowledge, this represents the first attempt at correlating lung CT with STAS, and as such it is an important contribution to our understanding of this entity. As currently defined by the 2015 World Health Organization classification, STAS represents micropapillary clusters, solid nests, or single cells that spread within air spaces beyond the edge of the main tumor (2). Three-dimensional reconstruction has helped to show that these cells are actually connected to the main tumor (3). STAS-positive tumors have consistently been associated with high-grade tumors (especially micropapillary, cribiform, and solid adenocarcinomas), smoking, KRAS gene mutations, and higher nuclear grade. Therefore, STAS now represents a fourth category that defines tumor invasion in adenocarcinomas; in addition to histologic subtypes other than lepidic predominant lesions, this includes myofibroblastic stromal invasion, and vascular or lymphatic invasion (4). STAS has also been identified in patients with squamous cell carcinomas (5) and more recently identified in nearly all primary lung cancers. Importantly, despite variations in definition, STAS has also been consistently associated with poor prognosis, especially early recurrence after limited sublobar resections (6,7).