Airspace invasion in
lung cancer has been known over the last 30 years, but it was only recently that WHO 2015 formally recognized it as a mechanism of invasion with the terminology of
tumor spread through air spaces (
STAS). Multiple studies have shown the association of
STAS with lower survival and suggest that
STAS is an independent prognostic factor across
lung adenocarcinoma of all stages and in other histologic subtypes of
lung cancer as well. Consequently,
STAS is designated as an exclusion criterion of
adenocarcinoma in situ and minimally invasive
adenocarcinoma; thus, the presence of
STAS impacts the diagnosis and staging of
lung adenocarcinoma. Further, wedge resection and
segmentectomy have been increasingly applied for small node negative
tumors and the presence of
STAS in those specimens may indicate the requirement of completion lobectomy. Given these significant clinical implications, we, pathologists, need to recognize and appropriately report
STAS (possibly including at the time of intraoperative consultation). However, emerging data suggests that more work should be done to improve consensus and identification of
STAS, including at frozen section. In this review, the evolution of our understanding of airspace invasion over the past decade, the clinical significance of
STAS, and controversies and practical issues associated with the diagnosis of
STAS are discussed.