Discussion:
Lung cancer is the most common malignancy worldwide, contributing to 1.8 million deaths in 2018 (2). This cancer typically metastasizes to the liver and adrenal glands via hematogenous spread (3).  Metastatic cardiac masses usually affect the pericardium due to preferential metastatic pathways involving lymphatics. Myocardial metastatic involvement from lung cancer is infrequent (4). Histopathologic differentiation of lung malignancy has a differential predilection to cardiac metastases, with lung adenocarcinoma contributing to 21% and lung SCC contributing 18.2% of total secondary cardiac tumors (1). The most common presentation of patients with cardiac metastasis depends on the type of involvement and the anatomic location. Patients can present with dyspnea, pedal edema, chest pain, palpitation due to various arrhythmias, and life-threatening presentations such as syncope, stroke, cardiac tamponade, cardiac rupture, acute myocardial infarction, pulmonary embolism, and sudden cardiac death (5). Abe et al., 1991 conducted a study on 151 lung cancer patients; 11.9% of these patients had myocardial involvement (6). Similarly, Cate et al., 1986 performed a retrospective analysis on 1046 patients and reported that new onset ECG changes highly suggest myocardial involvement in a clinically stable patient with malignancy (7). However, it is essential to remember that cardiac involvement is asymptomatic in most patients diagnosed with postmortem, precluding obtaining an ECG. TTE remains the diagnostic modality of choice, followed by conformation with additional imaging and biopsy.
The described patient had significant risk factors for lung cancer, including smoking and age. However, he had a normal screening CT scan done one year ago. Chest x-rays from the current and last admission showed nonspecific findings and failed to demonstrate lung mass. During his first “STEMI,” the patient presented with chest pain and ST-segment elevation with reciprocal changes and elevated cardiac biomarkers, revealing stable severe CAD with patent grafts. However, after the initial PCI, the patient’s condition improved, and other diagnostic studies did not suggest malignancy, so he was discharged. In his second admission with “STEMI,” he has a similar representation, leading to a coronary angiogram. The RCA was revascularized, assuming it must be the culprit lesion. A subsequent TTE showed the suspicion of cardiac mass, leading to a cardiac MRI and biopsy, revealing the diagnosis of invasive SCC of the lung metastasizing to the myocardium. The following pathways are identified for secondary cardiac metastasis: a) Hematogenous, b) lymphatic, c) transvenous, and d) direct extension. The hematogenous route leads to myocardial involvement. The lymphatic and direct extension leads to pericardial involvement (8). The described patient has myocardial involvement, indicating hematogenous metastasis. However, the patient had adjacent lymph node involvement but, surprisingly, no pericardial involvement.
The left upper lung mass remained undiagnosed despite multiple prior imaging modalities, including screening low-dose CT scans and numerous chest X-rays. A TTE in the presence of recurrent symptoms and persistent ST-segment elevation led to further investigations and diagnosis. In the described case, due to the presence of severe native CAD, it was difficult to exclude ischemic etiology. Patients with normal coronary arteries or mismatched ST elevation should undergo further investigations before discharge.