Clear cell carcinoma of the lung is an extremely rare type of lung can
cer with doubtful etiology. This present case showed that the tumor ce
lls contained abundant cytoplasmic glycogen with a diffusely distribut
ed pattern and intracellular glandular structure electron microscopica
lly. Immunohistochemical study revealed that the tumor cells expressed
not only epithelial marker including cytokeratin and epithelial membr
ane antigen, but also Le(y), one of stage-specific embryonic carbohydr
ate antigens. The diagnosis of pulmonary clear cell carcinoma should b
e done carefully, because benign clear cell tumor and secondary renal
cell carcinoma show similarities in a histologic appearance but not in
their management and prognosis.