THE HISTO1,OGY O F SPONTANEOUS BONE TUMOURS IN MICE '
Y. C.PYBUS
ANn
E. W. MILLKK
(From the I . H . Burn Research Laboratory, Royal Victoria Infirniory, N ~ w r a s i l c - r ~ p o n - T y n e )
The gross pathology of bone tumours occurring spontaneously in an inbred
strain of mice has already been described (4). In general, these appear to
represent almost every possible phase of proliferative activity of the osteoblast;
they may occur in any bone, and several or even all the bones in an animal
FIG.I. HARDOSTEOMAOF ILIUM. X SS
This and other sections, except Fig. 6 , stained with Delafield's haematoxylin and eosin,
may be affected. I t is no exaggeration to say that every type of histologic
change may occasionally be illustrated from a single mouse.
The tumours from the first 106 sarcoma mice observed have been reexamined in an attempt to classify them according to the predominating type
of cell. A number of these animals had multiple lesions of different types.
Mouse 1688, for example, had a spindle-celled tumour of the tibia and an
ossifying tumour involving the spine and ribs. Bone and osteoid tissue were
the main features of tumours of the spine, ilium, and right femur of mouse
2706, which also had almost pure spindle-celled tumours of the rib and left
femur. Mouse 2810 had a giant-celled tumour of the tibia and an osteoma
of the spine. A number of similar examples might be quoted from the records.
Of the 118 tumours, 89 consisted principally of bone and osteoid tissue; 20
Received for publication Jan. 23, 1939.
54
HISTOLOGY O F SPONTANEOUS BONE TUMOURS I N MICE
55
F I G . 2 (LEFT). TRANSVERSE
SECTIOX
O F SPINE, SHOWING
LATERSTAGEOF
PROJECTIONS INTO THE SPINAL
CANAL(BONEAPPEARS
BLACK).
FIG.
OSTEOMATOSIS,
WITH
X C. 16
3 ( R I G I I T ) . LONGITUDINAL
SECTION
OF STERNUM,
SHOWING
GENERALISED
OSTEOMATOSIS
OF
M A N U B R I U M , WIT11 NORMAL
COSTAI.CARTILAGES
( B L A C K ) . X C. 16
were predominantly spindle-celled growths; 5 were mainly giant-celled tumours; and in only one was cartilage the principal feature, although it was
present in 5 tumours of other types. There were two tumours in which spindle
cells and osteoid tissue were present in equal amounts, and these must be
classed as mixed tumours (one of these also contained cartilage), while one
tumour was mainly round-celled, with some osteoid tissue and cartilage in addition. Giant cells were seen in 2 2 tumours altogether, and in only 10 tumours
were there no signs of osteogenesis. The accompanying illustrations show
the main types of tissue encountered.
( 1 ) Osteoma of the compact type was found growing from the long bones,
spine, pelvis, or skull. Fig. 1 shows a section of a slow-growing osteoma of
the pelvis. The hard lobulated bone has a somewhat rough lamellar arrangement. The vascular canals and lacunae are readily seen, while in the top
right-hand part of the photograph there is a small portion of normal ilium.
Some of the larger spaces elsewhere in the tumour contained normal marrow.
( 2 ) Osteoma of cancellous structure was the most common type of tumour
encountered and can be illustrated from almost any bone. I t may be entirely
intra-osseous, or may form a localised projecting tumour. More often multiple and diffuse, it passes through all phases to osteosarcoma.
Fig. 2 shows a transverse section of the spine and cauda equina from a paraplegic mouse. The whole body is irregular and becoming highly cellular; bone
and osteoid tissue are present. A projection into the spinal canal is seen compressing the cauda. The neural arch still contains normal marrow. A section of the manubrium sterni, shown in Fig. 3, is an example of generalised
cancellous osteomatosis. Costal cartilages are seen, while at the top left hand
corner the junction with the body is visible. No normal marrow is present.
F. C . PYBUS AND E. W. MILLER
( 3 ) Osteosarcoma: The dividing line between the osteoma and the osteosarcoma is very narrow, and it is often impossible to state where one ends and
the other begins. Frequently a hard osteoma will show a cancellous area, and
either may show in some region a proliferation passing into an infiltrating
cell mass.
Fig. 4 shows a section of a tibia; the bone is generally enlarged, its surface
roughened, and the interior is becoming occupied by rapidly proliferating
osteoblasts with a varying degree of bone formation. The dark patch at the
top of the photograph represents normal marrow, which elsewhere has been
replaced. A similar tumour is shown, under higher magnification, in Fig. 5.
This is from the tibia of a mouse which also had a bony metastasis in the lung;
58
F. C. PYBUS AND E. W. MILLER
there is a diffuse overgrowth of osteoblasts with some trabecular bone formation.
The mixed nature of some tumours is illustrated in Fig. 6. A cross-section
of a large tumour of the fore limb shows the humeral shaft, its marrow largely
replaced by osteogenic tissue, and the shaft partly surrounded by an osteoma.
From the osteoma and shaft springs a spindle-celled sarcoma, infiltrating
muscle and growing rapidly. In parts, the osteoma contains few cells and is
static, in others it is osteosarcomatous. The main portion of the tumour consists of spindle-cell sarcoma with no sign of osteogenesis, but in other regions
the cells are larger, rounder, and are associated with giant cells, while foci of
ossification also occur.
A spindle-cell sarcoma growing from a rib is shown in Fig. 7A. The re-
mains of the rib, with considerable alteration of the marrow (on the right),
are surrounded by spindle-celled sarcoma invading muscle, the muscle fibers
appearing as darker patches in the midst of the tumour. There is a gradual
change from osteoblasts to spindle cells, and no sign of osteogenesis. This
mouse had osteomata on the sternum, ilium, and spine, and a spindle-celled
sarcoma of the left femur. A higher magnification (Fig. 7B) of the spindlecelled tissue from a similar tumour shows spindle cells with large elongated
nuclei. This tumour and that shown in Fig. 3 were found in a mouse which
had extensive alterations throughout the skeleton and bony deposits in the
lungs. Every bone was examined microscopicaIly and all showed proliferative
changes.
No purely giant-celled tumour has been observed, but Fig. 8 shows an
approach to this type. The section was taken from a haemorrhagic tumour
of the tibia, in which there were irregular patches of osteogenesis, with many
osteoblastic and multinucleate cells. The latter are seen under the higher
magnification. The relatively small number of nuclei present in each should
be noted. The mouse bearing this tumour was a male of nine months and
had been receiving weekly injections of oestrone since the age of four
HISTOLOGY O F SPONTANEOUS BONE TUMOURS I N MICE
59
weeks. As far as our experiments go, such giant-celled tissue is a feature of
bone changes which appear in mice treated with oestrone (3, and unpublished
evidence).
Fig. 9 shows a chondro-osteo-sarcoma of the tibia. The tumour appeared at the upper end of the bone, and was the size of a small pea, hard,
and invading muscle. Histologically it was found to be composed of osteoid
tissue, with well formed hyaline cartilage, passing into spindle-cell sarcoma.
In the centre of the photograph is seen a portion of the shaft'of the tibia:
immediately to the left is a layer of osteoid growth passing through a layer of
chondroid tissue into spindle-cell sarcoma invading muscle; to the right of the
shaft, cartilage arises directly from the bone and passes through an intermediate type of tissue into spindle-cell sarccma.
Naturc of L ~ s i o n s :An examination of the bone lesions .in over 300 animals demonstrates every phase of activity of the osteoblasts, which appear to
be the malignant elements. One of the earliest phases consists of a trifling
localised bone hypertr,ophy with IittIe visible cellular activity. A continuation
of this process of localised proliferation of osteoblasts with concomitant bone
formation may produce various types of localised osteomata: on the one hand
the hard osteoma, often carrying normal marrow in its spaces, and with no
evidence of continuing osteoblastic activity; on the other, the cancellous type.
In the latter, cellular activity may produce cancellous tissue throughout one
bone, or the whole osseous system, or may form one or many localised tumours
on the surface of the bone. The degree of cellular activity in the cancellous
tumours is variable; in some it is trifling, in others considerable, while, in a
number,, cell growth may outstrip ossification and an osteosarco~naorbpure
spindle-celled sarcoma results.
In a few cases, small or large areas of giant-celled tissue are present, and
these also show a variable degree of osteogenesis. There are a few examples
60
F. C. PYBUS AND E. W. MILLER
of cartilage production, all types of cell being found: typical hyaline cartilage
may pass insensibly into less differentiated tissue and emerge as spindle-cell
sarcoma.
In certain cases, osteoblasts appear to give rise to spindle-cell tissue
directly; in.others only after a variable activity as osteogenic tissue.
Osteogenesis: The primary malignant cell in these bone tumours, as suggested above, is the osteoblast, which is stimulated to active proliferation and
differentiation. Osteogenesis is clearly seen in the formation of osteomata,
where it follows the course of normal membranous ossification, osteoid tissue
and true bone both occurring. I t is also found in the midst of purely spindlecelled growth and among giant-celled tissue. Occasionally a variety of cartilaginous ossification occurs, as shown in Fig. 9, which resembles that found
in tissue culture ( 1) , in which the presence of tissue intermediate between
true cartilage and bone has been described.
Giant Cells: The nature of the giant cells is not fully understood. As seen
in Fig. 8, they assume a variety of shapes. They are much larger than the
osteoblasts, and their cytoplasm is more acidophilic. They may have as many
as tweIve or fifteen nuclei, but usually smaller numbers, four or six, are more
common. In this they resemble the giant cells seen in human osteogenic sarcoma rather than those present in the benign giant-cell tumour of man (Geschickter and Copeland, 1936). They are of the type present in the bones of
young mice, which, as osteoclasts, assist in the destruction of cartilaginous
bone, but the malignant giant cell is larger and contains more nuclei.
Bone Marrow: The principal change which occurs in the medullary spaces
is their occupation by osteoblasts. As the illustrations show, the marrow cells
gradually disappear before the multiplying osteoblasts. In certain cases
greatly increased vascularisation has been observed, while in others patches
of degeneration are seen. A peculiar and rather frequent feature, of which
HISTOLOGY OF SPONTANEOUS BONE TUMOURS IN MICE
61
the relation to sarcoma is at present not fully understood, is a fibrous change
affecting part or all of the medullary s.paces and accompanied by bone hypertrophy; there is a distinct resemblance to. osteitis fibrosa, and the condition
occurs mainly in older mice (Fiq. 10).
Metastases: As has been noted ( 4 ) , metastases have been found in most
organs. They may be osseous or spindle-celled; even in the latter occasional
bone nodules occur, while in the former normal marrow has often been seen.
Metastases have been discovered before there was any evidence of extracsseous activity; no doubt, infiltration in the marrow readily leads to venous
emboli.
The histology of the various types of spontaneous bone tumours found in
the sarcoma strain of mice is described. The main classes are: hard osteoma,
cancellous osteoma, osteosarcoma, osteosarcoma with giant cells, and chondroosteo-sarcoma. Tumours in which bone and osteoid tissue predominate are
the most frequent. There is no fixed boundary between the classes: they
merge into one another, and one mouse may show all types in different lesions.
The primary malignant cell is believed to be the osteoblast, which is capable
of differentiating into all the types of cells concerned in bone development.
The changes which occur in the bone marrow are briefly mentioned.
NOTE:This work was carried out under a research grant from the British Empire Cancer
Campaign, to whom we would tender our grateful acknowledgments.
1. FELL,H.
B.: Proc. Roy. Soc., ser. B 112: 417, 1932-33.
2. GESCHICKTER,
C. F., AND COPELAND,
M. M.: Tumors of Bpne, pub. by Am. J. Cancer,
New York, 1936.
E. W.: Nature 142: 872, 1938.
3. PYBUS,F. C.,AND MILLER,
4. PYBUS,F. C., AND MILLER,E. W.: Am. J. Cancer 40: 47, 1940.