An Introduction to the Biological Basis of Cancer
I love teaching and education. If you know of my history of teaching experiences, it’s easy to see this. There is a dearth of introductory, well cited pieces, on scientific topics for people who have a basic knowledge of science and want to learn more. Here I present an introductory piece on the biology of cancer with a molecular basis. This article assumes basic knowledge of biology.
What is cancer?
Cancer is a general term for a broad range of diseases where cell growth is unchecked due to breakage in regulatory mechanisms.   This is why diagnosis for some cancers is as simple as feeling for lumps; uncontrolled growth leads to masses in tissues.
Why does this occur?
Cancer occurs due to mutations in DNA. These mutations can occur due to a number of factors which include chemicals, viruses, radiation, and heredity.  Using the central dogma of biology, we can then conclude that mutations in DNA will eventually lead to creation of proteins which are not normally found in the cell. These mutations will either augment or diminish protein functions within a cell, leading to an abnormal cell. While there are safeguards within the cell to discover and repair these errors in the DNA, when those mechanisms are mutated, these abnormal cells then duplicate and propagate via mitosis.  This will then lead to an accumulation of mutations in DNA.
Upon accumulation of these mutations, cancer cells adopt new functions which, among many things, allow them to endlessly divide. Most cancer treatments target this narrow margin of functional difference that cancer cells acquire.  Chemotherapy is a general class of drugs which interfere with cell division, preventing not only cancer cells, but also normal cells from dividing. This is why patients undergoing chemotherapy lose their hair; cells within the hair follicle stop dividing and creating hair cells. Chemotherapy is askin to carpet bombing, the specificity of the drug is very low, and affects all cells in the body. The hope is that chemotherapy will affect cancer cells more so than normal cells and treat the disease. Unfortunately, cancer cells can also acquire new mutations which create functions to become resistant to drugs. 
Chronic myelogenous leukemia (CML), a Case Study
One of the greatest success stories in cancer research is the discovery and successful treatment of CML, a cancer of white blood cells. As mentioned earlier, cancer is a where mutations create or diminish cellular function. CML is a mutation where a transaction of chromosomes 9 and 22 occur, forming a new protein called the BCR-ABL fusion protein. That is, a piece of chromosome 9 and 22 get swapped in one’s genome. This swap then creates a new protein which inhibits DNA repair and promotes cell growth.  However, as explained earlier, cancer treatments are created to target differences between cancer and normal cells. Gleevec was created to target this BCR-ABL protein and inhibit its abnormal function, killing the cell. Since this protein was a product of abnormal chromosomal rearrangement, the BCR-ABL protein is not seen in regular cells. Before the discovery of Gleevec, only 30% of patients diagnosed with CML survived for five years after being diagnosed.  An independent study in 2011 found that after 6 years of treatment with imatinib (generic name for Gleevec), 94.9% of patients remained in remission.
The State of Cancer Research
Currently, the largest funding of cancer research comes from the NCI which has a budget of $4.9 billion per year. Due to the complexity of cancer, there are various potential targets where cancer drugs can target. For example, Gleevec is a form of targeted therapy where the protein product is targeted. However, again referring to the central dogma of biology, there are also gene therapy treatments which act at the DNA level and miRNA drugs which treat at the RNA level. While there will probably never be a single drug to cure cancer due to the fact that cancer is an entire class of diseases, individual advances which target different areas can be used in combinational therapy.
This post was inspired by Professor Clodagh O’Shea after she gave an excellent guest lecture for a genetics class. Her lab works on a novel form of cancer treatment where they engineer viruses to target and destroy cancer cells. This post is also dedicated to my mom.