Cardiac tumor comprising two components including typical myxoma and atypical hypercellularity suggesting a malignant change.

BACKGROUND: Cardiac myxoma is a benign neoplasm and is not considered to carry a risk of malignant transformation. We describe a case of a cardiac tumor comprising typical myxoma and atypical cellular parts.

METHODS AND RESULTS: A 72-year-old woman was found to have a tumor in the left atrial chamber after undergoing echocardiographic investigation and so she underwent tumor excision surgery. The excised tumor was composed of two components with different features with a smooth transition from one type to the other. The apex of the tumor showed a gelatinous and villous appearance on gross examination, and histological examination revealed that the tumor cells had small oval nuclei and eosinophilic cytoplasm and were arranged in cords and vasoformative structures in the myxoid matrix. The base of the tumor appeared as a solid mass on gross examination with hypercellular proliferation of spindle-shaped tumor cells and intersecting fascicles observed histologically. Nuclear mitosis was seen in more than 10/10 high-power fields, coagulation necrosis was prominent, and invasion of the atrial wall was seen. On immunohistochemistry, the tumor cells were found to be positive for alpha-smooth muscle actin, calretinin, and CD34, and this immunoreactivity was decreased at the tip. Ki-67 labeling index was increased at the apex.

CONCLUSIONS: We diagnosed this tumor as cardiac myxoma with an atypical hypercellular component suggesting a malignant change. It is important to recognize that a cardiac myxoma could be accompanied by atypical change.