Clear-cell proliferation of the lung with lymphangioleiomyomatosis-like change

Aims : To describe two cases of a peculiar pulmonary lesion, which expand both the morphological and the immunophenotypic spectrum of perivascular epithelioid cell (PEC)‐related disorders. Methods and results : One man and one female, with and without the tuberous sclerosis complex (TSC), respectively, showed pulmonary cysts and small nodules on computed tomography scan. In the former, lymphangioleiomyomatosis (LAM) was suspected. In both cases, an open lung biopsy was performed, whose cut surface displayed numerous cysts lined by thin/thick septa. Microscopically, the septa were associated with micronodular or interstitial proliferation of medium/large‐sized elements with abundant clear (periodic acid–Schiff‐positive/diastase‐sensitive) cytoplasm and distinct cell borders, embedded in fibrous tissue. The elements were CD34+, vimentin‐positive and, to a lesser extent, HMB‐45+ and MART‐1+. The stains for specific muscle actin, desmin, S100 protein, CD31, FVIIIRAg, cytokeratins, CD45, CD68, oestrogen and progesterone receptors were all negative. Ki67 labelling was