How can a primary tumor be distinguished from a secondary tumor? I tried finding it on the internet but it only said that they are found by means of immunohistology but I couldn't understand how.Please elaborate
The difference is pretty easy to understand. The secondary tumors is metastiesed tumor sped to enother parts of body. On the other hand the primary tumor is the source of the metastiesed.
I give you one example of this. On of the most common tumor of testicles is seminoma metastiesed to the peritonium, lungs, brain.
The secondary tumor is usually hard to distinguised with primary. But usually if there is specific antigen which can be recognised by antibody. The antibody is usually cultivated in mice. But this antibody have to be recognised by enother antibody. The second antibody to mice antibody is cultivated usually in rats. After that the secondary antibody is usually modified by fluorescent chemical. This is indirect immunohistochemistry. Direct is usually only the first antibody modifided by some fluorescent.
So first of all you have to do biopsy of that potential tumor. After that the sample is usually fixated by freazing and sliced by cryomicrotom. Than samples is usually put in to petry dish and poor with izotonic solution. Then the primary antibody is add. It take some time to react (find the antigen), thereafter is add the secondary antibody. To view the antibody you have to activated fluorescent by laser in fluorescent microscope. So if the fluorescent is in the sample, the tumor should be secondary.
Nevertheless is still hard to distinguish secondary tumor from the primery. Usually is up to experiencies with the tumors and how they are behave in body of patient. This is one of the reasons why is hard to treat the cancer.
Different tissues express different proteins, and cancers are often allocated to their primary tissue by virtue of expressing proteins specific to the type of tissue they arose in. Of course, with primary tumours there is also the advantage of imaging ; lung cancer, for example, can be localised to the lung based on a PET scan.
Sometimes though there are cancers of unknown primary , where a metastasis is picked up, but allocation to the primary tumour is not possible because it wasn't detected. In this case, it is possible to use epigenetic profiles to predict the tissue of origin for the tumours in question. See https://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(16)30297-2/fulltext