Anaplastic transformation of metastatic papillary thyroid carcinoma at shoulder mimicking soft tissue sarcoma.

A 52-year-old woman presented with fracture upper end of the left humerus after trivial trauma and aspiration cytology from the lytic lesion in the upper humerus seen on X-ray revealed a metastatic papillary carcinoma from the thyroid. Total thyroidectomy confirmed the papillary carcinoma thyroid. Post-operatively, she was given radioactive iodine (I-131) ablation therapy for 8 years and was asymptomatic during this period; however, for the last 1 year, she has been complaining of swelling in the shoulder, which did not respond to palliative radiotherapy and rapidly increased in size. Disarticulation of the shoulder joint was performed, which showed anaplastic carcinoma on histopathological examination. Anaplastic transformation of papillary carcinoma at the metastatic sites is well documented in the literature and is rare. However, the same has not been reported at the shoulder and from India before. Although soft tissue sarcomas are most common at this site, however, the possibility of anaplastic transformation should be kept in the differential diagnosis of rapidly enlarging painful mass in a known case of metastatic thyroid carcinoma to prevent misdiagnosis.