How Exactly Does Chemotherapy Work?

It tends to be used to treat cancers that have metastasized (spread) to other parts of the body from the original source (aka primary tumor). 

The main goals of chemotherapy are to:- 

• Kill cancer completely (best result),
• Control the spread and growth of cancer, and;
• Palliation, or easing the severity of pain of a particular disease like cancer.  

The dose, schedule, and drugs used for chemotherapy will depend on the type of cancer in question, the patient's medical history, body surface area and weight, age, and the stage that any discovered cancer is at. Treatment frequencies tend to vary, but can be consecutive days followed by periods of non-treatment to allow healthy body cells time to recover. 

How chemotherapy cures cancer

In the best cases, chemotherapy can cure cancer completely. In this sense, it means that cancer cells are completely destroyed, and prevented it from returning. 

Most doctors never actually use this term when it comes to cancer, though they may mention it as a possible outcome of the therapy. Like any drug-related treatment, there is never a guarantee of a cure, although that is ultimately the goal. 

That being said it does happen but it tends to take many years and may not remove all cancer cells from the body.

How chemotherapy is used to control cancer

Where a complete cure is not possible, chemotherapy is often used to at least control cancer's growth and spread. Chemo can, and often does, shrink tumors and contains the cancer to its existing locations.

In most cases, chemo doesn't completely destroy all traces of cancer but is effective at managing chronic cases. In this sense, it can be likened to heart disease or diabetes treatments. 

In some other cases, cancer may have been successfully treated initially but is later shown to return. If this occurs, chemotherapy can be re-administered again. 

How chemo is used to palliate cancer

The last main use for chemotherapy in cancer victims is for palliation. Usually called palliative chemotherapy, or simply palliation, it is used to ease the symptoms caused by cancer.

This is usually administered in the late, or advanced, stages of cancer and cannot control or prevent the spread of an already chronic case. In these circumstances, chemo can be used to shrink one or more tumors that are causing the patient extreme pain or pressure. 

How does a chemo treatment work?

You may, or may not, already know that the drugs used in chemotherapy for treating cancer work by targeting fast-growing or dividing cells. This includes many of the patient's normal cells like those found in the skin, hair, intestines and bone marrow. 

Once administered, the cocktail of drugs circulate throughout the patient's body in the bloodstream. For this reason, it is also known as a form of systemic treatment.

The drugs are specially designed to target and kill cells in the process of dividing or splitting in two. Human bodies are made up of billions of cells and, when fully grown, most cells in the human body don't divide and multiply that often. 

They tend to only need to do this when they need to repair some damage. When they do divide, it tends to be relatively controlled and predictable. 

"When cells divide, they split into 2 identical new cells. So where there was 1 cell, there are now 2. Then these divide to make 4, then 8 and so on." - Cancer Research UK. 

Cancer cells, on the other hand, keep on dividing until there is a mass of cells. These masses of cells tend to be called lumps or tumors. 

Because cancer cells are constantly dividing they are most likely to be affected by the drugs used for chemo. But, unfortunately, there tends to be some collateral damage to normal dividing cells at the same time.

This is mostly unavoidable as chemotherapy treatment targets the entire body rather than a specific site like surgery or radiation therapy. Sadly this is a major side-effect or drawback of chemo over other treatment methods. 

Administered chemo drugs do this by either damaging the cell's genes in its nucleus or disrupting the cell during division. 

"Some drugs damage cells at the point of splitting. Some damage the cells while they're making copies of all their genes before they split. Chemotherapy is much less likely to damage cells that are at rest, such as most normal cells.

You might have a combination of different chemotherapy drugs. This will include drugs that damage cells at different stages in the process of cell division. This means there's more chance of killing more cells." - Cancer Research UK. 

What is the success rate of chemotherapy?

The chances of success of chemotherapy vary depending on the type of cancer in question. It tends to work very well for cancers like testicular cancer and Hodgkin lymphoma, for example.

However, for other cancers, chemo will never cure it on its own. In these cases, chemo tends to form part of a package of other treatments. 

For cancers like breast cancer or bowel cancer, surgery is the primary treatment followed by a course of chemo to help prevent remission (return). For difficult-to-cure cancers, chemo may also be used to help shrink tumors, relieve symptoms and generall extend/improve the quality of life of a patient. 

In one 2006 study, a team did manage to quantify the success of chemo for lung patient sufferers. By collecting and studying 761 tumor samples, they found a particular protein called ERCC1 which had long been suspected of allowing certain cancers to be chemo-resistant. 

According to their results, tumors that lacked the protein often saw improved efficacy of chemo with most living at least 14 months longer with 47% still alive after five years. ERCC1 carrying tumors, however, showed no marked improvement from chemo. 

In fact, patients who didn't receive chemo tended to live a little longer than those who did. But for other cancers, the results are pretty encouraging. According to the American Cancer Society's 2016-2017 report, cancer survival rates from chemo are pretty good. 

Percentages vary from anywhere as low as a few percent up to 90%+ depending on the cancer type and its stage of development. 

Can chemotherapy kill you?

Given how chemotherapy works, there is a chance that the therapy can kill the patient. "Kill or cure" as the old adage goes. 

A British inquiry into the use of chemotherapy back in 2008, found that it was just over a quarter of patients.

"The [National Confidential Enquiry into Patient Outcome and Death] NCEPOD inquiry investigated more than 600 deaths within 30 days of receiving chemotherapy either as a cancer treatment or as palliative care to lessen the symptoms."

Results showed 43% of patients suffered significant treatment-related toxicity despite receiving other treatment to reduce the chemotherapy side effects.

Inquiry advisers believe more than one in four of the patients died from these side effects rather than from cancer – a concern when 14% of patients were taking the treatment to cure them of cancer.

In fact, the inquiry concluded that 19% of those who died should not have been receiving the treatment at all". - Pharma Times. 

Other inquiries in the UK in 2016 also found worryingly high numbers of patient deaths from chemo too. But as worrying as that sounds, the chances of survival from cancer without any treatment are relatively low meaning that the potential benefits of cure or control far outweigh the risks.