Scientific and medical terms related to cancer

 

As you research more about cancer and treatment options on the internet, you may discover unfamiliar terms. Here we will try to explain some of the common terms to help you understand them. If you find more unfamiliar terms than you can find here, please let us know and we will make the appropriate information available here.

Angiogenesis:
Forming a new vessel is called angiogenesis.

• Angiogenesis is a necessary process for normal tissues and organs.
• However, when a cancer grows it also grows new vessels to supply itself blood and nutrients.
• The vessels grow inside a cancer is different than normal vessels grow in a normal tissue or organ.

 

Anti-angiogenesis is to block new vessels from forming inside cancers and to change the forms and shapes of vessels inside cancer to make cancer more susceptible to chemotherapy.

• A new generation of drugs aiming at anti-angiogenesis has been developed and has had good clinical application for treating cancer as well as other diseases (such as macular degeneration for diabetic patients).

 

Cancer and tumor:
Cancer is a consequence of a normal cell gone out of control and becomes a malignant cell that grows to too many cells and spreads beyond where it starts.

• We also call it malignant tumor.
• Tumor can mean benign tumor or malignant tumor (cancer).
• Benign tumor does not normally spread beyond where it starts, while cancer can spread (this is called metastasis).
• Cancer can be fatal, while most benign tumors are not fatal.

 

Benign tumor can evolve and become a cancer.

• One example is breast cancer.
• One term commonly met by breast cancer patients is ductal carcinoma in situ (DCIS).
• This is benign tumor and does not spread.
• DCIS is also called pre-cancerous tumor.
• However, it can evolve to become cancer overtime if not treated.

 

Cancer-causing viruses:
Some viruses can cause cancer, most don’t.

• Viruses that can cause cancer including HPV (human papilloma virus), EBV (Epstein-Barr virus), hepatitis B and C, and others.
• HPV causes cervical cancer and head and neck cancer by inactivating the p53 protein.

 

Cell cycle:
The process of a cell going through a cycle of cell division is for the purpose of producing the next generation of cells.

• For example, everyday, more than one billion blood cells die and new ones are being made.
• Our skin changes cells every minute and that is partly why we have to take shower all the time.

 

Cancer stem cells:
Stem cells from normal tissue and organs are critical to renewal of our blood and regeneration of our tissues and organs.

• Everyday,  more than one billion blood cells die and are made.
• Everyday new skin cells are made.
• As a result, stem cell research is currently one of the hottest areas of scientific and medical research.

Cancer stem cell is a relatively new concept in cancer research.

• It is hypothesized that in a given cancer there is only a small population of cancer stem cells that can renew themselves and continue to supply new cancer cells, while most of the cancer cells do not have the capacity to renew and grow new cells more than a few generations.
• A group of researchers purified one single breast cancer cell from a breast cancer and grew it to a cancer on nude mice. This was one of the best evidences of cancer stem cell.
• However, there are scientists who do not believe that cancer stem cells exist and the debate is not resolved yet.

 

Cell signaling:
Hormones, growth factors, cytokines can not work by themselves.

• For hormones like estrogen, they go inside cells to deliver signals to their receptors and cause cells to do subsequent things.
• When a growth factor delivers signals, it finds its receptor on the surface of a cell.
• That receptor then sends signals through a cascade of proteins to deliver signals into the nucleus of the cell.
• One example is EGF receptor that is often mutated in non-small cell lung cancer.

 

Gene profiling:
Gene profiling is a technology developed in the recent year that can test tens of thousands of genes in one experiment or test.

• By using this technology scientists have been able to understand impact of a set of genes on a cancer or a treatment or can help predict prognosis and tailoring treatment.
• The most successful test developed for cancer using gene profiling is called OncotypeDx, a test for predicting the risk of relapse of breast cancer that is positive for estrogen and/or progesterone receptors.
• It can also help predict in certain patients if chemotherapy would be beneficial or not.
• This test combines 21 genes in one test and can give a score called Risk Score (RS) that tells approximately how high (or low) a patient’s risk of relapse is.
• This test is only helpful in patients whose tumor is positive for estrogen and/or progesterone receptors and whose breast cancer is in early stage.

 

Genes:
Genes are fragments of DNA that contain codes for making proteins for our cells.

• Each human cell contains approximately 30,000 genes. Each gene can have multiple functions and can have different function in different organs or tissues.

 

Gene testing:
Gene testing can be done in cancer cells or in normal white blood cells.

• When testing cancer cells for a gene, it is to find out if that the cancer harbors a specific mutated gene that can make that cancer resistant or susceptible to a therapy.
• For example, a gene called Kras can be mutated in more than one third of advanced colorectal cancers, which makes the cancer resistant to two drugs: cetuximab and panitumumab.

When testing normal white blood cells, the test is done for finding out if that person harbors a gene that can be inherited to the next generation.

• Sometimes, this kind of test can be done through taking a sample of oral buccal swab or saliva. 
• Not all patients with family history of cancer need to have gene testing.
• In fact only minority of patients may need to have the test done to make sure they do not carry a mutated gene that makes them and their family members susceptible to having cancer.

 

Immunotherapy:
Taking advantage of immune system to treat a disease (including cancer) is called immunotherapy.

• Immunotherapy includes using antibody against a protein to treat cancer, like rituximab for B-cell lymphoma, or using a vaccine, like a vaccine developed for prostate cancer that is refractory to hormonal therapy.
• Drugs such as interferon or interleukin-2 developed for kidney cancer or melanoma are also called immunotherapy.

 

Monoclonal antibody:
Human antibodies are made by a type of blood cell called plasma cell.

• Animals make antibodies too.
• Plasma cell can make unlimited number of different kind of antibody.
• Antibody is a critical part of immune system and is critical to protecting human body from foreign bugs (bacteria, viruses, fungus, ect…).

 

Monoclonal antibody is a kind of antibody that targets on one specific antigen (such as a specific protein).

• Discovery of monoclonal antibody in 1970’s revolutionized our understanding of immune system and made the targeted therapy a dream at that time for treating human diseases.
• Monoclonal antibody was called Golden bullet at that time, but it took another twenty years before a real drug was developed that truly made a golden bullet treating human disease possible.
• This drug is called rituximab or rituxan.

 

Monoclonal antibody is made through a very elegant process by selecting one clone of cell that makes just one kind of antibody that targets on one antigen.

• This clone of cell can make unlimited amount of the desired monoclonal antibody if you keep them grow and replicate.

 

Metastasis:
The process a cancer that spreads beyond where it starts is called metastasis.

• Only malignant tumor (cancer) can metastasize.
• Most of the cancers have a relatively unique pattern of metastasis.
• For example, prostate cancer often metastasize to bones first, colon cancer spreads to liver before it cancer spread to lungs, rectal cancer can spread to lungs before it spreads to liver.

 

Microscopic disease:
Cancer that can be identified by CT scans, MRI, PET scan or other imaging studies is called measurable disease.

Cancer that is too small to be detected by all these means is called microscopic disease.

• For example, a patient with early stage breast cancer has the gross cancer removed, but her oncologist may still recommend chemotherapy. Why? Because that some patients can still harbor microscopic cancer cells (microscopic disease) somewhere in body and chemotherapy may be able to kill them and get the patient cured.
• One-centimeter volume of a cancer contains approximately one billion cancer cells.

 

Mutations:
Changes of DNA codes of the genes are called mutations.

• A tiny change of just one DNA code in a gene can make that gene completely out of control and do many things harmful to a normal cell and cause a normal cell to become bad.
• It takes at least mutations of several genes for a cell to become a cancer.
• But one mutation can kick off a process that can lead to subsequent mutations of other genes of the cell that contain the mutation does not die (called programmed cell death).
• In some situations, cancer can start in a large area of a tissue or organ.
• This is called field cancerization. This can happen in head and neck cancer where the whole respiratory tract may be exposed to smoking.

Mutations that occur only in cancer cells are called somatic mutations.

• A gene mutation that causes hereditary cancers in patients with familiar cancer syndrome is called germ-line mutation and exists in all cells of that patient.
• For example, a patient who carries BRCA1 and develops breast cancer not only has the mutated gene in the cancer cells but also in all cells of all tissues and organs.

 

Oncogene:
An Oncogene is a gene that can cause cancer when it goes out of control.

• In normal human cells there are many genes called proto-oncogene.
• These genes are essential for our body function, but when they get to mutated they become oncogenes.
• For example a gene called KRAS, is mutated in more than 30-50% of advanced colorectal cancers and cause resistance of the cancer to become resistant to some drugs.

 

Programmed cell death:
Programmed cell death is a normal process that is programmed in every animal cell including cells of a tiny little worm called C. elegans.

 

During development, some cells need to die in order for a tissue or organ to form properly. For example, animal digits are not separated into digits until a certain stage in fetus. Some cells between the digits need to die in order for digits to form. This phenomenon was observed in chicks decades ago.

 

When a gene has gone bad (developing a mutation or other changes), or DNA got broken (for example, by sun’s UV light exposure, or other source of radiation), it could trigger the process of programmed cell death inside the cell and the cell would die. If this cell does not die the cell could continue to develop more mutations and become a cell that is more abnormal and eventually a totally bad cell. Another is when is cell is going through a process of self replicating (cell division), but a DNA breaks happens, the cell division process is supposed to stop. If it does not stop, the cell can get out of control and develop mutations and replicate wrong codes.

 

Many genes are important in maintaining a normal programmed cell death process in cells, these include p53, death receptors, caspases, ect.

 

Many genes do the opposite by preventing cell death, called anti-apoptosis. These genes include BCL-2, inhibitor of apoptosis protein (c-IAP) genes, cyclin D, ect…

 

One important mechanism for chemotherapy and radiation to kill cancer is by triggering programmed cell death in cancer cells.

 

 

Targeted therapy:
A drug that targets on a specific gene or protein is called targeted therapeutic, and using this targeted therapeutic for treating cancer is called targeted therapy.

 

The first targeted therapy developed for treating cancer was a drug called rituxan (rituximab), for treating B-cell lymphoma, developed by Professor Ronald Levy at Stanford University. This drug is an monoclonal antibody and targets a protein on the surface of B-cells called CD20. This drug has saved tens of thousands of life. The drug is usually well tolerated but can still cause some side effects such as allergic reaction. Because B cells are important for immune system, patients with hepatitis B or C may flare because of receving this drug and requires careful monitoring and treatment.

 

Another example of targeted therapy is imatinib (gleevec), developed for treating a type of leukemia called CML (chronic myelogenous leukemia) and has revolutionized cancer therapy. It targets three genes.

 

Erlotinib (tarceva) is another example that targets a protein called EGF receptor (epidermal growth factor receptor) and can be used for treating non-small cell lung cancer. It is especially effective for patients whose tumor carries a mutation of EGF receptor. This mutation occurs more frequently in patients who never smoked.

 

Targeted therapy targets on a specific gene or protein and can be effective on one or more than one particular cancer. However, it does not mean these drugs cannot cause side effects in organs or tissues. Sometimes some side effects could be quite challenging or serious.

 

For example, erlotinib can cause skin rash in 85% of patients taking it. It can also cause fatigue, diarrhea, swelling and liver function abnormalities.

 

 

Tumor suppressor gene:

A gene that can suppress cancer from growing is called tumor suppressor gene. Tumor suppressor genes are extremely important in our human cells to maintain normal cell growth as well as other functions. When a tumor becomes mutated inside a cell, the cell can grow abnormally and become a cancer cell. For example, BRCA1 is a tumor suppressor gene and is mutated in all cells of patients with hereditary breast/ovarian cancer syndrome. Another tumor suppressor gene called p53 is mutated in approximately 50% of all cancers.