The diagnosis of cancer entails an attempt to accurately
identify the anatomical site of origin of the malignancy and
the type of cells involved. Cancer can arise in any organ
or tissue in the body except fingernails, hair, and teeth.
The site refers to the location of the cancer within the
body. The body part in which cancer first develops is known
as the primary site. A cancer's primary site may determine
how the tumor will behave; whether and where it may spread
(metastasize) and what symptoms it is most likely to cause.
The most common sites in which cancer develops include the
skin, lungs, female breasts, prostate, colon and rectum, and
corpus uteri.
Secondary site refers to the body part where metastasized
cancer cells grow and form secondary tumors. A cancer is always
described in terms of the primary site, even if it has spread
to another part of the body. For instance, advanced breast
cancer that has spread to the lymph nodes under the arm and
to the bone and lungs is always considered breast cancer (and
the spread to the lymph nodes, bones, and lungs describe the
stage of the cancer).
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As is the case with other medical conditions,
there are many signs and symptoms that may indicate
the presence of cancer. These may be observed directly,
through imaging technologies, or confirmed by lab tests.
However, these signs and symptoms of cancer may resemble
those of other conditions. For example, weight loss
and abdominal pain can be caused by stomach cancer or
an ulcer. Pink or reddish urine can
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be caused by kidney cancer or a kidney infection. A positive
fecal occult blood test can indicate a variety of intestinal
problems. A biopsy (removal of tissue for microscopic evaluation)
is preferred to establish, or rule out, a diagnosis of cancer.
Tissue samples can be easily retrieved from a tumor near
the body's surface. If the mass is inaccessible, an imaging
exam that enables a tumor to be located precisely and visualized
may be ordered before the biopsy is performed.
The histological type is determined
by microscopic examination of suspected tissue that
has been excised by biopsy or surgical resection. If
the histological type is different from what is usually
found in the tissue being examined, it can mean the
cancer has spread to that area from some primary site.
Metastasis can occur by direct extension, via the blood
stream or the lymphatic system, or by seeding or implantation
of cancer cells.
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A biopsy, together with advanced imaging technologies, may
not only confirm the presence of cancer, but may also pinpoint
the primary site and secondary site(s).
It is also important to identify the cell type(s). Various
histological types have different growth rates and dissimilar
prognoses. More than one histological type of cell may be
found in the same site. For example, a tumor whose primary
site is skin can be a basal cell carcinoma, a squamous cell
carcinoma, or a melanoma.
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Once cancer has been confirmed, the
pathologist tries to determine how closely the cancer
cells resemble healthy, mature cells. Such cells are
said to be differentiated. Cancer cells that do not
look like their healthy counterparts are called undifferentiated,
or, because they often look like very immature cells,
primitive. The pathologist assigns a pathological grade
to a tumor according to how aggressive the tissue looks
under the microscope. Tumor grades can be expressed
in words or
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by a number. One set of terms consists of well differentiated
(grade 1), moderately differentiated (grade 2), poorly differentiated
(grade 3), or undifferentiated (grade 4). When tumors are graded
by number (1 through 4), a grade-1 tumor has a better natural
history than a grade-4 tumor does.
Cancers are further classified according to stage. Staging
describes how far a cancer has progressed based on the size
of the primary tumor and whether and/or where it has spread.
Go to Summary Staging and Summary Stage 2000 training module
by clicking here
for more details on cancer staging.
In summary, a biopsy is the preferred method to confirm the
diagnosis of cancer. Biopsies can provide information about
histological type, classification, grade, potential aggressiveness
and other information that may help determine the best treatment.
More information regarding cancer treatment is provided in
the
Cancer Treatment training module.
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