CLEAR-CELL CARCINOMA OF THE LUNG - USE OF IMMUNOHISTOCHEMISTRY TO DETERMINE PRIMARY VS METASTATIC ORIGIN

Focal clear cell change is quite common in pulmonary squamous and aden ocarcinomas. On the other hand, pure clear cell carcinoma of the lung is very rare. The World Health Organization classification defines cle ar cell carcinoma of the lung as a variant of large cell carcinoma con taining more than 50% of cells with clear, foamy cytoplasm without squ amous or glandular differentiation. It is critical to distinguish a pr imary clear cell carcinoma of the lung from a metastatic carcinoma, es pecially renal cell carcinoma. We present a 48 year old female and a 6 0 year old male with primary clear cell carcinoma of the lung. The fem ale patient died of respiratory failure, with suspicion of metastatic disease 12 mo after surgery. The male patient underwent a lobectomy an d remained free of disease for 5 yr, after which he was lost to follow -up. Histologically, more than 90% of both neoplasms were composed of optically clear cells reminiscent of renal clear cell carcinoma. There was no squamous or glandular differentiation. Differential cytokerati n immunohistochemistry could not unequivocally distinguish these neopl asms from clear cell carcinomas of other origin. Nevertheless, the ove rall immunohistochemical profile was helpful in suggesting the primary nature of these neoplasms.