Mesenchymal chondrosarcoma is a form of malignant chondrosarcoma

Chondrosarcoma

Chondrosarcoma is a cancer composed of cells derived from transformed cells that produce cartilage. Chondrosarcoma is a member of a category of "soft tissue" malignancies known as sarcomas. About 30% of skeletal system cancers are chondrosarcomas...

. Unlike most chondrosarcomas, mesenchymal chondrosarcoma grows rapidly, tends to spread, and occurs more often in children and young adults than in older adults.
support: http://health.groups.yahoo.com/group/MesenchymalChondrosarcoma/

Type II collagen can help distinguish it from other tumors.