Breast cancer immunohistochemistry
Immunohistochemistry is the process of identifying and labeling individual proteins found in breast tumors. Sometimes abbreviated as IHC, immunohistochemistry allows a pathologist to localize and identify the antigens (proteins) in tissue cells by finding the antibodies which bind to them. The root ‘histo‘ means tissue, while ‘immuno‘ refers to the immune systems, specifically, to antibodies. Through the use of protein-based stains, certain, ‘markers‘ may appear within and around the abnormal cells of a breast tumor, giving clues as to the biological/microscopic events which are occuring in the tumor.
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Biomarkers can be found in the blood, the urine, or by staining tumor cells
There are different ways that doctor’s can gain immunohistochemical information about a breast tumor, as different markers will show up in the urine, blood, or by staining the breast tumor itself. Most breast tumor markers are either proteins, parts of proteins, or hormones. Some breast tumor markers are caused by the body’s response to breast cancer, but they are frequently caused by benign conditions as well. Additionally, there are some tumor markers that are unique for a particular kind of breast cancer, while others are more general.
Some immunohistochemical biomarkers are used in all breast cancer evaluations, others are used in specific cases
There are common breast cancer tumor marker tests that are virtually always utilized, but they are more specialized marker tests used in individual cases, and new tumor markers in limited use or still in the research phase. The discovery of new biomarkers that seem to have prognostic and predictive significance has already brought about changes in the way breast cancer is treated and managed. In many cases, specific molecular subgroups present in a breast cancer tumor may lead to specific therapeutic decisions. Some of the newer biomarkers have a high predictive value, not specifically about the behavior of the tumor, but on how the breast carcinoma will respond to endocrine breast cancer therapy.
Common breast cancer markers
The most common breast cancer tumor marker tests are for Estrogen and Progesterone Receptors (ER and PR), and for the Human Epidural Growh FActor 2 (HER2/neu), which are tumor staining tests, and also tests for Urokinase Plasminogen Activator (uPA), and Plasminogen Activator Inhibitor (PAI-1), which are either blood or urine tests.
UPA and PAI-1 blood/urine tests measure breast cancer aggressiveness
The uPA or PAI-1 tests are given as prognostic indicators which can give a sense as to how aggressive the breast cancer is. Low levels of uPA and PAI-1 tend to indicate that if the lymph nodes are clear, the risk of breast cancer recurrence is low, That helps the doctor’s decide whether or not adjuvant chemotherapy would be beneficial or not. High levels of PAI-1 or uPA tends to predict a high likelihood of recurrence, and a decision might be made to use chemotherapy.
All breast cancers are different, but three biomarkers are used in every diagnosis
Breast cancers are of course not uniform, but has many different subtypes, with specific variables associated with each tumor. The specific molecular profile and biological behavior of every breast cancer needs to be determined as accurately as possible in order to plan and manage treatment, and immunohistochemical analysis is an essential component of this process. Presently, only three immunohistochemical markers, specifically estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2) levels are measured routinely in every breast cancer.
Without a doubt, the most important immunohistochemical marker used in breast cancer therapy is for the Estrogen receptor. The levels of estrogen receptor expression in a breast tumor is a very useful indicator in predicting breast cancer response to endocrine therapy. Approximately 80% of all breast cancers are ER-positive.
The level of progesterone receptors in a breast cancer tumor is also routinely evaluated. Typically, since the expression of progesterone is highly dependent on estrogen receptor levels to begin with, it is very uncommon to find a PR positive tumor which is ER negative. (only 1% of all breast cancers are PR+ ER-). Breast cancer tumors with high levels of ER but low levels of PR are more common, and it is generally believed that the response to endocrine therapy in metastatic breast cancers is better where both are in evidence.
HER2 is an oncogene which has been identified as a valid indicator of breast cancer prognosis. Over-expression of HER2 tends to lead to a higher rate of breast cancer relapse and shorter overall survival. HER2 amplification and over expression is found in about 15% of all breast cancers. If identified, women with HER2 breast tumors benefit significantly from anti-HER2 treatments. As such, HER2 should be assessed in virtually each new case of breast cancer.
Over expression vs. amplification
When a certain hormone receptor or gene is ‘over expressed‘, this means the the effect or product of a particular unit is excessive, more than it should be. This is subtly different from the concept of ‘amplification‘, which means that there are many more copies of a given unit of genetic material than there should be, and as a result, there is much more of its product in the breast tumor or blood.
Ki67 has in recent years emerged as an important immunohistochemical marker. Ki67 was found to be universally expressed among proliferating cancer cells, but absent in normal cells. As such, Ki67 has emerged as a marker for breast cancer proliferation. Baseline levels of Ki67 in a breast cancer tumor may be useful in predicting tumor response to chemotherapy. In fact, some breast cancers are now treated with pre-surgery chemotherapy (neoadjuvant therapy), and it is quite common to measure post-neoadjuvant chemotherapy levels of ki67 as a strong predictor for both overall survival and recurrence-free breast cancer survival. However, ki67 levels as a prognostic indicator does not yield consistent results among all studies, and so is not used in any standardized practice the way ER and PR levels are.
Cyclin D over expression has emerged as a useful prognostic indicator in breast cancers which are ER positive. It would appear, unfortunately, that high levels of Cyclin D in ER positive breast cancer patients tends to be a likely indicator of poor responsiveness to endocrine therapy. In many cases, high levels of cyclin D in a breast tumor leads to an early relapse.
Cyclin E has been associated with a primary role in breast cancer tumor genesis. There are inconsistent conclusions at present regarding the interpretation of Cyclin E levels as a prognostic indicator for breast cancer treatment. Some studies do cite higher Cyclin E levels with lower disease-free and overall breast cancer survival rates, but other studies conclude that Cyclin E levels do not have a statistically significant effect on breast cancer outcome.
ERbeta was only discovered in the mid 1990s, and is commonly expressed in the cells of several of the body’s organs. Higher levels of ERbeta proteins have been associated with a better response to tamoxifen, overall good prognosis, and a prolonged period of disease-free survival for breast cancer.
The p27 gene has recently been identified as a key regulator of certain phases of progression in the breast cancer mutation process. p27 itself is usually not mutated in breast cancers, but the ability of p27 to function as it normally would is impaired by breast cancer. As a result, reduced levels of the p27 protein have been strongly associated with a high histopathologic grade of the breast tumor. This is largely due to the fact that lower p27 levels tend to prevent the tumor from becoming highly differentiated. Consequently, loss of p27 in a tumor generally indicates a poorer patient outcome, even when the lymph node status is negative.
Molecular/genetic profiling has lead to four ‘molecular subtypes’ of breast tumors
Gene expression profiling in breast cancer tumors has led to the identification of molecularity distinct neoplastic breast diseases, which seem to develop from different cell types. There appear to be four ‘basic‘ types of molecular classification in breast cancer. These are:
1) Luminal breast cancers, which are usually ER positive. Within this group there are two subgroups;
2) Luminal A, which are of a low grade histologically, and Luminal B, which are of a higher grade and with a poorer prognosis.
3) HER2-positive breast tumors, which have high levels of the ERBB2 gene, do not express hormone receptors, and which tend to have a poor prognosis.
4) Basal-like breast cancers, which tend to be ‘triple negative‘ (ER- PR- HER2-) and which express cytokeratins of the basal epithelial layer, and also tending to have a poor prognosis.
Blood and bone marrow immunohistochemical markers
In the near future, additional immunohistochemical markers may be widely used which can detect single disseminating and circulating breast cancer cells in the bone marrow or in the blood. Other biochemical markers which are able to identify circulating cell-free DNA and microRNA may also be widely utilized in breast cancer treatment.
Circulating tumor cells
There has been an effort in recent years to come up with new methods to detect immunohistochemical biomarkers with minimally invasive methods. (without taking a biopsy sample). It has been known for a long time that cancer patients have circulating tumor cells (CTC) in their blood, but it is only recently that advances in molecular identification have made it possible to identify them consistently. A high CTC sound in breast cancer patients would tend to indicate either the presence of metastasis or a high likelihood of metastasis, which would be considered a negative prognostic indicator. If CTC levels do not go down, chemotherapy would most likely be initiated.
Circulating cell-free DNA
Another emerging approach to using non-invasive immunohistochemical analysis in the treatment of breast cancer is in monitoring levels of circulating cell-free DNA (cfDNA). DNA, mRNA, and microRNA are usually released by breast tumors and circulate in the blood. Changes in the levels of these circulating nucleic acids can be used as an indicator of ‘tumor burden‘ and progression to a malignant state. Ongoing measurement of cfDNA levels helps in assessing the prognosis and the effectiveness of breast cancer treatments.
Everything you need to know about immunohistochemistry is listed above.
For further reading, I suggest you visit this page on Detecting DCIS Microcalcifications.
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