Clinicopathological analysis of bronchiolar adenoma combined with lung adenocarcinoma: Report of eight cases and literature review

Abstract

Aims. To investigate the clinicopathological characteristics and potential diagnostic pitfalls of bronchiolar adenoma (BA) combined with lung adenocarcinoma (LUAD) in the same lesion. Methods. We analyzed eight cases of BA combined with LUAD from our hospital pathology department between July 2020 and January 2022, and summarized their clinical data, radiological features, histo-pathological characteristics and immunohistochemical phenotypes. Results. Upon macroscopic examination, the lesions were characterized by gray-white or gray-brown solid nodules with well-defined borders, measuring 0.6-1.8cm in maximum diameter. The incidence of proximal-type BA (6/8) was higher than that of distal-type BA (2/8), and they combined with different stages of LUAD, including adenocarcinoma in situ, minimally invasive adenocarcinoma, invasive adenocarcinoma, and invasive mucinous adenocarcinoma (IMA). Immunohisto-chemistry showed that cytokeratin 5/6 and P40 were positive in the continuous basal cell layer in BA, but only scattered positive basal cells were seen at the junction of BA and LUAD. TTF-1 was positive in proximal-type BA ciliated cells in five cases and in LUAD cells in seven cases, and weakly positive in some basal cells. One case of IMA and mucinous cells of BA were TTF-1 negative. There was partially positive Napsin-A expression in BA luminal cells and LUAD cells of all cases except IMA. Conclusion. There is no obvious boundary when BA and LUAD are in the same lesion. The luminal epithelial cells in the area where the two components migrate toward each other are atypical and lack a continuous underlying basal cell layer. Microscopic diagnosis should be aided by immunohistochemistry.