Abstract
BACKGROUND: Pleomorphic rhabdomyosarcoma (PRMS) is a highly malignant soft tissue sarcoma that typically occurs in the soft tissues of the extremities. PRMS arising in the thyroid is extremely uncommon and can be difficult to distinguish from sarcomatoid transformation of anaplastic thyroid carcinoma. CASE PRESENTATION: A 58-year-old male presented with a rapidly enlarging left thyroid mass accompanied by dysphagia, dyspnea, and hoarseness. Imaging revealed a 7.0 cm cystic-solid mass invading the esophagus and cervical lymphadenopathy. Core needle biopsy (CNB) confirmed pleomorphic rhabdomyosarcoma through immunohistochemical staining (desmin+/myoD1+/myogenin+) and exclusion of epithelial 24 markers (TTF-1-/CK-). Genetic analysis identified the TP53 mutation, without BRAF V600E or 25 RET/PTC rearrangements. The tumor was surgically resected via total thyroidectomy and central lymph node dissection, followed by adjuvant radiotherapy and chemotherapy per soft tissue sarcoma treatment guidelines. The disease recurred at 24 months postoperatively, leading to loss of follow-up. CONCLUSIONS: Under specific circumstances, CNB can provide an effective diagnostic approach for thyroid tumors. Moreover, in this case, we identified a novel TP53 intronic mutation that may drive the development of thyroid PRMS.