3D virtual histology demonstrates tumour connectivity in spread through air spaces (STAS) of non-small cell lung cancer

Introduction: As the nature of spread through air spaces (STAS) in non-small cell lung cancers (NSCLC) remains a matter of debate, this paper presented the first application of 3D X-ray virtual histology to shed light on the origin of these elements. Methods: Five adenocarcinomas and two squamous cell carcinomas were selected from a cohort of NSCLC cases to serve as representative examples of neoplasms in which the presence of STAS had already been assessed through conventional histology. Although available only for research purposes, synchrotron radiation X-ray phase-contrast micro-tomography (μCT) allows virtual sectioning of whole paraffin blocks with spatial and contrast resolution similar to that of histology, thus enabling examination of STAS patterns (e.g., single and clustered tumour cells, micropapillary, solid nests). Results: The 3D results demonstrated that free-floating STAS (i.e., micropapillary and solid patterns) were observed to be only the edges of tumour cell clusters connected to the primary tumour. In contrast, STAS located near alveolar walls or vascular structures suggested tumour cell migration along these surfaces away from the primary tumour. Conclusion: These findings indicate that most STAS types are clusters of cells connected to the main tumour mass. 3D X-ray virtual histological investigation helps to understand the morphological composition and spatial evolution of the tumour, as well as the presence of a tumour larger than that visible in the histological slide. From a radiological and surgical perspective, these findings may influence the assessment of the extent of parenchymal involvement and help guide the surgical approach.