Why primary malignancies of the heart and pericardium are so rare

Introduction: Primary Malignant Cardiac Tumours (PMCTs) of the heart and pericardium are extremely rare. The incidence rate of both malignant and benign primary tumours is 0.02%, however only one quarter of these are malignant. The reason why these specific malignancies are so uncommon is not yet well understood. This review aims to determine why the heart and pericardium are such inhospitable hosts to PMCTs. Materials and methods: Literature was systematically analysed using a three-stage methodology; scientific databases were selected; a literature search was conducted and finally a shortlist of six publications was created using a criteria based selection process. Results: The hearts of 1-day-old mice were able to regenerate after partial resection, however this capacity was lost at seven days old. The terminal differentiation of cardiomyocytes is a result of early cell cycle exit, regulated by Meis1. Myocyte-specific Meis1 deletion resulted in the extension of the postnatal regeneration period and caused reactivation of cardiomyocyte mitosis. Overexpression of Meis1 inhibited cardiac regeneration and decreased neonatal myocyte proliferation. Cardiomyocytes exiting the cell cycle after seven days have less chance of being exposed to mutations. This lack of mutation accumulation results in low rates of PMCTs. Conclusions: This study has demonstrated the association between low PMCT rates and cardiomyocyte early cell cycle exit, caused by Meis1. The extremely low number of PMCT cases is a result of the heart being unable to regenerate. However, this inability to regenerate causes high incidence rates of cardiovascular disease, due to the formation of scar tissue.