Primary cardiac neoplasms: do effective treatments exist
Noel, Vanesa Barbara
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Primary cardiac neoplasms (PCNs) represent the rarest form of neoplastic growths worldwide with an incidence ranging from 0.001 - 0.3% in autopsy series (Yu et al., 2014) ("Primary Cardiac Neoplasms," 2014). The rarity of these tumors has contributed to the challenges associated with their diagnosis and treatment ("Primary Cardiac Neoplasms," 2014). Primary heart tumors are generally classified as benign or malignant based on whether or not the tumors cells invade their surrounding tissue. Primary benign heart tumors can be further sub-classified as non-complicated or complicated. Non-complicated tumors are those that are stable, occur alone, and do not invade the cardiac conduction system. Conversely, complicated primary benign cardiac neoplasms are those that tend to break off into systemic circulation increasing the risk for embolization, have multicentered origins within the heart and/ or invade the cardiac conduction system which may lead to heart block and sudden death ("Cardiac Tumors: Merck Manual Professional," n.d.). These distinctions have been shown to significantly impact the efficacy of treatment. Primary tumors in general tend to involve either the myocardium, i.e. the heart muscle itself, or the endocardium; i.e. the membrane that lines the heart cavities. In either case, the tumors most often appear in the left atrium (Roberts, 2001). Among primary cardiac neoplasms, myxomas (a type of non-cancerous heart tumor) are the most common accounting for approximately 40-50% of these growths ("Primary Cardiac Neoplasms," 2014). Clinicians tend to rely heavily on imaging procedures for the diagnosis of primary heart tumors because there are no characteristic clinical signs exclusive to primary cardiac neoplasms (Bartoloni & Pucci, 2013). Further, these growths have a tendency to mimic the symptomology of other better known conditions such as heart failure, stroke, and coronary artery disease ("Cardiac Tumors: Merck Manual Professional," n.d.). The mean age of diagnosis for these tumors is approximately 50 years of age but many PCNs have been identified in children (Bartoloni & Pucci, 2013; "Primary Cardiac Neoplasms," 2014). Further, sources disagree on the relative incidence of these neoplasms among men and women. Some report a higher prevalence in women while others hold that the frequencies are equal for both sexes and across all races (Bartoloni & Pucci, 2013; "Primary Cardiac Neoplasms," 2014). The standard of care for the treatment of primary cardiac neoplasms are; as with other neoplastic conditions; radiation therapy, chemotherapy, surgical resection, and; in some instances; cardiac transplantation. However, due to the differences in tumor histology, i.e. the structure and molecular characteristics of tumor cells, many of the current treatment options available to and considered curative in patients with non-complicated benign PCNs do not confer the same survival benefits in patients with complicated benign PCNs nor in patients with malignant PCNs. With treatment, the prognosis associated with primary cardiac neoplasms is heavily dependent upon the type of tumor. Primary benign non-complicated neoplasms tend to have very positive prognoses. Even with incomplete resection, reports have shown no evidence of recurrence in patients with this tumor type (Jr et al., 1987). On the other hand, primary malignant neoplasms of the heart are associated with the poorest prognoses. The longest reported median survival time is only 16.5 - 17 months after diagnosis and surgical excision of the primary tumor (Chahinian, Gutstein, & Fuster, 2000; Ostrowski, Marcinkiewicz, Kooemider, & Jaszewski, 2014; Simpson et al., 2008). In this thesis we examine the reported outcomes of the above four forms of treatment that are regarded as the standard of care for primary cardiac neoplasms. We do this by reviewing the currently available literature characterizing the results of these respective courses of therapy. We then evaluate the efficacy of these treatments relative the definition of effective treatments developed herein. Finally, based on the evidence, we conclude that effective treatments do exist for approximately 38% of people with PCNs. This minority represents the people with primary benign non-complicated cardiac neoplasms. We also regrettably conclude that for the other 62% (37% with benign complicated cardiac neoplasms and 25% with malignant cardiac neoplasms) of people with primary cardiac tumors effective treatments do not exist. For this reason, we propose the further investigation of two promising therapies. These are cardiac autotransplantation and targeted gene therapy. We believe that elucidating the possible advantages of these therapies in the heart will lead to treatments that can be deemed effective in treating complicated primary benign cardiac neoplasms as well as primary malignant cardiac neoplasms.
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