Regional proliferation of HMB-45-positive clear cells of the lung with lymphangioleiomyomatosislike distribution, replacing the lobes with multiple cysts and a nodule.

The authors report a case of a localized lesion of the lung presenting as multiple cysts and as a tumor in the right upper and middle lobes, consisting of a diffuse proliferation of clear cells with intralysosomal glycogen granules and human melanin black (HMB)-45 immunoreactivity. A 33-year-old woman complained of dyspnea because of the enlargement of bullae in the right upper and middle lung fields without stigmata of tuberous sclerosis. Resection showed multiple, various-size air-filled cysts and a tumor. The cysts in the resected lungs were reminiscent of lymphangioleiomyomatosis (LAM), accompanied by the diffuse proliferation of clear cells in the interstitium. The tumor, 1.8 cm in diameter, resembled a clear cell tumor of the lung (CCTL) and showed proliferation of clear cells with sinusoidlike vascular spaces. Both forms of proliferation were continuous spatially, and both constituent cells showed diffuse HMB-45 immunoreactivity. The cells that comprised a nodule revealed ultrastructurally abundant cytoplasmic glycogen, which was in the form of free and membrane-bound glycogen granules. This case may represent a particular pulmonary lesion consisting of CCTL-LAM hybrid cells, which share the cytologic features with CCTL cells on one hand, and the proliferative pattern and potential with LAM cells on the other.