MONDO_0002401 (malignant tenosynovial giant cell tumor) is an uncommon malignant tumor arising from the tendon sheath. Morphologically, it is characterized by the presence of a cellular infiltrate reminiscent of a giant cell tumor with prominent malignant characteristics. Recurrent giant cell tumors with a sarcomatous dedifferentiation are included in this category as well. Also known as: giant cell tumor of tendon sheath, malignant, giant cell tumour of tendon sheath, malignant, malignant giant cell neoplasm of tendon sheath, malignant giant cell neoplasm of the tendon sheath, malignant giant cell tumor of tendon sheath, malignant giant cell tumor of the tendon sheath, malignant giant cell tumour of tendon sheath, malignant giant cell tumour of the tendon sheath.