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
LY M P Hor BLOODcirculation. A metastasized cancer
retains the characteristics of the tumor of origin.
For example, PROSTATE CANCERthat metastasizes to
the BONEis 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 treat-
ment is a RECURRENCE. Metastasis may be evident
at the time of diagnosis or may occur after treat-
ment.
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 pro-
mote growth or regulate APOPTOSIS (natural cell
death). The drugs that target them may be signal-
transduction 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 wide-

spread 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 molecu-

larly 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 abnor-

mally 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 nor-

mal controls. MOLECULARLY TARGETED THERAPIESand

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 pro-

teins, and how much of them, to produce to direct

the cell’s own growth. These proteins, called sig-

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