Abstract
Intramuscular myxoma (IMM) as a rare soft-tissue tumor arising from the muscles is completely benign. When IMM accompanies malignance, it may be misdiagnosed as muscle metastasis, and for this extremely rare concurrence, the subsequent treatment would vary accordingly. The current study presents, to the best of our knowledge, the first case of non-small cell lung cancer (NSCLC) concomitant with IMM mimicking skeletal muscle metastasis. A 64-year-old female was hospitalized with a history of chest discomfort and right lumbar pain that had persisted for four months. The computed tomography scan showed a lesion in the left upper lobe of the lung and the right psoas, respectively. Serum biomarkers for NSCLC were abnormal. A presumptive clinical diagnosis was compatible with left NSCLC and right psoas muscle metastasis (cT2aN3M1b, stage IV). Stage IV lung cancer would receive palliative treatment. However, the final diagnosis of synchronous left lung squamous cell carcinoma (cT2aN3M0, stage IIIB) and IMM in the right psoas was confirmed by biopsy. The patient therefore underwent definitive chemoradiotherapy for lung carcinoma, and conservative treatment, including analgesics, for IMM. The diagnosis process for a malignant neoplasm concomitant with IMM is not straightforward due to a lack of clinical experience, and it significantly affects the tumor staging and subsequent treatment strategy. The present case suggests that IMM should be included in the differential diagnosis when an abnormal intramuscular lesion concomitant with malignancy is identified. The value of histopathological diagnosis prior to definitive treatment also requires highlighting.