Identifying the type of cell from which a cancer has developed is a specialized art. The doctors who make these judgments are pathologists, and their job is absolutely critical! If the oncologist does not know what the type of cancer is, he or she does not know how to treat it. The pathology and diagnosis of GIST are recently beginning to be well understood. Given the critical job of the pathologist, newly diagnosed GIST patients may sometimes consider a second opinion of their pathology reports (unless the pathology was initially done by a pathologist who was very experienced with GIST). While many pathologists may be able to accurately diagnose GIST now, predicting the behavior of GIST can be difficult. Experience is important here. A team of doctors and pathologists who are all experienced with GIST will often be better able to develop and implement a specific treatment plan based on each patients unique situation.
A biopsy is usually used to aid in the diagnosis of cancer and GIST. Tissue samples are prepared from the biopsy sample. One method that the pathologist uses to classify tissues is called immunohistochemistry. Using this technique, the pathologist applies various “antibodies” to the tissues. These antibodies are each designed to react with specific features (proteins) on the cell surface. The most important antibody that is applied when GIST is suspected is the KIT antibody. When these antibodies bind to their specific target on the cell surface they produce a “stain” or change in color of the sample. So when the KIT antibody is applied, if the cell surface has the KIT protein present on the surface, the sample will “stain positive”. This is what is known as “KIT positive” and means that this cell has KIT receptors on its surface.
With rare exceptions, GIST tumors will stain positive for KIT. This means that the cell is manufacturing or using the KIT protein. In the case of KIT, this protein is a receptor. (See KIT Receptor Image)
- KIT positive-about 95% of the time (the term c-Kit or CD117 may be used instead of KIT).
- DOG-1 positive – about 98% of the time
- CD34 positive-60% to 70% of the time.
- SMA postive-30% to 40% of the time.
- Desmin positive-very rare
- S-100 positive-5%+
- PKC theta (PKCθ) is expressed in almost all GIST but that may not be commercially available.
- Increasingly, a negative stain for SDHB is helping to identify pediatric-type GIST.