Osteosarcoma
Osteosarcoma describes a sarcomatous
lesion with characteristic bony elements. There are at least 9 different types of
osteosarcoma. In this chapter we will
discuss only the following: classic/intramedullary, periosteal, parosteal,
secondary, and telangectatic.
Classic or high-grade intramedullary
osteosarcoma is the most common and predominately affects males in 2nd and 3rd decade. It involves the metaphyseal region of bone
and is usually located about the knee
(50%) and proximal humerus. The hindfoot can also be affected. Symptoms of osteosarcoma often include pain that precedes any palpable mass,
and an overlying nevus that expands is not uncommonly found. Ten to twenty percent of patients will have
pulmonary metastases on presentation and as many as 90% will have micrometastases.
The p53 gene has been
implicated in the formation of osteosarcoma.
Radiographic appearance shows a permeative, lytic lesion of metaphyseal
bone and the classic “codman’s triangle”
is formed as the tumor pushes thru the cortex and raises the periosteum (Figure
#14). The body then fills this void
with bone creating a triangular structure.
As many as 25% of presentations can have “skip lesions” or disease further along the bone than the original
presenting lesion. Histologically,
the unifying factor includes the presence
of osteoid in a bed of pleiomorphic spindle cells that appear frankly
malignant. A MRI should be obtained
to delineate the borders of the lesion and involvement of surrounding structures
such as neurovascular bundles and muscle.
|
Figure #14
Osteosarcoma
of the distal femoral metaphysis. |
Treatment of these lesions with
simple amputation is historically grim with a survival of 10-20%
long-term. This invariably was due to
the presence of untreated micrometastases, and the picture has changed with the
introduction of chemotherapeutic agents.
Current regimens achieve 60-70%
long-term survival and include pre-resection multiagent chemotherapy termed
“adjuvant” chemotherapy (currently
includes methotrexate, doxorubicin and ifosfamide) followed by re-staging,
resection, and follow-up chemotherapy for 6-12 months. Following pre-resection chemotherapy, the best prognosticator is tumor necrosis. Fifty percent of lesions will show rates of necrosis over 90%, which are
associated with 85% 5-year survival.
Secondary osteosarcoma can arise
within the setting of multiple conditions that include: Paget’s Disease,
osteoblastoma, fibrous dysplasia, giant cell tumor, bone infarct, and chronic
osteomyelitis. Patients tend to be
older or elderly and the lesions involve the proximal humerus followed by the
pelvis and femur. Classically, this
disease presents with the new onset of pain overlying the usual dull achy pain
associated with the primary disease (i.e. Paget’s). The new pain signals the presence of a new lytic lesion. The 5-year survival for this disease is 8%
and most patients are too old to successfully tolerate chemotherapy.
Periosteal osteosarcoma is a
low-intermediate grade variant that affects primarily the diaphysis of long
bones and accounts for only 2% of osteosarcomas. It strikes mostly women in the 2nd decade of
life. While the diaphyseal location
means limb and joint salvage are often possible there is a high rate of
metastasis and 25% will die in the first two to three years. The lesion forms just under the periosteum
on the cortical surface and lifts the periosteum causing vigorous
neo-osteogenesis. On plain film
radiographs, this lesion is described as a sunburst-like lesion with a
saucerized cortical depression. It has
been likened to a “meteorite impact”
with a lytic crater and a large amount of surrounding bone emulating impact
debris. The differential includes
aneurysmal bone cyst (ABC) and periosteal chondroma. Adjuvant chemotherapy, wide resection and maintenance
chemotherapy are mainstays of treatment and this variant carries a slightly
better prognosis than classic osteosarcoma.
Parosteal Osteosarcoma represents a low-grade variant that predominates in women. The lesions present mostly on the posterior aspect of the distal femur at the metaphyseal segment of bone and do not involve the medullary cavity (Figure #15).
|
Figure # 15
parosteal osteosarcoma
of the distal femur. |
Symptoms
are generally absent other than a painless mass. Radiographs show a lobulated, ossified mass
that appears “stuck on” to the
cortex. Histologically these lesions
show spindle cells with well-developed trabeculae and osteoblasts. Treatment includes wide surgical resection
and small lesions can simply be removed with a single cortex. XRT and chemotherapy do not have a role unless
dedifferentiation has occurred
within the lesion (found about one sixth of the time). Five-year survival rates are above 85% though lesions need to be followed
for at least 10 years following
resection as recurrence and dedifferentiation to high-grade sarcoma is possible
and carries a poor prognosis.
Telangectatic Osteosarcoma, also
known as hemorrhagic osteosarcoma, represents a high-grade variant that strikes in the second to third decade. This aggressive lesion has the same
distribution as classic osteosarcoma, but advances rapidly and puts the patient
at significant risk for pathologic
fracture. Radiographically, this
lesion is lytic and highly destructive. It has the same appearance as an aneurysmal bone cyst (ABC) and the two are
easily confused. Histologically, the
lesion appears as a hemorrhagic pool of blood with highly malignant appearing
stromal cells interspersed. Treatment and prognosis are similar to high-grade
osteosarcoma. However, the presence of pathologic fracture precludes limb salvage
and pushes limb amputation into the forefront as the procedure of choice. Therefore, new lesions need strict protection while undergoing
adjuvant chemotherapy.
