Background: Myofibroblastic tumor is a relatively new nosologic entity sharing similar features with a smooth muscle tumor. The low-grade myofibroblastic sarcoma (LGMS) is an intermediate- or low-grade malignant myofibroblastic neoplasm.
Case: The patient was a 63-year-old Asian male whose cardiac imaging revealed a right atrial mass suggestive of myxoma measuring 8.70 cm in widest diameter and with a chest CT-scan that showed bilateral pulmonary masses. The atrial mass was excised and a subsequent fine needle aspiration of the right pulmonary mass was performed. Within two months of presentation, patient's disease progressed and eventually died.
Results: Microsections of the atrial mass revealed a tumor composed of fascicles and sheets of spindle cells in a variable fibromyxoid matrix with mitoses of 1-5/10 HPF and necroses. The abundance of myxoid stroma simulated features of myxoma. Immunohistochemistry showed focal reactivity to smooth muscle actin (SMA) and desmin, and non-reactivity to h-caldesmon. Proliferation studies using Ki-67 and p53 were 40% and 10% respectively. The histologic findings of the atrial mass were compatible with a low-grade myofibroblastic sarcoma. The CT-scan guided fine needle aspiration of the pulmonary mass showed similar spindle cells in myxoid matrix. Immunohistochemistry showed non-reactivity to thyroid transcription factor-1 (TTF-1), pancytokeratin, and synaptophysin, and with a proliferation index of 20-25% using Ki-67. The aspirate findings were consistent with a tumor metastatic from the cardiac tumor.
Conclusion: The application of the panel of immunohistochemical stains can aid in the diagnosis of a myofibrolastic sarcoma in particular h-caldesmon, which when negative, rules-out smooth muscle tumors. The proliferation index is a vital clue in the disease course even if the histology appears low grade.