Uncommon of the Uncommon: Malignant Perivascular Epithelioid Cell Tumor of the Lung
A 63-year-old male nonsmoker with chest radiograph's abnormality was referred to our hospital. He was asymptomatic and denied any weight loss, cough, wheezing or hemoptysis. Physical examination and laboratory results were unremarkable.\nThe chest radiograph showed a large mass in the left lower lung zone, abutting the mediastinal structures (). On computed tomography, a 9 × 12-cm-sized, well-circumscribed, and solid mass was located in the posteromedial aspect of the left lower lobe with wide pleural attachment. There was no displacement of bronchovascular bundles in adjacent lung parenchyma and bone remodeling. Close observation disclosed air-bronchograms in the peripheral portion of the tumor. For these reasons, this tumor seemed to be originated from the lung parenchyma rather than the posterior mediastinum or pleura. The mass contained curvilinear calcifications and showed heterogeneous enhancement (solid portion showed strong contrast enhancement; 37 HU on pre-contrast image and 115 HU on post-contrast image) with contrast-medium injection. On the lung window image, several discrete subcentimeter nodules were also noted in both lungs, raising the possibility of lung-to-lung metastases. There was no significant mediastinal or hilar lymph node enlargement. Our final radiological differential diagnosis included lung cancer or malignant sarcoma of the lung. 18F-FDG PET CT depicted a hypermetabolic mass with SUVmax of 4.4 in the left lower lobe and several small nodules with faint uptake.\nThe patient underwent left lower lobectomy. Video-Assisted Thoracoscopic Surgery resection was planned initially but was converted to an open thoracotomy due to severe adhesion and large mass size. On the surgical field, the tumor appeared to be a lung parenchymal lesion, probably originating from the lung parenchyma near to the left lower lobar bronchus. On gross pathologic examination, the tumor appeared as a yellow-tan, well-demarcated mass with internal hemorrhage. The left lower lobar bronchus and the visceral pleura were involved with the tumor.\nMicroscopic examination showed sheets of round to polygonal cells with little clustering. The tumor cells had abundant clear to eosinophilic cytoplasm with oval nuclei (). Histopathologic differentiation included clear cell pulmonary carcinoma, metastasis from renal cell carcinoma, malignant form of paraganglioma, and PEC tumor. The tumor cells were immunoreactive for SMA, S-100 and CD56, but were nonreactive for cytokeratin AE1/AE3, HMB45, CD10, CD34, chromogranin and synaptophysin. According to these results, other histopathologic differential diagnoses other than the PEC tumor were excluded. Thus, the histopathologic diagnosis was reported as the clear cell (sugar) tumor of the lung (i.e., PEC tumor), low grade malignancy. The Ki-67 score was 10% and there was no vascular, lymphatic or perineural invasion. Tumor resection margin was negative for malignancy. At ultrastructural analysis using electron microscopy (not shown), PECs contained microfibrillar bundles with electron-dense condensation.\nA follow up CT obtained 4 months after the operation revealed enlarged metastatic nodules in both lungs. Compared with the pre-operation CT, the lesion in RLL increased in diameter from 3.8 mm to 7.3 mm within 6 months and then to 9.4 mm within another 6 months. Multifocal wedge resection for the several nodules was performed after 1 year from the initial operation and led to the diagnosis of metastatic lesions from the PEC tumor. However, there are still remaining metastatic lesions, gradually enlarging in size on a serial follow up CT.