Table 1. Studies applied divergent definitions of STAS and/or related morphological features.

Study	Entity	Number of cases	Stage	Definition of STAS or related features
Onozato et al. 2013 (7)	ADC	261	I–II	Isolated, large collection of tumor cells present within alveolar spaces that lacked well-demarcated micropapillary configuration. The islands were located at the periphery of the tumor and were separated by at least a few alveoli
Kadota et al. 2015 (1)	ADC	411	I	Micropapillary clusters, solid nests, or single cells spreading within air spaces beyond the edge of the main tumor
Warth et al. 2015 (2)	ADC	569	I–IV	Detachment of small cell nests (at least 5 tumor cells) <3 alveoli away from the main tumor mass (limited STAS) and tumor cell nests >3 alveoli away from the main tumor mass (extensive STAS)
Morimoto et al., 2016 (10)	ADC	67	I–III	A group of more than 3 small clusters containing <20 nonintegrated micropapillary tumor cells that were spreading within air spaces, >3 mm apart from the main tumor
Shiono and Yanagawa, 2016 (11)	ADC	318	I	Tumor cell clusters lying freely within the alveolar space at a distance of at least 0.5 mm from the main tumor
Lu et al., 2017 (12)	SCC	445	I–III	Tumor cell nests identified beyond the edge of the main tumor even if present only in the first alveolar layer from the tumor edge
Uruga et al., 2017 (13)	ADC	208	I	Micropapillary clusters, solid nests, or single cells spreading within air spaces beyond the edge of the main tumor. Cases were further classified as no STAS, low STAS (1–4 clusters of micropapillary or solid nest-predominant STAS), or high STAS (≥5 clusters of STAS)
Dai et al., 2017 (14)	ADC	554	I	Tumor cells observed within air spaces in the surrounding lung parenchyma beyond the edge of the main tumor. It was classified into three morphologic subtypes: (I) single cells, (II) micropapillary clusters, and (III) solid nests

STAS, spread through air spaces; ADC, adenocarcinomas; SCC, squamous cell carcinomas.