What is Chemotherapy?
Chemotherapy involves the use of potent chemical agents to treat cancer by specifically targeting and destroying rapidly dividing cells. This treatment is fundamental in oncology and is often used alone or in conjunction with other modalities such as surgery and radiation therapy. The primary objectives of chemotherapy are to inhibit tumor growth, shrink existing tumors, and ultimately eliminate cancer cells from the body.
Chemotherapy drugs function by disrupting the cell cycle, particularly focusing on cells that are actively dividing. Cancer cells proliferate at a significantly faster rate than normal cells, making them more vulnerable to these treatments.
Types of Chemotherapy
| Chemotherapy Class | Chemotherapy Drugs | Mechanism of Action | Route of Administration (ROA) | Possible Side Effects | Application |
| Alkylating Agents | Chlorambucil | Directly damage DNA, preventing cell division. | Oral | Nausea, vomiting, decreased blood cell counts, reversible hair loss, bladder damage, fertility impairment | Chronic lymphocytic leukemia (CLL) and some lymphomas. |
| Cyclophosphamide | Add alkyl groups to DNA, causing cross-linking and strand breaks. | Oral, Intravenous (IV) | Nausea, vomiting, abdominal pain, decreased appetite, reversible hair loss, bladder damage, potential lung or heart damage (with high doses) | Breast cancer, lymphoma, and leukemia. | |
| Busulfan | Inhibit DNA replication and repair. | Oral, Intravenous (IV) | Nausea and vomiting, decreased blood cell counts, kidney damage, hearing loss, electrolyte imbalances | Chronic myelogenous leukemia (CML). | |
| Cisplatin | Form cross-links in DNA, leading to apoptosis. | Intravenous (IV) | Nausea and vomiting, decreased blood cell counts, kidney damage, hearing loss, electrolyte imbalances | Ovarian, bladder, and lung cancers. | |
| Antimetabolites | Methotrexate | Mimic natural substrates, disrupt DNA and RNA synthesis. | Oral, Intravenous (IV), Intramuscular (IM) | Nausea and vomiting, mouth ulcers, skin rashes, photosensitivity, dizziness, rare kidney and liver damage, reversible hair loss | Leukemia, lymphoma, breast cancer, and osteosarcoma. |
| Fluorouracil | Inhibit thymidylate synthase, affecting DNA synthesis. | Intravenous (IV), Oral | Nausea and vomiting, diarrhea, mouth ulcers, photosensitivity, dry skin | Colorectal cancer and other solid tumors. | |
| Gemcitabine | Incorporate into DNA, leading to chain termination during replication. | Intravenous (IV), Subcutaneous (SC) | Nausea and vomiting, fever and flu-like symptoms, rash, decreased blood cell counts | Pancreatic cancer, non-small cell lung cancer, and bladder cancer. | |
| Azacitidine | Azacitidine inhibits DNA methyltransferase, resulting in hypomethylation, and is incorporated into RNA and DNA, leading to cytotoxic effects. | Intravenous (IV), Subcutaneous (SC) | Nausea, vomiting, fatigue, diarrhea, constipation, fever, injection site reactions, myelosuppression, and an increased risk of infections. | Myelodysplastic syndromes and acute myeloid leukemia (AML). | |
| Antitumor Antibiotics | Doxorubicin | Intercalate into DNA, inhibiting RNA synthesis and disrupting replication. | Intravenous (IV) | Mouth ulcers, reversible hair loss, nausea and vomiting, risk of heart damage (cardiomyopathy) | Breast cancer, bladder cancer, and lymphoma. |
| Bleomycin | Induce DNA strand breaks through free radical formation. | Intravenous (IV), Intramuscular (IM) | Skin rash, pulmonary toxicity (pulmonary fibrosis), mouth sores | Hodgkin's lymphoma and testicular cancer. | |
| Mitoxantrone | Inhibit topoisomerase II, preventing DNA unwinding. | Intravenous (IV) | Nausea and vomiting, decreased blood cell counts, mouth sores | Prostate cancer and certain types of leukemia. | |
| Epirubicin | It stabilizes the topoisomerase II-DNA complex, leading to DNA strand breakage and generates free radicals that contribute to cellular damage. | Intravenous (IV) | Nausea, vomiting, fatigue, myelosuppression, cardiotoxicity, mouth sores, hair loss, and an increased risk of infections. | Breast cancer | |
| Plant Alkaloids | Vincristine | Prevent microtubule formation, blocking mitosis (M phase). | Intravenous (IV) | Numbness or tingling in fingers/toes (peripheral neuropathy), constipation, reversible hair loss | Leukemia, lymphomas, and pediatric cancers. |
| Paclitaxel | Stabilize microtubules, preventing their disassembly during cell division. | Intravenous (IV) | Allergic reactions, nausea and vomiting, reversible hair loss, numbness or tingling in fingers/toes | Breast, ovarian, lung cancers, and Kaposi's sarcoma. | |
| Etoposide | Inhibit topoisomerase II, leading to DNA damage during replication. | Intravenous (IV), Oral | Reversible hair loss, nausea and vomiting, decreased blood cell counts | Testicular cancer and small cell lung cancer. | |
| Nitrosoureas | Carmustine | Alkylate DNA and inhibit its repair mechanisms; can cross the blood-brain barrier. | Intravenous (IV), Intracavitary | Nausea and vomiting, decreased blood cell counts, lung toxicity | Brain tumors and multiple myeloma. |
| Lomustine | Similar action as alkylating agents, effective against brain tumors. | Oral | Nausea and vomiting, decreased blood cell counts | Brain tumors and Hodgkin's lymphoma. | |
| Streptozocin | Streptozocin alkylates DNA in pancreatic beta cells by utilizing the GLUT2 transporter, leading to cell death and the generation of reactive oxygen species (ROS). | Intravenous (IV) | Nausea, vomiting, kidney damage, hypoglycemia, liver toxicity, myelosuppression, allergic reactions, and hypertriglyceridemia. | Pancreatic islet cell tumors (insulinomas). | |
| Others | |||||
How Chemotherapy Works?
Chemotherapy is a treatment method that uses powerful chemical agents to combat cancer by specifically targeting and destroying rapidly dividing cells. It primarily works by damaging the DNA within these cells, which inhibits their ability to replicate. Cancer cells exhibit uncontrolled growth and division, often occurring at a significantly faster rate than normal cells, making them more susceptible to chemotherapy drugs designed to disrupt the cell cycle the series of phases that cells undergo as they grow and divide. By targeting the cell cycle, chemotherapy effectively hinders the growth of cancerous cells, preventing them from multiplying and ultimately leading to their death. This targeted approach is essential in cancer treatment, as it aims to reduce tumor size and eliminate cancerous growths from the body.
Basic Principles of Chemotherapy Explained by Phase and Duration
Chemotherapy is a treatment method that specifically targets cancer cells during distinct phases of the cell cycle. Understanding these phases and their durations is crucial for maximizing the effectiveness of chemotherapy. Below is an overview of the cell cycle phases, their durations, and the corresponding principles of chemotherapy.
Cell Cycle Phases and Their Durations
| Cell Cycle Phase | Duration (hours) | Chemotherapy Principle |
| Gap 0 (G0) | Variable (resting phase) | Cells are not actively dividing; chemotherapy is less effective during this phase. |
| Gap 1 (G1) | Variable | Cells grow and prepare for DNA synthesis; some drugs can target cells in this phase. |
| DNA synthesis (S Phase) | 6 – 12 | DNA synthesis occurs; this phase is highly sensitive to chemotherapeutic agents that damage DNA.Z |
| Gap 2 (G2) | 2 – 10 | Cells prepare for mitosis; certain drugs can interfere with preparations for division. |
| Mitosis (M) | 0.5 – 1 | Active cell division occurs; drugs such as vinca alkaloids and taxanes target this phase to prevent mitosis. |
Role of Chemotherapy in Cancer Treatment
Chemotherapy is an essential component of cancer treatment, tailored to meet the specific needs of individual patients. Below is a concise overview of its primary roles:
| Role | Description |
| Curative Chemotherapy | Aims to completely eradicate cancer from the body, typically used when cancer is localized and manageable. Certain cancers, such as testicular cancer and some leukemias, respond well to treatment. The objective is to achieve no detectable cancer cells. |
| Palliative Chemotherapy | Focuses on alleviating symptoms without curing the disease, particularly relevant when cancer has metastasized or is inoperable. Aims to enhance comfort by managing pain and other distressing symptoms. It helps shrink tumors causing discomfort, improving overall well-being for patients in advanced stages. |
| Adjuvant Chemotherapy | Given after primary treatments like surgery to eliminate remaining cancer cells and reduce recurrence risk. Target microscopic disease not removed during surgery. Commonly used in breast, colorectal, and lung cancers to improve survival rates. |
| Neoadjuvant Chemotherapy | Administered before primary treatments to shrink tumors for easier surgical removal or enhanced radiation effectiveness. Reduces size before surgery. This approach can improve surgical outcomes and may allow for less extensive surgeries. |
Conclusion
Chemotherapy drugs are essential in cancer treatment, specifically designed to target and eliminate rapidly dividing cancer cells. Each class of these drugs operates through distinct mechanisms that disrupt crucial processes necessary for cancer cell growth. However, while they effectively target cancer cells, they can also impact normal, healthy cells, leading to common side effects such as nausea, hair loss, and increased susceptibility to infections.
The choice of chemotherapy regimen is influenced by factors such as the type and stage of cancer and the patient's overall health, necessitating personalized treatment plans for optimal effectiveness. As research progresses, new chemotherapy agents and combinations are being developed to improve efficacy while minimizing adverse effects. This ongoing innovation is vital for enhancing patient outcomes and providing hope to those affected by cancer. In summary, chemotherapy remains a fundamental tool in oncology, continually evolving through research to deliver more effective treatments and improve the quality of life for patients battling cancer.
