Encyclopedia of Health and Medicine

M–O
metastasis Cancer that spreads beyond its site of
its origin. Metastasis may be local (extend outside
the original tumor but remain near the original
site), regional (remain in the general vicinity of
the original site), or distant (in organs or tissues
elsewhere in the body from the original site). It
may occur as a result of direct invasion of adjacent
tissues and organs or when cancer cells enter the
LYMPH or BLOOD circulation. A metastasized cancer
retains the characteristics of the tumor of origin.
For example, PROSTATE CANCER that metastasizes to
the BONE is metastatic prostate cancer, not BONE
CANCER. The type of cancer is an important factor
in determining the most effective treatment. The
LUNGS, LIVER, and bone are the most common sites
for metastasis. Cancer that comes back after treatment
is a RECURRENCE. Metastasis may be evident
at the time of diagnosis or may occur after treatment.
See also CANCER TREATMENT OPTIONS AND DECI-
SIONS; REMISSION.
molecularly targeted therapies Treatment
approaches for cancer that interfere with specific
molecular functions within cancer cells to prevent
them from dividing. The most significant benefit
of molecularly targeted therapies is that they can
selectively alter the function of specific cancer
cells without affecting the function of normal
cells. They do so primarily by targeting the protein
signals cancer cells use that regulate their growth
and division. These signals may be ones that promote
growth or regulate APOPTOSIS (natural cell
death). The drugs that target them may be signaltransduction
inhibitors (also called small-molecule
drugs), apoptosis-inducing drugs, and MONOCLONAL
ANTIBODIES (MABS).
Current molecularly targeted therapies are
especially promising for cancers that have a widespread
presence in a vital organ or throughout the
body, such as small-cell LUNG CANCER (SCLC) and
MULTIPLE MYELOMA, which makes them difficult to
treat through other approaches. Because molecularly
targeted therapies are so new, doctors do not
know their risks or long-term consequences or the
extent to which they may be effective in treating
cancers in general.
DRUGS USED IN MOLECULARLY TARGETED THERAPIES
bortezomib (Velcade)
gefitinib (Iressa)
imatinib mesylate (Gleevec) oblimersen (Genasense)
rituximab (Rituxan)
trastuzumab (Herceptin)
See also CANCER TREATMENT OPTIONS AND DECI-
SIONS; CELL STRUCTURE AND FUNCTION; CHEMOTHERAPY;
IMMUNOTHERAPY; ONCOGENES; TUMOR SUPPRESSOR
GENES.
oncogenes Mutated proto-oncognes that abnormally
infuence the rate of growth of cells.
Researchers believe oncogenes play a role in the
development of cancer by altering cellular growth
through one or more mechanisms. Oncogenes
may accelerate cell division, block APOPTOSIS
(planned cell death), or in other ways allow cells
to grow beyond the boundaries of the body’s normal
controls. MOLECULARLY TARGETED THERAPIES and
MONOCLONAL ANTIBODIES (MABS) show significant
promise for altering oncogenes to reduce their role
in the development of cancer.
Proto-oncogenes are the normal genes which
contain the genetic code that tells cells which proteins,
and how much of them, to produce to direct
the cell’s own growth. These proteins, called sig-
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