Malignant melanoma is a highly aggressive neoplasm with widespread potential for metastasis, variable clinical presentations, and unpredictable behavior. It arises from neoplastic changes in melanocytes located in the skin, mucous membranes, gastrointestinal tract, eyes, or meninges.[4] CMMM typically presents as a multifocal pericardial or myocardial mass, rarely involving endocardial cavities. When it does involve the endocardium, it is often found as a multifocal mass with dynamic changes in signs and symptoms.[1,3] Clinical presentations vary from asymptomatic cases to highly unstable patients, depending on the tumor’s size and location. Such tumors are typically fast-growing with a high potential for deep cardiac invasion. Tumor-induced obstruction of cardiac flow may result in syncope, cardiac arrest, arrhythmias, or embolic events.[5] Thus, CMMM should be considered a potentially dangerous but treatable condition.

Historically, CMMM was an incidental autopsy finding in 47%-64% of patients with melanoma postmortem.[1,2] In most cases, CMMM was clinically silent with unclear medical significance, and its clinical importance may be underestimated.

CMMM can theoretically arise from any primary melanoma site or from endocardial or myocardial tissue. Histological confirmation is essential but challenging in living patients. Percutaneous heart biopsies are difficult, so CMMM is easier and safer to confirm through surgical excision during open heart surgery. Histological proof of atypical melanocytes and dense intracytoplasmic melanin pigment is critical to confirm the diagnosis.[1,6,7]

Today, thanks to advances in echocardiography, CMMM is relatively easy to detect. It is often misdiagnosed as valve vegetation or another type of mass due to similar echocardiographic appearances. TEE is considered the optimal imaging technique for CMMM, while cardiac catheterization, CT, or MRI may be used to assess associated cardiac malformations and tumor involvement. A PET scan is mandatory to locate the primary melanoma.[1,3]

There is no standardized treatment for CMMM. Urgent surgical excision should be performed as early as possible, particularly in symptomatic cases. In our case, we approached the tumor via the right atrium, which allowed for a clear, sharp excision while preserving the tricuspid valve and right atrium. A thrombus on the tumor surface is an important finding, supporting the theory that recurrent embolization could result from CMMM embolization and secondary endothelial damage with thrombosis.

CMMM carries a poor prognosis due to extensive intracardiac infiltration and/or non-cardiac metastasis.[2] Standard chemotherapy has yielded 5-year survival rates of 5%-10%, but outcomes have improved since the introduction of immunotherapies in 2011.[2,4,5]

A potential limitation of this case presentation could be the lack of long-term follow-up data. Although the patient was reported to be symptom-free and well 6 months after surgery, malignant melanoma is known for its high recurrence rate, even decades after initial diagnosis. Without extended follow-up over several years, it is difficult to assess the long-term outcomes of the patient, including the possibility of recurrence, metastasis, or late complications from both the melanoma and the surgical intervention.

Additionally, another limitation could be the absence of detailed information on the patient’s post-surgical treatment plan, including specific immunotherapies or chemotherapies used, and their efficacy over time. This would provide valuable insight into how current therapies influence survival rates and recurrence in patients with CMMM.