Pulmonary pleomorphic carcinoma arising in mixed squamous and glandular papilloma: A case report.

Solitary pulmonary papillomas (SPPs) are rare lung neoplasms. Histologically, SPP is classified into three subtypes, and mixed squamous and glandular papilloma (MP) is the rarest subtype. Although SPPs are considered benign tumors, there have been several reports on the synchronous malignant transformation in SPPs. An 82-year-old asymptomatic man was referred to our hospital for further examination of a 2.2 cm-sized left lung tumor. Pathology of bronchoscopic specimens showed the possibility of pulmonary papilloma but did not reveal any malignancy. The patient complained of bloody sputum during the eighth month after the initial visit. The size of the lesion had increased to 4.3 cm. These data suggested the existence of malignancy, and the patient underwent an operation. Histologically, the tumor was composed of fibrovascular cores and papillomatous fronds lined by pseudostratified columnar cells and mucin-filled goblet cells. Keratinizing squamous epithelium was also observed. Overall, the diagnosis of MP was obtained by fundamental histology. In addition, a solid part beneath mild atypical squamous epithelia, which was composed of malignant-appearing squamous cells and spindle-shaped atypical cells, was observed. The spindle portion was positive for cytokeratin AE1/AE3 and vimentin, and focally positive for alpha-smooth muscle actin (αSMA). The final diagnosis was pulmonary pleomorphic carcinoma (PPC) arising in the MP. Only two cases have been reported for atypical spindle tumor cells that are found in MP or bronchiolar adenoma/ciliated muconodular papillary tumor (BA/CMPT), which has histologically similar features to MP. This is the second case report of PPC arising in MP.