Giant cell tumor of bone derives from cellular elements of the bone marrow.
Both the mononuclear and giant cells of the tumor show evidence of histiocytic
differentiation. The giant cells apparently originate by fusion of the mononuclear
cells. The mononuclear cells are the principal cells of this lesion. Multinucleated
giant cells are present in many tumors, thus their presence in lesional tissue
does not necessarily establish the diagnosis of giant cell tumor.
The incidence of giant cell tumor peaks during the third decade of life and
rarely presents before the age of 20 years. There is a slight female predominance.
Giant cell tumors are epiphyseal lesions that extend to the articular surface.
The distal femur and proximal tibia are the most common locations of giant cell
tumors followed by the distal radius and proximal humerus. These are painful
lesions that may be accompanied by a mass or swelling, or may be associated
with limitation of motion of the joint adjacent to the tumor and, on rare occasion,
a pathologic fracture. The primary radiographic features of giant cell tumors
relate to their eccentric, well delineated epiphyseal location with metaphyseal
extension, and the lack of reaction by the host bone. It is the lack of a sclerotic
margin and the presence of soft tissue infiltration that can give giant cell
tumors a rapidly destructive appearance and lead to mistaking them for malignant
processes. The tissue has a hemorrhagic, gray-brown appearance and may have
liquefied cystic and necrotic areas. The surrounding cortical bone is thinned
and there may be extension of the tumor into the adjacent soft tissues. The
lesion may extend to the articular cartilage which is rarely perforated. Under
the light microscope the tissue is composed of numerous multinucleated giant
cells that are uniformly distributed and separated by spindle and oval shaped
mononuclear cells. Both types of cells have a rather uniform appearance and
mitotic figures are present in the mononuclear cells. The histologic appearance
of the tumor may be altered when regressive or "healing changes" take
place or when a pathologic fracture has occurred. The tumor typically lacks
matrix production, but not infrequently, reactive new bone formation may be
found. The majority of giant cell tumors are benign and the degree of local
recurrence following curettage is not related to the histologic grading of the
tumor (grade 1 or 2). Therefore, the grading has no practical value. Rarely,
these lesions can metastasize to the lungs. Malignant giant cell tumor (grade
3) without previous radiation is extremely rare. Giant cell tumor should be
differentiated from other benign lesions with giant cells, such as nonossifying
fibroma, aneurysmal bone cyst, giant cell reparative granuloma, and Brown tumor
of hyperparathyroidism. The age of the patient, laboratory data, tumor location,
and radiograph, as well as the histologic appearances of the lesions are important
distinguishing features.
The treatment and prognosis of the tumor depends upon its clinical and radiographic
presentation. Patients with radiographic stage 1 and 2 lesions (Enneking) may
be treated with curettage and bone grafting or methylmethacrylate packing. Stage
3 lesions which show marked cortical destruction and prominent soft tissue infiltration
are best suited to en bloc resection. Cryosurgery and chemical ablation have
been utilized as adjuvants to local resection. Unresectable tumors may be treated
with radiation; however concerns regarding the potential for malignant degeneration
of irradiated giant cell tumors limits the efficacy of this treatment option.
Aggressive local soft tissue and joint involvement may necessitate either amputation
or extensive joint reconstruction. Recurrence rate following curettage only
has been reported in the past to be as high as 40 percent. Recently, thorough
curettage with cement packing has decreased recurrence to less than 25 percent.
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