Two Cases of Resected Bronchiolar Adenoma/Ciliated Muconodular Papillary Tumor Requiring Differentiation from Peripheral Lung Cancer.

introductionBronchiolar adenoma/ciliated muconodular papillary tumors (BA/CMPTs) are rare benign tumors. Because their radiological appearance often resembles that of small peripheral lung cancers, preoperative differentiation remains challenging. Furthermore, BA/CMPTs may be misdiagnosed as adenocarcinomas during intraoperative frozen-section consultations. Here, we report two cases of resected BA/CMPTs with distinct radiological morphologies and discuss their clinicopathological characteristics compared with those of previously reported cases. CASE PRESENTATION: The first case involved a 69-year-old man who presented with an 8-mm solid nodule in the right lower lobe. Primary lung cancer (cT1aN0M0, cStage IA1) was suspected, and video-assisted thoracoscopic wedge resection of the right lower lobe was performed for diagnostic and therapeutic purposes. Intraoperative frozen section evaluation suggested adenocarcinoma; however, no additional resection was performed in accordance with a planned limited approach considering the comorbidities, including chronic kidney disease. Permanent sections revealed a bland bilayered epithelial proliferation with focal ciliated epithelium. Immunohistochemical analysis revealed a continuous basal cell layer positive for CK5/6 and p40, leading to the final diagnosis of BA/CMPT. The second case involved a 77-year-old man who presented with a 9-mm pure ground-glass nodule (GGN) in the right lower lobe. Early lung adenocarcinoma (cTisN0M0, cStage 0) was suspected. Following preoperative CT-guided marking, video-assisted thoracoscopic wedge resection was performed. Permanent sections showed no significant cytological atypia, focal ciliated epithelium, or a continuous basal cell layer highlighted by CK5/6 and p40, confirming BA/CMPT. After complete resection, both patients were followed up without adjuvant therapy.

conclusionsBA/CMPTs can present with diverse radiological appearances, ranging from small solid nodules to pure GGNs, and typically show slow interval growth, making their differentiation from small peripheral lung adenocarcinoma challenging. Moreover, the evaluation of cilia and the basal cell layer is often limited in frozen sections, which may lead to misdiagnosis as adenocarcinoma. Therefore, awareness and shared recognition of this entity is essential to avoid overtreatment such as lobectomy and systematic lymph node dissection. Further accumulation of cases is warranted to refine the diagnostic criteria and optimize the management strategies for BA/CMPTs.