Secondary peripheral chondrosarcoma, grades 2 and 3

Staging is according to bone sarcoma protocols (see TNM staging of tumors of bone). See also the information on staging in the section Bone tumors: Introduction.

Whereas in secondary peripheral ACT/CS1, EXT-mutant cells and EXT-wildtype cells coexist, in high-grade secondary peripheral chondrosarcoma, the EXT-wildtype cells predominate. Similar to grade 2 and 3 central chondrosarcoma, these chondrosarcomas display chromosomal instability and a complex karyotype that increases with increasing histological grade, probably caused by alterations in the p53 and RB1 pathways.

These lesions are translucent lobular bluish-white tumors in which there may be areas with myxoid material and cystic changes. The stalk of the pre-existing osteochondroma might still be recognized; the cap size exceeds 2 cm.

Grade 2 and 3 secondary peripheral chondrosarcomas are lobular cartilaginous matrix–producing tumors that are morphologically identical to grade 2 and 3 central chondrosarcomas. Sometimes areas of endochondral ossification suggestive of pre-existing osteochondroma can be seen. Nuclear pleomorphism and mitoses are often easily seen. At the periphery of the neoplastic cartilaginous lobules, spindle cell changes may occur. Coarse and irregular calcification, binucleated cells, cystic change, and necrosis can be observed.

Immunohistochemistry
These tumours can be positive for S100.

Grading
Criteria for histological grading are identical to those for grade 2 and 3 central chondrosarcoma.

Differential diagnosis
Periosteal osteosarcoma is included in the differential diagnosis. Peripheral chondrosarcoma is separated from central chondrosarcoma based on its location at the surface of the bone.

Not clinically relevant.

Local recurrences can occur, generally related to incomplete excision. The majority of patients who die of their disease have local recurrence.

Molecular analysis is rarely needed for diagnosis. Mutations in IDH1, IDH2, and NRAS are absent.

Essential: chondrosarcoma arising in a pre-existing osteochondroma or with evidence of the stalk of a precursor osteochondroma; cartilage cap exceeds 2 cm; mitoses and nuclear pleomorphism are present.