How Chemotherapy Drugs Impact Cells, Patients, and the Healthcare System

What Is Cancer?

According to the CDC Cancer Data and Statistics, there were 1,752,735 new cancer diagnoses and nearly 600,000 deaths in 2019 alone.

The National Cancer Institute (NCI) states, “cancer is a disease in which some of the body’s cells grow uncontrollably and spread to other parts of the body.” This uncontrolled cell proliferation can lead to damaged cells or tissue lumps called tumors.

“Cancerous tumors spread into or invade nearby tissues and can travel to distant places in the body to form new tumors (a process called metastasis). Cancerous tumors may also be called malignant tumors. Many cancers form solid tumors, but cancers of the blood, such as leukemias, generally do not.”

Cancer cells do not require signals to grow like normal cells. Additionally, they ignore signs to cease division or die.

Types of Chemotherapy Drugs

Because there are multiple kinds of chemotherapy drugs, these drugs can be combined into various treatment regimens depending on the patient, cancer type, and progression. Certain drugs fit into multiple categories and can be used in numerous ways.

Alkylating Agents

Alkylating agents are one kind of chemotherapy drug that prevents cell proliferation by damaging DNA.

The NCI SEER Training Module describes alkylating agents as the most common chemotherapy drug. The type of DNA damage varies based on the exact alkylating agent. Alkylating agents may cause the following:

• DNA cross-linking
• abnormal base pairing
• DNA strand breakage

These agents can impact cells at any point of the cell cycle. While these are effective for many kinds of cancer, they may not work well for very aggressive cancer growths.

Despite the potential benefits of alkylating agents, providers must be cautious when including this kind of chemotherapy. High doses of alkylating agents can damage the bone marrow and lead to leukemia; as treatment time is prolonged, the risk of leukemia from alkylating agents increases. ACS states that the risk of leukemia is the highest between 5 and 10 years after treatment.

Most alkylating agents cannot pass through the blood–brain barrier (BBB) and, therefore, cannot treat cancers that affect the brain. However, nitrosoureas are a class of alkylating agents that can cross the BBB.

Antimetabolites

Antimetabolites are an additional class of chemotherapy drugs that substitute the standard building blocks of RNA and DNA, thus interfering with cell division. The NCI SEER Training Module notes that antimetabolites “mimic nutrients that the cell needs to grow, tricking the cell into consuming them, so it eventually starves to death.”

These chemotherapy drugs primarily target the S-phase of the cell cycle, where DNA is synthesized.

Anti-Tumor Antibiotics

Another class of chemotherapy drugs is anti-tumor antibiotics. The ACS suggests, “These drugs are unlike the antibiotics used to treat infections. They work by changing the DNA inside cancer cells to keep them from growing and multiplying.”

One type of anti-tumor antibiotic is anthracycline, which inhibits the enzymes required for DNA replication by binding directly to DNA.

While these drugs have proven beneficial in eliminating or slowing cancer progression, they are associated with an increased risk of permanent heart damage. The lifetime dose limits are used with this category of medications to reduce the overall adverse outcomes.

Plant Alkaloids

The NCI states, “Plant alkaloids are antitumor agents derived from plants. These drugs act specifically by blocking the ability of a cancer cell to divide and become two cells. Although they act throughout the cell cycle, some are more effective during the S- and M-phases, making these drugs cell-cycle specific.”

Topoisomerase inhibitors — sometimes referred to as plant alkaloids — prevent topoisomerase from separating the strands of DNA for DNA replication. There are two topoisomerase inhibitors: topoisomerase I inhibitors and topoisomerase II inhibitors.

Mitotic inhibitors — also known as plant alkaloids — prevent cell division by arresting the cell in the mitotic phase. Despite the name, mitotic inhibitors can damage proteins needed for cell division at any cell cycle phase.

Mitotic inhibitors include taxanes and vinca alkaloids.

Corticosteroids

ACS defines corticosteroids as “natural hormones and hormone-like drugs that are useful in the treatment of many types of cancer, as well as other illnesses. When these drugs are used as part of cancer treatment, they are considered chemotherapy drugs.” 

In addition to these categories, there are also other chemotherapy drugs that do not fit well into one of these categories.

Impacts of Chemotherapy

According to the American Society of Clinical Oncology (ASCO), the side effects of chemotherapy are heavily variably and impacted by the type of cancer, drug and dose, comorbidities, and more.

Physical Impacts

The major impacts of chemotherapy drugs are interrupting the cell cycle and killing the cells. Cancer cells will proliferate more rapidly than healthy cells. Despite the goal of chemotherapy to prevent cancerous cells from multiplying, chemotherapy cannot differentiate between cancerous and healthy cells.

While most people find this worrisome, the ACS states, “the good news is that most normal cells will recover from the effects of chemo over time. But cancer cells are mutated (not normal) cells, and they usually do not recover from the effects of chemo. This is why chemo is good at killing many types of cancer cells.”

Side effects of chemotherapy include fatigue, nausea, diarrhea, mouth sores, hair loss, and anemia.

Neurological and Emotional Impacts

In addition to the physical side effects of chemotherapy, there are also emotional implications. The CDC highlights stress, anxiety, depression, loneliness, and anger as cancer treatment outcomes.

“Chemo brain” is a common term used to describe neurological deficits associated with chemo and cancer treatments. “Emotional and mental health challenges such as depression, anxiety, stress, and having trouble sleeping can add to that foggy feeling. Chemo brain can also intensify feelings of frustration or anger,” states the CDC.

There are treatments and coping mechanisms for the emotional side effects caused by cancer treatment. Therapists and mental health professionals are an essential part of the care team for oncology patients.

Financial Impacts

The cost of chemotherapy varies depending on the type of cancer, duration of treatment, stage of illness, type of chemotherapy, and multiple other factors.

According to research published by the NCI, in 2020, the total spending on cancer in the US was $208.9 billion. Of that cost, medical services contributed $188.1 billion and prescription drugs — including chemotherapy — amounted to $20.9 billion.

Prescription medications for female breast cancer have the highest cost at $3.5 billion, with leukemia coming in second at $3.2 billion. However, the lowest spending recorded was for uterine cancer, which did not fit into the billions range.

Implications

Understanding the kinds of chemotherapy and its cellular and physical impact can help inform healthcare decisions for patients and providers. Often chemotherapy is used in combination with other cancer treatments such as hormone therapy, surgical interventions, and radiation therapy.

Patients and families of those undergoing chemotherapy should be aware of and monitor chemotherapy's potential physical, neurological, and emotional side effects. Additionally, the public is urged to make lifestyle changes to reduce the risk of cancer, such as cessation of smoking, drug, and alcohol use, healthy eating habits, regular physical activity, and regular checkups with a licensed healthcare professional.