Most bone tumours encountered in clinical practice are secondary forms (i.e. spread - metastases - from a separate primary cancer that started elsewhere), and it is incorrect to refer to these as ‘bone cancer’.
Doctors use the term bone tumours to refer to tumours which arise in the bone from the start (primary bone tumours), rather than those which are spread from a cancer that has originated elsewhere.
This point is of importance as the methods and data outlined in this section do not apply to secondary bone cancers/metastases.
Incidence of bone tumours
Most bone tumours encountered in clinical practice are secondary (i.e. metastases from primary cancer that started elsewhere), and it is a layman’s misnomer to refer to these as ‘bone cancer’. The doctor reserves this term to those tumours of bone which arise in the bone ab initio. The point is of importance as the methods, and data outlined below do not apply to bone tumours as secondary/metastases.
Primary bone tumours include osteogenic sarcoma (arising from the true bone forming cell) Ewing’s sarcoma (arising from a primitive pluripotential cell), chondrosarcoma (arising from the cartilage forming cell line) and other rare forms of sarcoma (e.g. malignant fibrous histiocytoma).
Primary bone lymphoma will not be considered here, nor the sarcomas which are more commonly associated with soft tissues such as bone and connective tissue.
Osteogenic sarcoma occurs with two peak incidences in life. The first is in adolescence (when the bones are actively growing) and the second is in late life when it is not infrequently associated with Paget’s disease of bone. Exposure to radiation predisposes to the later development of osteogenic sarcoma, and some patients with familial syndromes (par excellence those with hereditary retinoblastoma – but see introductory remarks concerning soft tissue sarcomas for others) are predisposed.
Ewing’s sarcoma tends to present in youth and is very unusual over the age of 40 years.
Both osteogenic sarcoma and Ewing's sarcoma are less common in people of African extraction.
Chondrosarcomas, whilst certainly afflicting the young, are overall more common in later life again two peaks of age incidence.
Symptoms of bone tumours
The classical presentation to the doctor is with a painful swelling arising from the affected bone. Occasionally the patient may present with a fracture through the involved bone.
Whereas osteogenic sarcoma tends to involve the ends of long bones, Ewing’s tends to arise in the mid portions of long bones (the term long bones refer to limb bones such as the femur or humerus etc…).
Treatment of bone tumours
Treatment of early bone tumours depends heavily on the expert input of several groups of experts.
Where the tumours can be surgically removed, then expert orthopaedic input is required and any operation may be attended by the immediate placement of a prosthetic implant (see figure).
However, it may not be best to go straight to operation. Often and for both Ewing's sarcoma and osteogenic sarcoma - for which there is no evidence of spread, primary therapy is with chemotherapy. The drugs are given intravenously, which implies that they circulate around the body and not only shrink down the original/primary tumour but also knock out early spread of microscopic cells that could otherwise later clone in other body areas to become established metastases.
For both osteogenic sarcoma and Ewing's sarcoma, a several month programme of chemotherapy precedes any surgery. In many cases, cancers that had grown beyond the confines of the bone can be shrunk back into the bone by such chemotherapy and the subsequent operation then has a better chance of obtaining clear margins (i.e getting that highly desirable buffer of uninvolved tissue between the cancer and the cut margin). Any cancer cells (that might have travelled away from the primary bone cancer) are also attacked at an early stage of their development (and hopefully annihilated).
The operation is often able (as shown in the figure) to place a prosthesis where the bone tumour was, so that the patient has a return to function of the limb. However, sometimes, the tumour is just too extensive and large to allow the approaches just outlined, and the patient may have to undergo a limb amputation.
Radiotherapy has a selected place when it is not possible to resect (cut out) the tumour completely, for example in the vertebral column (where it is less easy to fully resect the tumour).