Objective To analyze the clinicopathological features, diagnosis and differential diagnosis of bronchiolar adenoma (BA) with primary lung cancer.

Methods Data of 17 BA patients complicated with primary lung cancer in Dalian University Affiliated Xinhua Hospital from January 2020 to December 2022 were collected, and the clinical data, histopathological features and immunohistochemical features were summarized.

Results 17 patients included 7 males and 10 females, with 49-82 years old. There were 2 squamous cell carcinoma and 15 adenocarcinoma. BA was mostly nodular, without capsule. It had a clear boundary with the surrounding lung tissue, with a major diameter of 0.3-1.5 cm. The section of BA was gray-white, gray-red, gray-brown, with medium-soft texture, and a few had obvious mucus. Microscopically, it was composed of luminal cell layer and basal cell layer, and luminal cells contain mucus cells, ciliated cells, cubic cells and columnar cells. According to the composition of luminal cells, BAs were divided into proximal type and distal type. There were 5 proximal type and 12 distal type, including 1 case of atypical distal BA. Immunohistochemistry results showed that in typical BAs, CK5/6, p63 and p40 were positive in basal cells, thyroid transcription factor-1 was positive in luminal cells and basal cells, and the proliferation index of Ki-67 was 1%.

Conclusions BA is a benign tumor, and is a bilayer structure mainly composed of luminal cells and basal cells. However, when the absence or discontinuity of basal cells, BA is easily misdiagnosed as malignancy, which should be highly vigilant.