Cancer antigens are proteins produced by cancer cells that can trigger an immune response. There are different types of antigens including tumor-specific antigens only expressed by cancer cells, overexpressed antigens, and those that are expressed in normal and cancer cells. Cancer antigen tests performed on blood, urine, or tissues can serve as biomarkers to detect certain cancers or monitor treatment effectiveness. Positive tests indicate a higher likelihood of cancer but do not definitively diagnose cancer. Antigens can also be targeted by antibodies to help detect and treat cancer.

2. Cancer : class of diseases characterized by out-
.of-control cell growth in the body
There are over 100 different types of cancer, and
each is classified by the type of cell that is
,initially affected
.Cancerous cells are also called malignant cells
Antigen: An antigen is any substance that causes
the immune system to produce antibodies
.against it
An antigen may be a foreign substance from the
environment such as chemicals, bacteria, or
.viruses
An antigen may also be formed within the body,
as with bacterial toxins or tissue cells

3. .Antigenic substance produced in cancer cells
Normal proteins in the body are not antigenic
thus any protein that is not exposed to the
immune system triggers an immune response
Exp‘ of -proteins that are normally produced in
extremely small quantities, or proteins that
are normally produced only in certain stages
.of development
The body‘s own immune system is able to
specifically distinguish between normal and
cancer cells by recognizing cancer antigens
displayed on the tumor cell‘s surface

4. Classification of cancer antigens is based
on their molecular structure and source.
Among the cancer antigens-
some may be tumor specific (PSA-prostate
specific antigen )
while others may also be expressed by
normal tissues “cancer associated
antigen”
(Cancer antigen 125-is the most important
cancer associated).

5. Differentiation antigen - a molecule expressed by one
particular tissue-type, and also by cancer cells derived
.from that tissue-type
For example, the tyrosinase and Melan-A/MART-1 antigens:
are expressed in normal skin melanocyte cells, and in most
.melanomas, but not other cell types in the body
Mutation and splice variant antigens - alterations in the DNA
sequence of a gene frequently result in differences in the
gene‘s protein sequence when the mutation alters one or
more amino acids in the protein. An alteration in the
messenger RNA (mRNA) sequence, may cause the mRNA
to be spliced differently, producing different forms of the
.protein
For example, the NY-CO-38 antigen has four splice variants,
.each of which has a different tissue expression

6. Over expressed /antigen - a protein that is over expressed in
a cancer cell compared to a normal cell. For example
normal epidermal growth factor receptor (EGFR) can be
distinguished by a specific targeted antibody when over
.expressed
CT antigens - proteins expressed only in normal ’germ line‘
tissues (testis, placenta, and embryonic and fetal ovary)
and in cancer cells. Because germ line cells do not express
major histo-compatibility complex (MHC) molecules, the
cells are unable to present antigens on their surface, thus
.a cancer therapy would not target these normal cells
The NY-ESO-1 antigen: it is expressed in testis, in a variety of
tumors such as melanoma, breast, ovary, prostate,
.bladder, sarcoma, and lung
Viral antigens– viral proteins are expressed in infected human
cells and these viral proteins, or the peptide fragments
resulting from the processing of the proteins, are presented
.to, and recognized by, the immune system

7. Cancer markers:
most are found in low levels in healthy persons
used to stage cancer, to indicate a prognosis, to monitor treatment,
or in follow-up to watch for cancer recurrence.
Some cancer markers are associated with many types of cancer.
Once cancer is diagnosed, cancer marker levels sometimes help to
determine the extent of cancer. Higher levels can indicate more
advanced cancer and a worse prognosis in some cases.
The patient and their physician may use this information to choose
between more or less aggressive treatments.
Depending upon the cancer marker, it can be measured in blood,
urine, stool or tissue. Some widely used cancer markers include:
AFP, CA 15-3, CA 19-9, CA 125, CEA..
Alphafetoprotein(AFP):Germ cell tumors& hepato cellular
carcinoma.
Carcinoembryonic antigen: (CEA)bowel cancers, Occasional lung
or breast cancer.
CA-125:Ovarian cancer.
MUC-1:breast cancer.
epithelial tumor antigen:(ETA)breast cancer.
Tyrosinase : malignant melanoma, normally present in minute
quantities greatly elevated levels in melanoma.

8. Melanoma-associated antigen
(MAGE)malignant melanoma ,also
.normally present in the testis
CA19-9- as a screening test for cancer,
.particularly pancreatic cancer
Ca 72-4-gastric cancer
PSA-prostate specific antigen is a protein
produced by cells of the prostate gland in
.man

9. Cancer Antigen Tests
Cancer antigen tests are tests for proteins,
carbohydrates, and hormones that serve
as markers for cancer. These markers
can be found in different fluids and
tissues of the body. Antigen tests are
done with blood, urine, occasionally with
other body fluids, and tissue samples.
When a cancer antigen test comes
back positive, the antigen was found.
Although a positive result does not mean
that the cancer is present, it does mean
that there is a greater chance of having
that cancer1

10. Gastrointestinal Cancer Antigen Tests
Tumor M2-PK
Colo-rectal, stomach, pancreas, esophagus, breast,
cervical, and skin
CA 19-9
Pancreas (most common), liver, colon, non-malignant
CEA
Colorectal (predominant in combination with CA195)
along with markers for stomach, pancreas, lung,
breast, and medullary thyroid
CA 72-4
Stomach
Exist also gender ,lung, bone categories of cancers*
. antigens

11. An antibody ,known as an immunoglobulin, is
a large Y-shaped protein produced by B-
cells that is used by the immune system to
identify and neutralize foreign objects such
as bacteria and viruses. The antibody
recognizes a unique part of the foreign
target, called an antigen.
In most cases, interaction of the B cell with a
T-helper cell is necessary to produce full
activation of the B cell and, therefore,
antibody generation following antigen
binding.

12. .Antigens triggers an immune response in the host
Tumor antigens are useful in identifying tumor cells and
.are potential candidates for use in cancer therapy
The role of these antigens is to attract antibody targets
for diagnostic and therapeutic applications, because
it hes antibodies may enable early detection of the
tumor, in many cases antibody binding to tumor cells
leads to destruction of these cells through a process
known as antigen-dependent cellular cytotoxicity
the antibody can be conjugated to a "payload" such
as a toxin which is targeted to the cancer cell by the
antibody and thus kills the cancer cell but spares
.normal cells

13. http://www.panomics.com/index.php?id=produc
/http://www.ncbi.nlm.nih.gov/books/NBK13896
http://www.antibody.com/index2.html
http://clincancerres.aacrjournals.org/content
/15/17/5323.full
http://medical-
dictionary.thefreedictionary.com/Tumor+m
arkers