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We describe a patient with both gastric adenocarcinoma and metastatic squamous cell carcinoma (SCC) of unknown primary site. The possibility of a single malignant clonal process as opposed to differing primaries was supported by the finding of both histologies exhibiting high microsatellite instability. Despite evidence of tumor microsatellite instability, the patient's disease process did not respond to immune checkpoint inhibition. Our pursuit of whole-exome sequencing and comparing the single-nucleotide variant profiles of both tumors supported a single clonal process with the development of significant intratumoral heterogeneity. High intratumoral heterogeneity has posed a challenge to precision medicine approaches, but we also provide a review of the literature of this phenomenon mediating resistance to immunotherapy strategies. [ABSTRACT FROM AUTHOR]

Background Cardiac tumours are typically secondary in nature, and the most common malignancies metastasizing to the heart are cancers of the lung, breast, oesophagus, melanoma, and lymphoma. We present a unique case of squamous cell carcinoma of the tongue, metastasizing to the heart and manifesting with ST elevation in the inferior-leads on electrocardiogram (ECG). Case summary A 25-year-old woman was initially diagnosed with squamous cell carcinoma of the tongue at the age of 23 and treated with hemi-glossectomy with clear-margins. Sixteen months later, the tumour recurred in the oropharynx and the left upper lobe of the lung. She was treated with chemotherapy; however, the tumour progressed. Thus, she was initiated on immunotherapy and radiation therapy. One month later, she presented with chest pain. Electrocardiogram revealed ST elevation in the inferior-leads. Troponin-I was elevated. Transthoracic echocardiogram revealed focal areas of thickening within the left and right ventricular myocardium with associated hypokinesis. These findings suggested ECG changes were likely secondary to infiltrative metastases and not acute-coronary-syndrome. Cardiac magnetic resonance imaging showed infiltrative masses with increased T2-signal and heterogeneous enhancement on perfusion and delayed enhancement sequences. Imaging also demonstrated numerous extra-cardiac metastases. She was treated with analgesics and discharged to home hospice. Discussion Head and neck cancers are a rare cause of cardiac metastasis. ST elevation and troponin release are thought to be due to tumour extension into the myocardium. Cardiac metastases usually present in patients with advanced widespread malignancy. In a cancer patient with cardiac symptoms or ECG changes, it is important to consider a broad differential diagnosis and entertain the possibility of cardiac metastasis. [ABSTRACT FROM AUTHOR]