The changing face of central chondrosarcoma of bone. One UK-based orthopaedic oncology unit's experience of 33 years referrals

Abstract

Aim: To ascertain the changing incidence over time of the three commonest primary sarcomas of bone. Data obtained with particular reference to central chondrosarcoma from the annual referral rate to a large UK-based specialist orthopaedic oncology unit. To discuss how the "barnyard pen" analogy of cancers previously applied to certain commoner cancers can also be applicable to central chondrosarcoma (CS) of bone.

Materials and methods: A retrospective review was conducted of a computerised database identifying all central cartilage tumours (CCT) of bone, including enchondroma and CS subtypes, between 1985 and 2018. These were compared with the referrals of the other two commonest primary sarcomas of bone, osteosarcoma and Ewing sarcoma.

Results: There was a total of 1507 CS showing a 68% overall increase in annual referral rate/incidence over the study period. 68% cases were the borderline malignant lesions now known as atypical cartilaginous tumour (ACT). The annual referral rate/incidence of this entity increased by 194% over the 30 years. Whereas, the annual referral rate/incidence for osteosarcoma and Ewing sarcoma was static for the past 20 years.

Conclusion: The annual incidence of central CS of bone showed a marked increase over the 33-year period as compared with both osteosarcoma and Ewing sarcoma. This is especially in the ACT category and is thought to be due to the increased provision of MRI scanning flagging up a rise in incidental findings. The spectrum of CCTs from benign to highly malignant elegantly fits the "barn yard" pen analogy and could prove useful as an explanatory tool for patients and clinicians unfamiliar with these diseases.

Keywords: Atypical cartilage tumour (ACT); Chondrosarcoma; Enchondroma.

Fig. 1

Annual referral rate to the orthopaedic oncology unit of the 3 commonest primary sarcomas of bone expressed as a 5-year rolling average. Note data included from 1985 onward so first data points correspond to 1985.

Fig. 2

Annual referral rate to the orthopaedic oncology unit of all central CS compared with enchondroma expressed as a 5-year rolling average. Note data included from 1985 onward so first data points correspond to 1985.

Fig. 3

Annual referral rate to the orthopaedic oncology unit of all central CS broken down by subtype expressed as a 5-year rolling average. Note data included from 1985 onward so first data points correspond to 1985. Note annual average for dedifferentiated CS prior to 1995 < 1. ACT = atypical cartilage tumour. Gr II = Grade 2, Gr III = Grade 3 and Dedifferentiated CS.

Fig. 4

Schematic applying the “barnyard pen” (BP) analogy of cancers to the spectrum of central CS. 1 represents the most aggressive type of CS, dedifferentiated, with a high metastatic potential symbolised by the bird. The bird can fly out of the pen at any time irrespective of the height of the fence. 2 represents the locally aggressive CS, grade 2 and 3, with intermediate metastatic potential symbolised by the rabbit. The confinement of the rabbit within the BP will depend on prompt diagnosis and treatment. Failure to do so may result in the rabbit escaping over the fence. 3 represents the most indolent CS (ACT – atypical cartilage tumour) symbolised by the turtle. These will remain confined within the pen notwithstanding the height of the fence.