Background Ciliated muconodular papillary tumor (CMPT) was initially recognized as three typical types of cells (ciliated cells, mucinous cells and basal cells) and two typical structures (papillary and tubular). It is found that the proportion of various cells is different and papillary structure is not necessary. So some scholars propose that CMPT is a proximal-type bronchiolar adenoma (BA) which expands the concept of CMPT. At the same time they propose revising the terminology. These morphological variations bring great challenges to the diagnosis.
Case presentation: Multiple small nodules in bilateral lungs were found in 79-year old female patient. A frozen examination was performed. Grossly, there were jelly-like nodules with clear boundaries, and the maximum diameter was about 4mm. Microscopically, glandular ducts, papillary and even micropapillary structures were seen. The cavities were lined by columnar cell and mucous cells. In a low-power field the conspicuous mucin pool was observed, as well as floating tumor cells in the mucin pool. So atypical adenomatous hyperplasia of the lung was reported in intraoperative rapid diagnosis, and the surgeon performed a lobectomy for the patient. In typical HE, this tumor was made up of three kinds of cells in different proportions, including ciliated columnar cells, mucous cells, and basal cells which were confirmed by CK5/6 and P63 immunohistochemistry staining. Immunohistochemical analysis reveals thyroid transcription factor1 (TTF-1) and CK7 expression by ciliated columnar epithelial cells, basal cells, and nonciliated columnar and cuboidal epithelial cells, but not mucous cells. All the cells do not express CK20. BRAF V600E protein express in the tumor. At the same time, the tumor harbores the BRAF gene mutation, while EGFR, KRAS, ALK, HER-2, RET, ROS-1, PIK3CA and NRAS mutation are negative.
Conclusion We report a classic CMPT. The tumor has BRAF mutation and BRAF protein expression. Classic lesions are easy to identify, while for morphological variant cases, the key to the diagnosis of the disease is the diversity of cell components and the presence of basal cells.