most bone cancers. COMPUTED TOMOGRAPHY (CT)
SCAN, MAGNETIC RESONANCE IMAGING (MRI), and
radioisotope bone scan can provide greater detail
about the tumor to aid in its diagnosis. POSITRON
EMISSION TOMOGRAPHY(PET) SCANcan detect whether
or to what extent the cancer has metastasized to
other sites in the body. A blood test to measure the
level of alkaline phosphatase, an enzyme
osteoblasts release when configuring new bone tis-
sue, may suggest—though cannot confirm—bone
cancer. Blood levels of this enzyme are normally
high during periods of bone growth. Biopsy of the
tumor provides the definitive diagnosis.
Treatment Options and Outlook
Treatment depends on the location and size of the
tumor. Treatment options for primary bone can-
cers include CHEMOTHERAPY, radiation therapy, and
surgery to remove the tumor. Often, radiation
therapy or chemotherapy administered first can
shrink the tumor so the surgeon can remove it
without the need to amputate the involved limb.
Oncologists often administer chemotherapy both
before and after surgery. The course of
chemotherapy before surgery is typically 8 to 10
weeks; chemotherapy after surgery may extend
for a year. The oncologist is likely to add radiation
therapy to the treatment regimen when there are
metastases the surgeon cannot safely remove.
Treatment for metastatic cancer of the bone
depends on the type of primary cancer and the
degree of METASTASIS.
The outlook after treatment depends on the
extent of cancer present at the time of diagnosis.
Significant surgery, such as AMPUTATION, requires
intensive rehabilitation. The outlook for metastatic
cancer of the bone depends on the type of primary
cancer and the aggressiveness of metastatic disease.
Risk Factors and Preventive MeasuresThough Ewing’s sarcoma has a clear genetic con-
nection, doctors know little about the risk factors
for and causes of other forms of primary bone
cancer. Radiation exposure, such as radiation ther-
apy to treat a different cancer, increases the risk
for osteosarcoma. There are no measures known
to prevent bone cancer.
See also BREAST CANCER; CANCER TREATMENT
OPTIONS AND DECISIONS; COLORECTAL CANCER; PAGET’S
DISEASE OF THE BONE; PROSTATE CANCER; SURGERY FOR
CANCER.bone density The amount of mineral, primarily
calcium, the bones contain that gives them their
mass. BONEdensity is important to give the SKELE-
TONenough structure to support the body. Insuffi-
cient bone density results in the bone loss
conditions OSTEOPENIAand OSTEOPOROSIS. Numerous
hormones participate in maintaining bone density.
Among them are estrogen, TESTOSTERONE, CALCI-
TONIN, vitamin D (in the form of calciferol), and
PARATHYROID HORMONE. Though calcium is the min-
eral most commonly associated with bone struc-
ture and bone density, other minerals that also are
important, including magnesium and phosphorus.
Bone density naturally diminishes with increas-
ing age, beginning at about age 35, at a rate of
about 2 percent per year. Because estrogen is par-
ticularly essential for maintaining bone density in
women, bone density drops precipitously at
MENOPAUSEwhen a woman’s estrogen production
drops to nearly nothing. Because men’s bodies are
larger, they inherently have greater bone mass.
Testosterone contributes to this mass, as it does a
man’s greater MUSCLEmass. The natural decrease
in bone density is usually not a health concern
until a man reaches his middle to late 60s.Disorders of Bone Density
Most health problems related to bone density arise
from diminished bone mass, which presents
increased risk for bone FRACTURE. Spontaneous
fracture (fracture that occurs without trauma or
other cause) is possible when bone density is very
low. The spine and the hip are at particular risk.
The most common of these conditions are
osteopenia (bone loss that places the individual at
increased risk for fracture) and osteoporosis (bone
loss that places the individual at significant risk for
fracture). Compression fractures of the spine, in
which the vertebrae collapse, can endanger the
SPINAL CORD; HIP FRACTURE IN OLDER ADULTSis a key
cause of disability and death. Medications are
available that stimulate bone growth, helping
restore lost bone mass. The doctor may prescribe
such medications, along with lifestyle measures
such as RESISTANCE EXERCISE, to increase bone den-
sity. Excessive bone mass is far less common310 The Musculoskeletal System