Cardiac myxoma, light micrograph. Cardiac myxoma is the most common primary tumour of the heart (50% of all cases). It is benign (non-cancerous) with no known potential for malignant transformation. The most common location is the left atrium. Sporadic cardiac myxomas (90-95% cases) are usually single and occur more commonly in middle-aged women (avg. age 50 years). Familial tumours (5-10% cases) occur in younger patients, may be multicentric (30% of cases), and are slightly more common in males. They are seen in the setting of an autosomal dominant multisystem syndrome called Carney complex. The tumour cells are round, polygonal or elongated and closely associated with vascular spaces around which they for one or more concentric layers. The background stroma is myxoid and contains scattered chronic inflammatory cells.