Skeletal muscle metastases from papillary and follicular thyroid carcinomas: An extensive review of the literature

Skeletal muscle metastasis of papillary or follicular thyroid cancer (PTC/FTC) is a rare finding; only 11 cases of skeletal muscle PTC or FTC metastasis have been included in medical literature reviews. The aim of this study was to identify all published cases of PTC and FTC muscle metastases and derive the true incidence of this malignancy. The probability of detecting the skeletal muscle metastasis of PTC and FTC was calculated based on epidemiological data. Databases of scientific literature on the Internet were searched for articles using relevant key words. The analysis of epidemiological data calculated the probability of detecting skeletal muscle lesions of this type as approximately zero. The literature search revealed 44 published international papers, reporting 58 cases of PTC or FTC skeletal muscle metastasis in 45 patients over 110 years, from 1907 to 2017. The most frequent PTC/FTC metastatic muscle was the gluteus. The majority of cases of muscle metastasis were caused by PTC, and metastatic tumors in the skeletal muscle negatively impacted the survival of patients with PTC or FTC.