Pleomorphic carcinoma of the lung expressing podoplanin and calretinin.

Pleomorphic carcinoma (PC) of the lung is classified as a subtype of sarcomatoid carcinoma of the lung, and peripheral PC is sometimes difficult to differentiate from the sarcomatoid component of mesothelioma. An 80-year-old man was referred to National Cancer Center Hospital East because a chest X-ray showed an abnormal shadow. CT scans of the chest indicated two solid masses located in the right lower lobe, and CT-guided needle biopsy yielded spindle-shaped tumor cells that were immunoreactive for both podoplanin and calretinin. Mesothelioma could not be ruled out, and the tumors were surgically resected to facilitate definitive pathological diagnosis. Both tumors were composed of undifferentiated carcinoma, bronchioloalveolar carcinoma and spindle cell carcinoma, and spindle cell component was immunoreactive for podoplanin and calretinin. Ten other tumors diagnosed as peripheral PC were also tested for podoplanin and calretinin expression. The sarcomatoid component in four of the 11 cases (36%) was immunoreactive with podoplanin, and it was calretinin positive in nine of the 11 cases (82%). When making the differential diagnosis between PC and the sarcomatoid component of mesothelioma, care is required in diagnosing biopsy specimens of peripheral lung spindle-cell tumors that are positive for both podoplanin and calretinin.