Spread through air spaces in lung adenocarcinoma: is radiology reliable yet?

The concept of tumor spread through air spaces (STAS) in lung adenocarcinoma was officially recognized as a pattern of invasion in 2015 World Health Organization (WHO) classification. The STAS is defined as the presence of “micropapillary clusters, solid nests, or single cells beyond the edge of the tumor into air spaces in the surrounding lung parenchyma” within the surgical specimen (Figure 1), which implies a post-surgical diagnosis (1). The pathological evidence of STAS is a negative prognostic factor, especially for early lung cancer treated by limited lung resection (e.g., segmentectomy) (2,3). Therefore, pre-surgical characterization of lung cancer features has gained much interest for the optimal surgical planning. This led to investigation of potential association of STAS with computed tomography (CT) features, as recently addressed by three research groups who aimed to radiological prediction of invasion of air by the tumor (4-6)