Cancer : class of diseases characterized by out-.of-control cell growth in the bodyThere are over 100 different types of cancer, andeach is classified by the type of cell that is,initially affected.Cancerous cells are also called malignant cellsAntigen: An antigen is any substance that causesthe immune system to produce antibodies .against itAn antigen may be a foreign substance from theenvironment such as chemicals, bacteria, or.virusesAn antigen may also be formed within the body, as with bacterial toxins or tissue cells
.Antigenic substance produced in cancer cellsNormal proteins in the body are not antigenicthus any protein that is not exposed to the immune system triggers an immune responseExp‘ of -proteins that are normally produced inextremely small quantities, or proteins thatare normally produced only in certain stages.of developmentThe body‘s own immune system is able to specifically distinguish between normal andcancer cells by recognizing cancer antigensdisplayed on the tumor cell‘s surface
Classification of cancer antigens is basedon 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).
Differentiation antigen - a molecule expressed by oneparticular tissue-type, and also by cancer cells derived.from that tissue-typeFor 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 bodyMutation and splice variant antigens - alterations in the DNAsequence of a gene frequently result in differences in thegene‘s protein sequence when the mutation alters one ormore amino acids in the protein. An alteration in themessenger RNA (mRNA) sequence, may cause the mRNAto be spliced differently, producing different forms of the.proteinFor example, the NY-CO-38 antigen has four splice variants,.each of which has a different tissue expression
Over expressed /antigen - a protein that is over expressed ina cancer cell compared to a normal cell. For examplenormal epidermal growth factor receptor (EGFR) can bedistinguished by a specific targeted antibody when over.expressedCT 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 expressmajor histo-compatibility complex (MHC) molecules, thecells are unable to present antigens on their surface, thus .a cancer therapy would not target these normal cellsThe NY-ESO-1 antigen: it is expressed in testis, in a variety oftumors such as melanoma, breast, ovary, prostate,.bladder, sarcoma, and lungViral antigens– viral proteins are expressed in infected humancells and these viral proteins, or the peptide fragmentsresulting from the processing of the proteins, are presented.to, and recognized by, the immune system
Cancer markers:most are found in low levels in healthy personsused 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.
Melanoma-associated antigen(MAGE)malignant melanoma ,also.normally present in the testisCA19-9- as a screening test for cancer,.particularly pancreatic cancerCa 72-4-gastric cancerPSA-prostate specific antigen is a proteinproduced by cells of the prostate gland in.man
Cancer Antigen TestsCancer antigen tests are tests for proteins,carbohydrates, and hormones that serveas markers for cancer. These markerscan be found in different fluids andtissues of the body. Antigen tests aredone with blood, urine, occasionally withother body fluids, and tissue samples.When a cancer antigen test comesback positive, the antigen was found.Although a positive result does not meanthat the cancer is present, it does meanthat there is a greater chance of havingthat cancer1
Gastrointestinal Cancer Antigen Tests Tumor M2-PKColo-rectal, stomach, pancreas, esophagus, breast,cervical, and skin CA 19-9Pancreas (most common), liver, colon, non-malignant CEAColorectal (predominant in combination with CA195)along with markers for stomach, pancreas, lung, breast, and medullary thyroidCA 72-4StomachExist also gender ,lung, bone categories of cancers*. antigens
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.
.Antigens triggers an immune response in the hostTumor antigens are useful in identifying tumor cells and.are potential candidates for use in cancer therapyThe role of these antigens is to attract antibody targetsfor diagnostic and therapeutic applications, becauseit hes antibodies may enable early detection of thetumor, in many cases antibody binding to tumor cellsleads to destruction of these cells through a process known as antigen-dependent cellular cytotoxicitythe antibody can be conjugated to a "payload" suchas a toxin which is targeted to the cancer cell by theantibody and thus kills the cancer cell but spares.normal cells