The National Cancer Institute defines histopathology as "the examination of diseased cells and tissues under a microscope." Histology is the study of tissues and pathology is the study of disease. Thus, histopathology literally means the study of tissue in relation to disease.
The histopathology report describes the tissue sent for examination and what the cancer looks like under the microscope . The histopathology report is sometimes called a biopsy report or pathology report.
A medical specialist who examines under a microscope is called a pathologist . The tissue to be examined comes from a biopsy or surgical procedure in which a sample of suspicious tissue is taken and sent to a laboratory.
It is then processed and cut into very thin layers (called slices), stained, and examined under a microscope to characterize the details of the cells in the tissue.
For some conditions, the surgeon can interpret a tissue sample very quickly using frozen sections. However, frozen sections or sections are rarely used for lymphoma due to interpretation and sampling issues .
In lymphomas, the lymph nodes are the tissue most frequently examined in histopathology. For many types of blood cancers, a bone marrow biopsy may also be required to make a definitive diagnosis.
Components of a histopathology report
Histopathological reports of surgical cancer specimens are increasingly complex. They may include:
- Microscopic view of affected tissue
- Special places
- Molecular methods
- Other tests
Molecular techniques refer to the ability to analyze cells and tissues at the molecular level, that is, at the level of proteins, receptors, and genes that encode these things.
Interpretation of the histopathology report
Many of the results of this tissue exam are related to prognosis. Predictive indicators can include the extent of the tumor and the extent of its spread, and whether the cancer has been removed with few healthy cells around it, or whether there is evidence that the cancer has spread beyond what was removed.
Scoring systems differ depending on the type of cancer being tested, but cells are generally scored based on how abnormal they look under the microscope; Grade 1 tumors appear more normal and grade 4 tumors reflect more abnormalities .
Therefore, a high-grade tumor is usually a tumor with more abnormalities in its cells. Evaluation is not the same as staging. The stage has more to do with where the cancer is in the body and how far it has spread.
In addition to histopathology, other methods, including fine needle aspiration cytology, can be used to assess the presence of cancer in tissues, and some of these methods can be used more widely in healthcare settings around the world.
Leukemias and lymphomas are diagnosed by a combination of their appearance:
- Cytochemistry: enzymes that can trigger certain chemical reactions.
- Immunophenotype: markers or surface proteins that can be detected by antibody tests.
- Karyotype: chromosomal changes
- Morphology: what cells look like
Other sampling methods
Immunohistochemistry involves the use of antibodies to bind to specific tags or markers on the outside of cancer cells. These markers, to which antibodies bind, are often referred to as "CD", which stands for group of differentiation.
For example, CD23 and CD5 are microscopic markers that, if present on cancer cells, can support the idea that chronic lymphocytic leukemia (CLL) / small lymphocytic lymphoma (SLL) is a possible diagnosis.
However, these same markers are also present in other cancers, so doctors use a kind of elimination process based on the information available and what is known about various cancers and their "typical" CD markers.
Another example of a CD marker is CD20, which is present in some lymphomas but absent in others. Diffuse large B-cell lymphoma, or DLBCL, is a very common lymphoma associated with the CD20 marker.
For a given sample of leukemia or lymphoma cells, markers can be tested using a full panel of antibodies that adhere to various markers, with positive and negative controls included.
Molecular and chromosomal studies can be done to look at genetic rearrangements and specific chromosomal changes. Sometimes inserted or deleted genes are associated with prognostic information.
For example, in chronic lymphocytic leukemia or CLL, a specific piece of the chromosome is lost, and a gene that helps suppress cancer is often lost along with it .
In general, a 17p deletion is found in approximately 5-10% of people with CLL. CLL with a 17p deletion is a form of CLL that is more difficult to treat with conventional chemotherapy .