Chemotherapy for oncology: general principles

Chemotherapy (CT) is a systemic treatment with anticancer drugs that aims to destroy or suppress the growth of cancer cells throughout the body, including micrometastases that are not visible on imaging studies. Unlike surgery and radiation therapy, which act locally, CT circulates through the bloodstream and reaches "hidden" lesions. Therefore, it is prescribed not only for advanced cancer but also after radical surgery to reduce the risk of disease recurrence. [1]

The goals of chemotherapy vary: neoadjuvant – before surgery or radiation, to shrink the tumor and increase the chances of organ preservation; adjuvant – after radical treatment, to "finish off" the remaining cells; palliative – in metastatic disease, to control symptoms and prolong life. The specific goal determines how "aggressive" the regimen will be and how many cycles will be planned. [2]

It's important to understand that today, chemotherapy is often combined with targeted and immunotherapy, or postponed if the tumor has vulnerable molecular targets. For example, for lung cancer with driver mutations, targeted drugs are started first, with chemotherapy added later or in combination with immunotherapy; for hormone-positive breast cancer, endocrine therapy and targeted drugs may be the first lines of treatment. However, in many conditions, chemotherapy remains the mainstay of treatment. [3]

The foundation of successful chemotherapy is supportive care: from antiemetic prophylaxis to hematopoiesis protection and effective pain management. These measures significantly improve the tolerability of treatments, facilitate adherence to the schedule, and, consequently, enhance the effectiveness of the entire plan. [4]

When chemotherapy is indicated: principles of administration

Doctors prescribe chemotherapy when the expected absolute benefit outweighs the risks of toxicity. In early-stage disease with a high risk of recurrence, adjuvant courses have been proven to improve survival (for example, stage III colon cancer). In locally advanced disease, neoadjuvant therapy helps "shrink" the tumor to make it operable or improve radiation therapy. In metastatic disease, chemotherapy is chosen if it can quickly reduce symptomatic lesions and buy time for other interventions. [5]

The decision is influenced by the biology of the tumor. Some subtypes (for example, gastrointestinal stromal tumors) are almost ineffective in responding to classical chemotherapy; targeted therapy is the preferred treatment option. Others, such as synovial sarcoma or small cell lung cancer, are, on the contrary, sensitive to cytostatics and often demonstrate a rapid clinical response. Correct routing and diagnostic verification are critical. [6]

Systemic therapy is inevitably planned by a team (surgeon, clinical oncologist, radiation oncologist, pathologist, radiologist): this facilitates the selection of the order of actions—surgery → adjuvant or neoadjuvant → surgery → adjuvant—and the timely initiation of radiation or targeted/immune options. This standard is reflected in the relevant ESMO guidelines. [7]

If the expected benefit is moderate and the risk of toxicity is high (due to age, comorbidities), de-escalation is discussed—more lenient regimens, shorter durations, or a transition to observation after local treatment. The decision is made jointly with the patient, discussing the expected benefit and possible side effects. [8]

How to choose a scheme: factors that matter

The choice of chemotherapy regimen depends on the tumor type and subtype, stage, treatment goals, as well as your overall health and comorbidities. Doctors consider molecular markers (for example, MSI/MMR in colorectal cancer), as they can alter the order: in some patients, immunotherapy can outperform chemotherapy in terms of effectiveness. However, if there are no molecular targets or no response is expected, they start with the "classical" approach. [9]

When discussing the regimen, the team always considers emetogenicity (the potential for vomiting)—this determines antiemetic prophylaxis. For highly emetogenic combinations, triple or even quadruple antiemetic regimens (5-HT3 antagonist, NK1 antagonist, dexamethasone ± olanzapine) are prescribed on the day of infusion. This allows most patients to complete the course without uncontrollable nausea. [10]

The risk of febrile neutropenia (a dangerous infection caused by a drop in white blood cell count) is also assessed. If the risk is high (usually ≥20% based on the regimen and patient factors), prophylaxis with leukocyte growth factors (G-CSF) is prescribed to avoid cycle interruptions and hospitalizations. This standard is supported by the ASCO/ESMO consensus and real-world practice. [11]

Finally, transfusion thresholds for anemia are planned in advance: current AABB guidelines support a "restrictive" strategy—considering transfusions, as a rule, at hemoglobin levels below 70 g/L in stable adults, individualizing the decision based on symptoms and comorbidities. This approach reduces risks without worsening outcomes. [12]

How the courses are conducted: cycles, accesses, forms of introduction

Chemotherapy is administered in cycles: infusion or oral administration → recovery window → next cycle. Typical intervals are 14, 21, or 28 days, depending on the regimen. The number of cycles is determined by the goal: in adjuvant treatment, 3-6 cycles are most common; in metastatic disease, until maximum benefit is achieved or unacceptable toxicity is observed, with regular reassessment. [13]

Drugs are administered through peripheral veins or through long-term venous access (port/catheter) if frequent infusions or "harsh" drugs are planned. This makes treatment more convenient and safer for the veins. Oral regimens (capecitabine, etc.) are available for some tumors; these require the same discipline as infusions and regular monitoring. [14]

Before the start of each cycle, blood tests and patient's well-being are assessed. If severe neutropenia, anemia, or thrombocytopenia occurs, the cycle may be postponed, the dose may be reduced, or G-CSF/transfusion support may be added. This is a normal part of the process, not a "treatment failure": the goal is to complete effective therapy without dangerous complications. [15]

During treatment courses, response monitoring (CT/MRI according to RECIST or clinical laboratory criteria) is performed every 2-3 months to ensure the regimen is effective and toxicity is acceptable. If there is no effect, the plan is revised—changing the "partners," incorporating radiation/local therapies, or proposing a clinical trial. [16]

Side effects: what to expect and how to prevent them

Nausea and vomiting are no longer a "must-pay" option. With modern antiemetic protocols, they can be controlled in most patients, including late nausea on days 2-4. If prophylaxis fails, the regimen is strengthened (for example, by adding olanzapine). Always report symptoms to your team—this will help fine-tune the defenses. [17]

The most dangerous complication is febrile neutropenia: a temperature ≥38.0°C for ≥1 hour, or a single ≥38.3°C in a patient undergoing chemotherapy, requires immediate medical attention (this is not a "wait until morning" situation, but an emergency). Antibiotics are started within the first few hours, while the source of the infection is being investigated. The peak risk often occurs on days 7-12 of the cycle. [18]

Anemia and fatigue are common treatment complications. In cases of symptoms (shortness of breath, weakness) and low hemoglobin, transfusions are considered based on restrictive thresholds; in some situations, erythropoiesis stimulating agents are considered after iron deficiency has been ruled out. This strategy reduces the burden on the body and decreases hospitalizations. [19]

The skin, mucous membranes, and nervous system may also react: mucositis (inflammation of the mucous membranes) requires careful oral hygiene and prescribed rinses; peripheral neuropathy (numbness, tingling) requires dosage adjustments and the use of pain control agents. All these effects are manageable with early notification to the team. [20]

Modern combinations: when used together with immune and targeted therapy

For a number of tumors, combination therapies offer greater benefits than any single-mode strategy. In lung cancer without driver mutations, the addition of immunotherapy to platinum-based double-drug therapies improves survival; in HER2-positive breast cancer, chemotherapy is combined with anti-HER2 therapy; in colorectal cancer, targeted therapies are selected based on RAS/BRAF and the site of the primary tumor. This is the "new normal" of systemic treatment. [21]

At the same time, niche options after chemotherapy are expanding. For example, targeted molecules (pazopanib, trabectedin, eribulin) are used after chemotherapy for certain sarcomas, and TCR cell therapy afamitresgene autoleucel (TECELRA) has been available for synovial sarcoma in the US since 2024 in highly selected patients (HLA-A*02 and MAGE-A4 expression). This demonstrates how rapidly the landscape is changing. Chemotherapy remains a "platform" upon which new technologies are being deployed. [22]

Sometimes, on the contrary, targets are used first, and chemotherapy becomes a "reserve" (examples include driver mutations in non-small cell lung cancer and the KIT/PDGFRA mutation in GIST). What's important isn't the "ideology" of the method, but the sequence that provides the greatest benefit for you. [23]

With any combination, supportive measures (antiemetic protection, neutropenia prophylaxis) remain mandatory: they are equally important with both mono-chemotherapy and combination therapy. Precise prophylaxis regimens are published and regularly updated by MASCC/ESMO, ASCO, and NCCN. [24]

Home Safety: What to Do and When to Call the Doctor

Take your temperature at any chills, aches, or deterioration in your health. A call is required if your temperature is 38.0°C or higher (or a single 38.3°C). Avoid taking antipyretics "to get through the night"—they can mask the infection associated with neutropenia. Contact your doctor first. [25]

Practice good hand hygiene, be careful with raw foods, and wear a mask in crowded areas during virus season. These are simple but effective measures while your white blood cells are low. If you've been prescribed G-CSF for prophylaxis, stick to the injection schedule and don't change it without approval. [26]

Maintain fluid balance and nutrition: eat small, frequent meals; if nausea occurs, consume cold foods and drinks; avoid irritating foods. If vomiting or diarrhea prevents fluid retention, this is a reason for an unscheduled visit – dehydration is dangerous and can disrupt the course. [27]

Discuss an emergency plan with your team in advance: where to go, what to bring, and what medications are safe and unsafe to take before the examination. This reduces anxiety and saves valuable time if symptoms appear at night or on the weekend. [28]

Frequently asked questions

Is it possible to work or study while undergoing chemotherapy?
Often, yes, especially with good antiemetic protection and a flexible schedule. Plan rest periods for the first 2-4 days after infusions and inform your employer of any adjustments. [29]

Is chemotherapy dangerous for others?
Most regimens do not require isolation. Follow basic hygiene rules at home; your clinic will provide personalized recommendations (such as caution with body fluids for the first 48 hours). [30]

If I don't tolerate a regimen well, does that mean it's "potent" and effective?
Not necessarily. Effectiveness is assessed by tumor response, not by the severity of side effects. The goal is effectiveness and safety; doses and maintenance are adjusted as needed. [31]

What are the "red button" symptoms?
Temperature ≥38.0°C, uncontrollable vomiting/diarrhea, blood in the stool or urine, shortness of breath, severe weakness, confusion—call a doctor immediately. Better safe than sorry than to miss a dangerous complication. [32]