Spindle cell subtype of pulmonary clear cell tumor with prominent calcification and malignant potential.

Perivascular epithelioid cell tumor of the lung, also known as clear cell "sugar" tumor, is a rare benign tumor arising from perivascular epithelioid cells. Herein, we present a case of spindle cell subtype of pulmonary perivascular epithelioid cell tumor with prominent calcification and malignant potential in a 49-year-old woman. Histologically, the striking feature of this lesion was attributed to the presence of spindle cells arranged in a diffuse pattern, which is a pitfall for diagnosis. However, some of the lesion contained polygonal tumor cells with clear abundant cytoplasm surrounded by thin-walled vascular spaces. The size of the tumor and its Ki-67 index suggested malignant potential, and calcification was another rare characteristic. Immunostaining indicated that the tumor cells were positive not only for HMB-45 and Melan A, but also for CD34 and CD1a. This tumor should be distinguished from tumors with rich spindle cells such as sarcoma, clear cell carcinoma, or metastatic tumors. The patient in this case was alive with no tumor recurrence or metastasis six months after lobectomy.