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WHO Classification
of Bone Tumours
Primary neoplasms of the skeleton are rare, amounting to
only 0.2% of the overall human tumour burden. However,
children are frequently affected and the aetiology is
largely unknown.
Significant progress has been made in the histological
and genetic typing of bone tumours. Furthermore,
advances in combined surgical and chemotherapy
havelead to a significant increase in survival rates even
for highly malignant neoplasms, including osteosarcoma
and Ewing sarcoma.
Several bone tumours occur in the setting of inherited
tumour syndromes, but their histology differs little from
the respective sporadic counterparts.
WHO classification of bone tumours
CARTILAGE TUMOURS
Osteochondroma
9210/0*
GIANT CELL TUMOUR
Giant cell tumour
9250/1
Chondroma
9220/0
Malignancy in giant cell tumour
9250/3
Enchondroma
9220/0
Periosteal chondroma
9221/0
Multiple chondromatosis
9220/1
NOTOCHORDAL TUMOURS
Chordoma
9370/3
Chondromyxoid fibroma
9241/0
Chondrosarcoma
9220/3
Central, primary, and secondary
9220/3
VASCULAR TUMOURS
Haemangioma
9120/0
Dedifferentiated
9243/3
Angiosarcoma
9120/3
Mesenchymal
9240/3
Clear cell
9242/3
SMOOTH MUSCLE TUMOURS
Leiomyoma
OSTEOGENIC TUMOURS
Osteoid osteoma
Leiomyosarcoma
8890/0
9191/0
Osteoblastoma
9200/0
Osteosarcoma
9180/3
LIPOGENIC TUMOURS
Lipoma
Conventional
9180/3
8850/0
chondroblastic
9181/3
Liposarcoma
8850/3
fibroblastic
9182/3
osteoblastic
9180/3
Telangiectatic
9183/3
NEURAL TUMOURS
Neurilemmoma
Small cell
9185/3
9560/0
Low grade central
9187/3
Secondary
9180/3
Parosteal
9192/3
MISCELLANEOUS TUMOURS
Adamantinoma
Periosteal
9193/3
9261/3
High grade surface
9194/3
Metastatic malignancy
FIBROGENIC TUMOURS
Desmoplastic fibroma
8823/0
MISCELLANEOUS LESIONS
Aneurysmal bone cyst
Simple cyst
Fibrous dysplasia
Osteofibrous dysplasia
Langerhans cell histiocytosis
Fibrosarcoma
8810/3
FIBROHISTIOCYTIC TUMOURS
Benign fibrous histiocytoma
9751/1
8830/0
Erdheim-Chester disease
Chest wall hamartoma
Malignant fibrous histiocytoma
8830/3
EWING SARCOMA/PRIMITIVE
NEUROECTODERMAL TUMOUR
Ewing sarcoma
JOINT LESIONS
Synovial chondromatosis
9220/0
9260/3
HAEMATOPOIETIC TUMOURS
Plasma cell myeloma
9732/3
___________________________________________________________
*
Morphology code of the International Classification of Diseases
for Oncology (ICD-O) {726} and the Systematized Nomenclature
of Medicine (http://snomed.org). Behaviour is coded /0 for benign tumours,
/1 for unspecified, borderline or uncertain behaviour, /2 for in situ carcino-
mas and grade III intraepithelial neoplasia, and /3 for malignant tumours.
226
Chondroblastoma
9230/0
Peripheral
9221/3
8890/3
Malignant lymphoma, NOS
9590/3
WHO classification of tumours of
bone: Introduction
H.D. Dorfman
D. Vanel
B. Czerniak
Y.K. Park
R. Kotz
K.K. Unni
Among the wide array of human neo-
plasms, primary tumours of bone are rel-
atively uncommon. Not only has this con-
tributed to the paucity of meaningful and
useful data about the relative frequency
and incidence rates of the various sub-
types of bone tumours, but it also
explains our rudimentary understanding
of risk factors.
Little information is available concerning
the aetiology and epidemiologic features
of benign bone tumours since most pub-
lished statistical studies have dealt with
bone sarcomas. The benign lesions will
be considered from the epidemiologic
and aetiologic standpoint under the indi-
vidual chapter headings, where they are
known.
malignant fibrous histiocytoma, account-
ing for a marked decline in the frequency
of the former diagnostic category.
lar skeleton has a tendency to decrease
with age. In patients older than fifty,
osteosarcoma of the extremity bones
makes up only 50 % of cases. In this
group, the pelvis and craniofacial bones
each account for about 20 % of the
cases. The incidence rate of extremity
bone involvement for patients older than
50 is approximately one third of that for
persons in the younger age groups.
Chondrosarcomas have age-specific
incidence rates showing a gradual
increase up to age 75. The age adjusted
rates show little difference by sex and
race. More than 50 % of chondrosarco-
mas occur in the long bones of the
extremities. The other major sites of
involvement are the pelvis and ribs. The
latter site and the sternum are high risk
sites for malignant cartilage tumours.
Ewing sarcomahas epidemiological fea-
tures similar to those of osteosarcoma,
but while osteosarcomas tend to occur in
the metaphyseal areas of long bones of
skeletally immature patients, particularly
in the knee region, Ewing sarcoma tends
to arise in the diaphysis. The age-specif-
ic relative frequency and incidence mir-
Age and site distribution
The age-specific frequencies and inci-
dence rates of bone sarcomas as a
group are clearly bimodal. The first well
defined peak occurs during the second
decade of life, while the second occurs
in patients older than sixty. The risk of
development of bone sarcomas during
the second decade of life is close to that
of the older than 60 population, but there
are more cases in the second decade.
The bimodal age-specific incidence rate
pattern of bone sarcomas is clearly dif-
ferent from that of soft tissue sarcomas,
which shows a gradual increase of inci-
dence with age.
Osteosarcoma occurs predominantly in
patients younger than age twenty, and in
this group 80% occur in long bones of
the extremities. In this age group, a small
proportion of cases involve other parts of
the skeleton, such as craniofacial bones,
the spine, and pelvis. The clear predilec-
tion of osteosarcoma for the appendicu-
Incidence
In general, bone sarcomas account for
only 0.2% of all neoplasms for which
data were obtained in one large series
(SEER) {1789}. Comparison of the inci-
dence rate of bone sarcomas with that of
the closely related group of soft tissue
sarcomas indicates that osseous neo-
plasms occur at a rate approximately
one tenth that of their soft tissue counter-
parts {537,946,1304}.
In North America and Europe, the inci-
dence rate for bone sarcomas in males is
approximately 0.8 new cases per 100,000
population and year. Somewhat higher
incidence rates have been observed for
males in Argentina and Brazil (1.5-2) and
Israel (1.4) {1665}. Cancer registry data
with histological stratification indicate that
osteosarcoma is the most common pri-
mary malignant tumour of bone, account-
ing for approximately 35 percent of
cases, followed by chondrosarcoma
(25%), and Ewing sarcoma (16%). In
countries and regions with higher inci-
dence rates, the relative fraction of osteo-
sarcomas appears to be larger.
Chordomas and malignant fibrous histio-
cytoma are much less frequent, constitut-
ing approximately 8 and 5% of bone
tumours, respectively. In recent years, the
diagnosis of fibrosarcoma primary in
bone has largely been replaced by that of
Fig. B.1
Age-specific incidence rates by histological subtype, all races, both sexes, SEER data, 1973-1987. MFH,
malignant fibrous histiocytoma and fibrosarcoma.
227
Relative frequencies of bone sarcomas by histological type, sex, and race: SEER data 1973-1987
es of bone malignancies, other expo-
sures and conditions have been suspect-
ed (e.g. chromium, nickel, cobalt, alu-
minum, titanium, methyl-methacrylate,
and polyethyelene) but not unequivocally
confirmed. Recently attention has been
focused on a small number of reported
cases of bone sarcomas arising in asso-
ciation with implanted metallic hardware
and joint prostheses {788, 879,
1083,1683,2225}. However, the epidemi-
ological evidence for a causitive role is
still limited or inconclusive {6}. Future
molecular epidemiological studies in
patients who have undergone ortho-
paedic implantation of metallic and other
foreign materials may provide clues to
the pathogenetic mechanisms underlying
malignant transformation in bone.
Total
White
Black
Histological type
No.
%
No.
%
No.
%
Osteosarcoma
922
35.1
743
32.6
106
57.9
Chondrosarcoma
677
25.8
615
27.0
35
19.1
Ewing sarcoma
420
16.0
392
17.3
7
3.8
Chordoma
221
8.4
200
8.8
4
2.2
Malignant fibrous histiocytoma 149
5.7
125
5.5
13
7.1
Angiosarcoma
36
1.4
35
1.5
1
0.5
Unspecified
32
1.2
27
1.2
3
1.6
Other
170
6.4
139
6.1
14
7.8
Total
2627
100.0
2276
100.0
183
100.0
____________
From H. Dorfman & B. Czerniak {537}.
Clinical features
The clinical features of bone tumours are
non-specific, therefore a long period of
time may elapse until the tumour is diag-
nosed. Pain, swelling and general discom-
fort are the cardinal symptoms that lead to
the diagnosis of bone tumours. However,
limited mobility and spontaneous fracture
may also be important features.
ror those of osteosarcoma with the major
peak occurring during the second
decade of life. Although there is a rapid
decrease in incidence after age 20,
cases are seen in all age groups. Unlike
osteosarcoma, Ewing sarcoma is report-
ed to occur almost exclusively in the
white population.
lesions that predispose to malignant
transformation. Others are benign neo-
plasms that can be the source of a malig-
nant neoplastic process. The likelihood of
discovering such associated lesions can
be facilitated by attention to clinicopatho-
logical correlation of all available data
before arriving at a diagnosis. In bone,
the inclusion of radiographic imaging
data in the diagnostic process offers a
unique opportunity to discover clues to
causal relationships that may not be
reflected in histological patterns or in
other laboratory data. This is especially
true when serial radiographs are avail-
able for review.
Paget disease, radiation injury, and some
of the more common benign cartilaginous
dysplasias are the most clearly estab-
lished precancerous conditions. Both
osteosarcoma and malignant fibrous his-
tiocytoma have been linked to pre-exist-
ing condition of bone such as Paget dis-
ease, radiation damage, bone infarction,
fibrous dysplasia, chronic osteomyelitis,
and some genetically determined syn-
dromes {25,132,390,797,867,989,1042,
2263}. The relative rarity of malignant
transformation in fibrous dysplasia,
osteomyelitis, bone cysts, osteogenesis
imperfecta, and bone infarction places
these conditions in a separate category
{540,725,760, 892,1471,2122}.
Precursor lesions
Although the majority of primary bone
malignancies arise do novo, it is increas-
ingly apparent that some develop in
association with recognizable precursors.
Some of these represent non-neoplastic
Precursors of malignancy in bone
High Risk
Ollier disease (Enchondromatosis)
and Maffucci syndrome
Familial retinoblastoma syndrome
Rothmund-Thomson syndrome (RTS)
Fig. B.2
Osteochondroma. Hard, smooth, nodular
swelling of the distal femur, skin and soft tissues are
easily movable and the knee joint is freely mobile.
Moderate Risk
Multiple osteochondromas
Polyostotic Paget disease
Radiation osteitis
Low Risk
Fibrous dysplasia
Bone infarct
Chronic osteomyelitis
Metallic and polyethylene implants
Osteogenesis imperfecta
Giant cell tumour
Osteoblastoma and chondroblastoma
Aetiology
While radiation and chronic inflammatory
states are established, though rare caus-
Fig. B.3
Osteosarcoma, causing swelling in the dis-
tal femur. Soft tissues poorly movable, consistency
ranging from tough to hard, hyperthermia of the skin
and marked veins.
228
additional complaints. Swelling is only
observed if there is an extraosseous part of
the tumour or the bone is expanded by the
tumourous process. In malignant tumours,
swelling develops more rapidly. A descrip-
tion of consistency is important e.g. hard,
coarse, tightly elastic or soft. Metric data
concerning swelling (in centimeters)
should be given; ultrasonic examination
may be helpful to establish objective sizes.
In advanced stages, tumour swelling may
also cause skin changes, including tensed
shining skin with prominent veins, livid
colouring, hyperthermia, as well as stria-
tion of the skin and eventually, ulceration.
The mobility of the skin, subcutis and mus-
culature above the tumour should also be
assessed. The less the mobility, the more
likely is this factor a criterion of malignancy.
fibromas. In cases of malignant bone
tumours, fracture is a rather rare primary
event, as it usually occurs in advanced
stages of osteolytic malignant tumours
and the patient will have experienced
pain and tumour growth prior to it.
General symptoms
These mainly consist of fever, exhaustion
and loss of weight. They are late signs in
malignant tumours, and will be absent in
nearly all cases of benign bone lesions.
Imaging of bone tumours
Diagnosis
Combining both radiological and histo-
logical criteria is most appropriate.
Based on clinical and radiological signs,
one should first diagnose benign lesions
for which a subsequent biopsy may not
be necessary:
> Metaphyseal fibrous defect
> Fibrous dysplasia
> Osteochondroma
> Enchondroma
> Simple bone cyst
> Vertebral haemangioma
Age is useful information: before age of
5, a malignant tumour is often metastatic
neuroblastoma; between 5 and 15 years
old, osteosarcoma or Ewing sarcoma;
and after 40 years, metastasis or myelo-
ma.
The first step is to determine tumour
aggressiveness by conventional radiolo-
gy. Important parameters include tumour
Fig. B.4
Ewing sarcoma of the proximal humerus,
presenting as tightly elastic, tense, ulcerated
lesion with shining skin, on a grey-white back-
ground. Note the marked veins and skin striation.
Limitation of movement
Mobility may be limited in cases of
lesions close to the joint, in tumours such
as osteoblastoma, chrondroblastoma,
giant cell tumours and all types of sarco-
mas. Occasionally it is not the tumour but
reactive synovitis in the joint, especially
in chondroblastoma, that causes limita-
tion of movement and masks the true
diagnosis.
Pain
Pain is the first and most common symp-
tom in nearly all malignant bone tumours
{388,429,1025,1159,1254}. If a sponta-
neous fracture does not occur, the symp-
toms usually commence slowly. Initially
the patient has tearing neuralgia-like
pain, which may also be interpreted as
"rheumatic pain". Although the symptoms
may initially occur intermittently and only
at rest, the pain might subsequently
become more intense, disturb sleep at
night, spread into the adjacent joint and
is frequently misinterpreted as arthritis or
as a post-traumatic phenomenon.
A further intensification of pain is experi-
enced as a persistent and piercing pain.
During disease progression, the pain
becomes excruciating and intolerable,
requiring opiate treatment.
In case of pressure on nerve trunks or
nerve plexuses, the patient may experi-
ence radiating pain. A specific kind of
pain occurs when the tumour is located
in the spine and causes radicular or
spinal compression symptoms with
paralysis.
Pathologic fracture
Fracture is diagnosed early, as it causes
the patient to seek attention immediately.
It may occur with no prior symptoms at
all, as is frequently the case in juvenile
cysts and in some non-ossifying bone
Swelling
The second most important symptom in
bone tumours is swelling, which may fre-
quently be of very long duration, especial-
ly in benign neoplasms, and cause no
Fig. B.5
The choice of the imaging technique.
229
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