RHABDOMYOSARCOMA OF PULMONARY ARTERY TRUNK.
Primary sarcomas of the pulmonary artery are uncommon. Approximately, 150 cases have been reported in world literature. The majority of these sarcomas grow along the intimal surface of the vessel in a sheet-like manner (intimal sarcoma) and are believed to originate from pluripotential mesenchymal cells of the intima. Less commonly, pulmonary artery sarcomas arise from the muscular wall or adventitia of the vessel. These mural sarcomas are better differentiated and may be difficult to differentiate from primary sarcomas of the lung.
Sarcomas of the pulmonary artery show a slight female predominance (1.3:1) with a mean age at presentation (48 years) younger than the mean age of patients with aortic sarcomas (62 years) and caval sarcomas (54 years). The clinical presentation is usually that of embolic lung disease. Most common symptom is dyspnea, followed by chest pain, cough, hemoptysis and constitutional symptoms. Patients are often given anticoagulants before a tissue diagnosis is rendered.
Chest X-ray may be normal or may show a hilar mass, prominent pulmonary artery shadow, hilar infiltrates, decreased pulmonary vascular markings or metastatic pulmonary nodules. Gadolinium-enhanced magnetic resonance imaging shows a heterogenous enhancing filling defect of pulmonary artery and is helpful in differentiating vascular neoplasm from organizing thromboemboli. Angiography demonstrates the extent of the lesion within the pulmonary vasculature. In one recent study, the combination of MRI, angiography, computed tomography and pulmonary scintigraphy was accurate in preoperative diagnosis of intraluminal neoplasm in 7 of 8 patients. Prior to the use of these powerful techniques, a diagnosis of pulmonary artery sarcoma was made at post mortem examination.
Grossly, the sarcoma resembles a mucoid clot filling the affected vessel. Bony or gritty areas correspond to areas of osteosarcoma which is frequently present. Sites of attachment are multiple and difficult to define. The main pulmonary trunk is involved in 80% of the cases, left main pulmonary artery in 58% and right pulmonary artery 57%. The tumor often extends distally along the lumen of pulmonary arterial branches and may infiltrate into lung parenchyma or may extend proximally to involve the right ventricle.
Intimal sarcomas of the pulmonary artery are typically spindle cell proliferations in a myxoid background. Approximately, 50% are fibroblastic or myofibroblastic sarcomas that are not further classified and 20% are leiomyosarcomas. The remaining 30% have been classified as chondrosarcomas or osteosarcomas (7%), rhabdomyosarcoma (6%), malignant mesenchymoma (6%), angiosarcoma (7%), malignant fibrous histiocytoma (3%) and liposarcoma (1%).
Immunohistochemistry shows strong expression of vimentin with variable expression of smooth muscle actin, desmin, muscle specific actin and myosin. Weak focal expression of epithelial markers has been described. Immunoreactivity for neural markers has not been reported thus far. Although these findings are non-specific, they are compatible with myofibroblastic origin of the majority of these neoplasms. Ultrastructurally, there may be microfilaments with dense bodies within tumor cells and discontinuous basal lamina; these features are also compatible with a myofibroblastic derivation. Since there are no unequivocal histopathologic or immunohistochemical markers of intimal sarcoma, classifying the pulmonary artery as the site of primary tumor has to be confirmed through comprehensive clinical staging.
Bode-Lesniewska et al. have described a weak focal immunoreactivity with c-kit, p53 and mdm-2 protein. There is growing evidence that c-kit protein, previously considered highly sensitive for gastrointestinal stromal tumors, is expressed in other mesenchymal neoplasms including some vascular tumors (angiosarcomas and some cases of Kaposi's sarcoma). With the availabilty of substances modifying the c-kit pathway, additional studies need to be performed to determine the true expression of c-kit protein in pulmonary artery sarcomas.
Little is known about molecular changes in pulmonary artery sarcomas. In their case series, Bode-Lesniewski et al. found gains and amplifications of 12q13-14 region with over-expression of mdm2 proto-oncogene as the most frequent genetic alterations. Other changes include deletions of chromosome 13 (suggestive of loss of Rb gene) and gains and amplifications of 17p and 17q.
Sarcomas of pulmonary artery are less likely to metastasize than their counterparts in aorta. However, metastases to the lung, kidney, brain, lymph nodes, adrenal glands and skin have been reported. Mean survival from initial presentation is 18 months. Patients in whom curative resection is attempted have a longer disease free course than those without surgery. The role of chemotherapy and radiation therapy in management of patients with pulmonary artery sarcomas remains unclear.
Contributed by Hina Sheikh, MD, Remigio Gregorio, MD and Samuel Yousem, MD