Periostin: a new player in cardiac myxomas

Cardiac myxoma is the most common benign cardiac tumor generally localized in the left atrium. The majority of cardiac myxomas occurs sporadically while a relatively small proportion of cases develops as a part of Carney complex syndrome. Histogenesis of cardiac myxomasis still not fully characterized, however recent data suggest an origin from subendocardium precursors which can differentiate in both endocardial and myocardial lines. Myxoma cells are organized in rings, cords and nests showing variable immunopositivity for both vascular markers CD31 and CD34, as well as for Calretinin, which has been proved to be quite useful in discriminating cardiac myxoma from mural thrombi and papillary fibroelastomas. The extracellular matrix is organized in an Alcian blue positive myxoidstroma, partially resistent to predigestion with hyaluronidase, composed of variable amounts of proteoglycans, elastin and collagen. Interestingly, vascular channels seem to develop often from myxomatous structures. We previously reported that the expression of some extracellular matrix proteins (Tenascin c) and hyaluronic acid receptor (CD44) on cell surface is involved in angiogenesis occurring during neoplastic transformation1. In addition, we confirmed the role of mast cell-derived tryptase (detected in almost cases in left atrium) in angiogenesis and in myxoma mesenchymal cells proliferation also forming pseudovascular structures2. Recent evidences suggest a key role of Periostin, a matricellular protein, in the development of endocardial cushions and atrioventricular junction as well as in cardiac remodeling of post-infarction heart. According to recent literature, Periostin action could cooperate with Tenascin-c3. In this study, a series of 13 sporadic cases of cardiac myxoma were examined by immunohistochemical analysis for the presence of Tenascin-c and Periostin. It appears that Tenascin-C and Periostin expression levels are interrelated, suggesting a synergic role in development of cardiac myxomas. Immunohistochemical staining was also performed for the myocardiocyte marker CD117. In all cases analyzed, cells were negative for CD117, confirming the absence of myofibroblastic origin. In conclusion, the detection of Periostin overespression in cardiac myxoma, combined with the absence of CD117-positive cells strongly corroborate the idea that cardiac myxoma cells originate from precursors of cushion endocardium.