A locally aggressive, low-grade chondrosarcoma arising in the medulla of bone. Tumors in the appendicular skeleton are called central atypical cartilaginous tumors and tumors in the axial skeleton are called central chondrosarcomas, grade 1. Tumors arising in the medulla of the bone without a benign precursor are called primary central atypical cartilaginous tumors/chondrosarcomas, grade 1. Tumors arising in the medulla of the bone in association with a pre-existing enchondroma are called secondary central atypical cartilaginous tumors/chondrosarcomas, grade 1. [from NCI]