Clinicopathological characteristics and immunophenotype of six cases of cardiac myofibroblastic sarcoma in a single tertiary hospital, Philippine Heart Center, from 2000 to 2018

Myofibroblastic sarcoma (MS) is a rare malignant tumor of myofibroblast. Myofibroblasts were primarily described by Gabbiani et al. by means of electron microscopy. These spindle cells have features common with smooth muscle cells and fibroblast. Vasudev et al. first reported the pathologic characteristics of MS in 1978. Mentzel et al. coined the term “low-grade MS” after immunohistochemical and ultrastructural profiling in a series of cases. This study was undertaken to analyze the clinicopathologic, histopathologic, and immunohistochemical characteristics of MS cases arising in the heart. This is a descriptive study performed at the Philippine Heart Center. All twelve cases diagnosed as cardiac MS and other cardiac spindle cell tumors included in the Philippine Heart Center Pathology Cardiac Registry from 2000 to 2018 were reviewed. Six of the twelve cases were later proven or reclassified as MS. The six patients with MS were composed of three males (50%) and three females (50%) with a mean age of 57.5 and SD of 9.91. Four of the cases were from the left atrium (68%), one was from the right atrium (16%), and one was biatrial (16%). The tumor size ranged from 3.0 to 8.7 cm with a mean size of 5.57 cm and SD of 1.60. All six cases were treated surgically; four by excision (68%), one by debulking (16%), and one by both excision and debulking (16%). Histologically, the six tumors were predominantly composed of pleomorphic to monomorphic spindle cells arranged in syncytium, storiform, fascicles, and dense cellular sheets, some are intersecting at angles. The individual tumor cells are spindled with elongated nuclei with blunted ends, granular to open chromatin pattern, inconspicuous nucleoli, and scanty to moderate amount of eosinophilic to amphophilic cytoplasm. Cytoplasmic membrane are indistinct. Lymphoplasmacytic infiltrates are present with a mean of 28.67 per 10 high power fields, range of 7-91, and SD of 33.07. Mitosis are present with a mean of 12.17 per 10 high power fields, range of 3-32, and SD of 10.93. Necrosis of less than 50% is present in 4 of 6 cases (67%). Two cases (33%) showed no necrosis. Trichrome stain showed collagen deposits in five of six cases (83%). Immunohistochemically, all six cases of MS showed reactivity for vimentin and smooth muscle actin (100%). Three of six cases were reactive to calponin (50%). All six cases show non-reactivity against h-caldesmon (0%). Two of the six cases were reactive with desmin (33%). Two of the six cases were reactive with CD99 (33%). Only one of six cases were reactive to pancytokeratin (17%). No significant differences between proliferation indices using Ki-67 and p53 were observed. The application of the panel of immunohistochemical stains can aid in the diagnosis of MS in particular h-caldesmon which when negative rules-out smooth muscle tumors. MS consistently expresses vimentin and smooth muscle actin. Expression of calponin, desmin, and CD99 is variable. Prognostic value of proliferation indices using Ki-67 and p53 as a prognostic indicator is not proven.