Diagnostic utility of tumor volume doubling time in ciliated muconodular papillary tumor/bronchiolar adenoma mimicking invasive mucinous adenocarcinoma: A case report.

Ciliated muconodular papillary tumor (CMPT), recently categorized under bronchiolar adenoma (BA), is a rare benign peripheral lung lesion. Due to its mucin-rich nature and radiological appearance, it frequently mimics invasive mucinous adenocarcinoma (IMA), leading to potential over-treatment. While its indolent nature is known, quantitative data regarding its growth kinetics, specifically tumor volume doubling time (VDT), are lacking. We present a case of CMPT/BA with a 3-year observation period and evaluate its diagnostic utility via VDT calculation. A 72-year-old female with a history of smoking and treated cecal adenocarcinoma presented with an enlarging 1.2 cm irregular, cavitary nodule in the right middle lobe. The lesion had been monitored for 3 years, showing a gradual growth of approximately 0.3 mm every 6 months. Suspecting primary lung cancer or metastasis, a diagnostic resection was performed. Intraoperative findings showed a glistening, mucinous lesion suggestive of IMA, prompting a right middle lobectomy. However, histopathology revealed a tri-layer epithelial composition including ciliated columnar, mucinous, and basal cells. Immunohistochemistry confirmed a continuous basal cell layer (p63/p40 positive) and thyroid transcription factor-1 positive surface epithelium, diagnostic of CMPT/BA. Retrospective 3-dimensional computed tomography volumetry determined the VDT to be 2526 days. CMPT/BA poses a significant diagnostic challenge as a radiological and intraoperative mimic of IMA. In this case, the VDT (2526 days) was markedly longer than the reported mean for IMA (approximately 440 days). Identifying such prolonged doubling times through serial imaging and volumetry can assist clinicians in suspecting benign entities like CMPT/BA, potentially facilitating appropriate treatment strategies.