902 G.Y. Kim, C.O. Sung, J. Han, et al. Fig. 1. Chest computed tomography shows diffuse micronodules and ground glass opacities in both lung fields. Fig. 2. Histologic section shows numerous micronodules in the alveolar spaces (H&E, ×1). Fig. 3. Microscopically, nodules consist of short spindle cells arrang- ed in ill-defined whorls. The tumor cells have bland nuclear fea- tures and eosinophilic cytoplasm (H&E, ×200). Inset shows nucle- ar immunoreactivity for estrogen receptor (×400). (Novocastra, 1:40 dilution). The patient was well and asymp- tomatic when last seen, 8 months post thoracotomy, and the GGO was improved with repeated tamoxifen and ifosphamide therapies. DISCUSSION ESS represents approximately 15-25% of all uterine sar- comas and are separated into high and low grades, depending primarily on the mitotic index (more or less than 10 mitoses per 10 high power fields, respectively). Low grade ESS is the most common and has a favorable prognosis. Recurrence is not uncommon and tends to be limited to the pelvis. Dis- tant metastases may develop after long tumor-free intervals and the lung is the most commonly affected site. The most common growth pattern of pulmonary metastatic ESS, pre- viously described in the literatures, is well circumscribed nodules with entrapped air spaces lined by non-neoplastic respiratory epithelium (1). The unusual growth patterns are solitary nodule, satellite with infiltrative margins, lymphan- gitic pattern and bilateral spontaneous pneumothoraces asso- ciated with predominantly cystic lesions mimicking lym- phangioleiomyomatosis, which can contribute to the diag- nostic dilemma (1-5). This is especially true if clinicians and/ or pathologists are unaware of a prior diagnosis of uterine ESS. Prior misdiagnosis of a uterine tumor can also be mislead- ing, emphasizing the need to review previous surgical speci- mens, particularly gynecologic specimen in female patients with unusual mesenchymal lung neoplasms (6, 7). The micronodules of the present case did not show entrap- ped respiratory epithelium and were mainly located in the intraalveolar spaces growing out from alveolar walls suggest- ing hematogeneous spread. This pattern of metastases of uter- ine ESS is interesting and has been not reported in English literatures. We assumed that the lesions were caused by lodg- ing of microtumor emboli through the pulmonary artery. The metastatic ESS demonstrated the same range of histo- logic features seen in primary uterine ESS. The differential diagnosis includes benign metastasizing leiomyoma, sclerosing hemangioma, solitary fibrous tumor, hemangiopericytoma, and lymphangioleiomyomatosis in small biopsies. Immunohistochemical stains can be helpful in dif- ferentiation of above diseases. Immunostaining for estrogen receptor and progesterone receptor are positive in nearly all cases of uterine ESS. Immunostaining for keratin and smooth muscle markers are variable. Diffuse immunoreactivity for CD10 in uterine ESS can also be helpful in separating them from uterine smooth muscle neoplasms, which are usually negative.