Clinical trials are one of the most important bridges between scientific discovery and real medical care. Before a new drug, procedure, diagnostic test, device, or therapeutic strategy becomes part of medical practice, it must be carefully studied to determine whether it is safe, whether it works, and which patients could benefit the most.

In cancer care, this process is especially important. Oncology is not a single field with one disease or one universal treatment. Cancer includes hundreds of biological conditions, each influenced by tumor type, genetics, immune behavior, stage, previous treatments, and patient-specific factors. That is why clinical trials are essential: they help medicine move from promising ideas to evidence-based decisions.

A clinical trial is a research study involving people. Its purpose is to evaluate a medical intervention under a defined protocol. That intervention may be a new drug, a combination of existing treatments, a surgical or image-guided procedure, a diagnostic method, a screening tool, a supportive care strategy, or a way to improve quality of life. The goal is not simply to “try something new,” but to answer a precise scientific and clinical question.

For patients and their families, clinical trials may seem complex at first. Terms such as phase I, randomization, placebo, blinding, eligibility criteria, outcomes, and informed consent may sound distant from everyday medical decisions. However, when these concepts are explained clearly, clinical trials become easier to understand: they are structured systems designed to protect participants while generating reliable medical knowledge.

 

Why clinical trials are necessary

A treatment may seem promising in the laboratory and still not work in humans. Cancer cells in a culture dish or tumors in animal models do not fully reproduce the complexity of a patient’s body. Human biology includes metabolism, immunity, organ function, genetic variability, previous treatments, comorbidities, and many other factors that can influence how a therapy behaves.

That is why clinical research is conducted in phases. Each phase answers a different question. Initial studies usually focus on safety and dosage. Later studies evaluate whether the treatment works better than existing options or whether it improves important outcomes such as tumor control, survival, symptom relief, or quality of life.

Clinical trials also help identify risks. A therapy may reduce tumor size but cause unacceptable toxicity. Another may be safe but not effective enough. Some treatments may work only in patients with specific biomarkers, mutations, immune profiles, or tumor characteristics. Without clinical trials, these differences would remain uncertain.

 

Figure 1. The drug discovery process moves from target identification and laboratory testing to human clinical trials, regulatory evaluation, and post-release monitoring.

 

Treatment trials

Treatment trials are one of the best-known types of clinical trials. They evaluate new therapies or new combinations of therapies. In oncology, this may include chemotherapy, immunotherapy, targeted therapy, radiation therapy strategies, ablation techniques, image-guided procedures, cellular therapies, vaccines, or combinations of standard treatments and investigational approaches.

A treatment trial may compare a new therapy with the current standard of care. It may also evaluate whether adding a new strategy to an existing treatment improves outcomes. In some cases, these trials focus on patients with limited options after standard therapies have stopped working. In other cases, they test whether a new approach can improve first-line treatment.

The key point is that treatment trials are not improvised care. They follow a protocol that defines who can participate, what treatment will be administered, how safety will be monitored, what outcomes will be measured, and when the results will be analyzed.

 

The phases of clinical trials

Clinical trials for new drugs or treatments usually progress through sequential phases. Each phase has a specific purpose.

Phase I trials are usually the first step of evaluation in humans. Their main goal is to assess safety, determine an appropriate dose, understand side effects, and study how the body processes the treatment. In oncology, phase I trials usually include patients with advanced cancer rather than healthy volunteers, because investigational cancer therapies may carry significant risks and are intended for serious disease contexts.

Phase II trials evaluate in greater detail whether the treatment shows signs of activity against a specific cancer or condition. These studies continue to monitor safety, but they begin to ask whether the therapy appears effective enough to justify larger trials. For example, a phase II oncology trial may evaluate tumor response, disease control, progression-free survival, biomarker changes, or immune activity.

Phase III trials are larger studies designed to confirm whether a treatment offers a significant benefit compared with standard therapy, placebo, or another control strategy. These trials usually provide much of the evidence used by regulatory agencies to decide whether a treatment should be approved. By including more participants, they can also detect less common side effects that may not have appeared in previous studies.

Phase IV trials are conducted after a treatment has been approved and is used more widely in clinical practice. These studies may monitor long-term safety, effectiveness in real-world populations, rare adverse events, or new uses of an already approved therapy.

Phases should not be understood as levels of “better” or “worse” treatment. They represent different stages of evidence. A phase I trial may be appropriate for some patients, especially when standard options are limited, while a phase III trial is usually more confirmatory and closer to regulatory decision-making.

 

Prevention, diagnostic, and screening trials

Not all clinical trials test treatments. Some are designed to prevent disease, detect it earlier, or improve diagnosis.

Prevention trials evaluate strategies that may reduce the risk of developing a disease. In cancer, this may include vaccines, medications, lifestyle interventions, or risk-reduction strategies in people with increased susceptibility.

Diagnostic trials study whether a test can detect or characterize a disease with greater accuracy. This may include blood biomarkers, imaging methods, molecular tests, pathology tools, or genomic profiling. Better diagnosis can help physicians select more appropriate therapies and avoid unnecessary interventions.

Screening trials evaluate whether a test can detect a disease early in people who do not yet have symptoms. In oncology, screening is important because early detection can improve treatment options and outcomes in certain types of cancer. However, these trials must also consider false positives, overdiagnosis, anxiety, costs, and whether early detection truly improves patient outcomes.

 

Supportive care and quality-of-life trials

Cancer care is not only about reducing tumor burden. It also seeks to help patients live better during and after treatment. Supportive care trials evaluate interventions that may reduce symptoms, manage side effects, improve nutrition, support mental health, control pain, reduce fatigue, improve sleep, or strengthen quality of life.

These studies are highly relevant because treatment success should not be measured only by imaging or laboratory results. A therapy that helps a patient feel stronger, tolerate treatment better, or maintain daily activities may have significant clinical value.

Supportive care trials may include pain management, exercise programs, psychological support, nausea control, integrative care approaches, survivorship interventions, or strategies to reduce treatment-related toxicity.

 

Figure 2. Clinical trial phases differ in duration, number of participants, study goals, and the type of evidence needed before regulatory review.

 

Randomized and non-randomized trials

One of the most important concepts in clinical research is randomization. In a randomized controlled trial, participants are randomly assigned to different study groups. One group may receive the investigational treatment, while another receives standard therapy, placebo, or another comparator treatment.

Randomization helps reduce bias. If physicians or participants chose the treatment group, the results could be influenced by factors unrelated to the therapy. Random assignment helps make groups more comparable, making it easier to determine whether differences in results are truly due to the intervention.

However, not all trials are randomized. Non-randomized trials may be used when randomization is not ethical, practical, or feasible. These studies can still provide useful information, especially in rare cancers or early-phase research, but their results must be interpreted carefully because they are more vulnerable to bias.

 

Blinding, placebo, and trial design

Some trials use blinding to reduce bias. In a single-blind study, the participant may not know which treatment they are receiving. In a double-blind study, neither the participant nor the research team evaluating the results knows the treatment assignment during the trial period. In some studies, triple blinding may also be used. In this design, in addition to the participant and the clinical or research team being unaware of the treatment assignment, the team responsible for data analysis or interpretation of the results may also remain blinded. The goal is to further reduce the risk of bias, especially when outcomes could be influenced by human expectations or subjective interpretations.

Blinding is not always possible. For example, it may be difficult to blind a surgical procedure, an image-guided intervention, or a treatment with evident side effects. Even so, when appropriate, blinding can strengthen the reliability of results.

Placebos are sometimes used in clinical trials, but in cancer they are handled with special care. In general, a placebo is not used instead of an effective standard treatment when a proven therapy exists. More commonly, a trial may compare standard treatment plus placebo against standard treatment plus an investigational therapy. This helps protect patients while allowing researchers to evaluate whether the new addition provides benefit.

Other designs include parallel trials, where each group receives an assigned treatment; cross-over trials, where participants may receive more than one treatment in sequence; and adaptive or sequential designs, where certain aspects of the trial may be modified based on accumulated data, following predefined rules.

 

Eligibility criteria: why not everyone can participate in every trial

Every clinical trial has eligibility criteria. These define who can and cannot participate. Criteria may include cancer type, stage, biomarkers, previous treatments, organ function, age, functional status, medical history, medications, and laboratory values.

Although eligibility criteria may feel restrictive, they serve important purposes. They protect patients from unnecessary risks and help researchers answer the study question clearly. For example, a trial testing a drug for a specific mutation must include patients whose tumors actually have that mutation. A trial involving a therapy metabolized by the liver may require adequate liver function.

Eligibility does not mean that a patient is “good” or “bad” for research. It means that the study must match their medical situation.

 

Informed consent and patient protection

Ethical clinical research requires informed consent. This is not simply a signature on a form. It is a process in which the patient receives understandable information about the study, including its purpose, procedures, possible benefits, risks, alternatives, privacy protection, and the voluntary nature of participation.

Patients have the right to ask questions, take time to decide, discuss the trial with their family or medical team, and withdraw from the study if they wish. Clinical trials are also reviewed and supervised by ethics committees, institutional review boards, sponsors, investigators, and regulatory authorities.

Good clinical practice emphasizes that the rights, safety, and well-being of participants must remain at the center of the study. Scientific progress matters, but it must never be placed above patient protection.

 

Why clinical trials are important for innovation in cancer

Many advances in cancer treatment exist because patients participated in clinical trials. Immunotherapy, targeted therapy, CAR-T therapy, modern radiation therapy strategies, precision diagnostics, and many supportive care interventions required structured clinical research before being widely used.

Clinical trials also help medicine move away from a one-size-fits-all approach. By integrating biomarkers, genomics, immune profiling, imaging, and patient outcomes, modern trials can identify which patients are more likely to benefit from a therapy and which may need a different strategy.

This is especially important in oncology, where two patients with the same type of cancer may have very different tumor biology. A clinical trial can help determine whether a treatment is appropriate for a particular molecular subtype, immune environment, or disease stage.

 

What patients should ask before considering a clinical trial

Patients who are considering a clinical trial should feel free to ask clear questions:

 

What is the purpose of this trial?

What phase is it in?

What treatment will I receive?

Will there be randomization?

Could I receive a placebo?

What are the known and unknown risks?

What are my other treatment options?

How often will I need appointments, imaging studies, or blood tests?

Who covers the costs related to the trial?

Can I continue my care with my current oncology team?

What happens if the treatment does not work for me?

 

These questions help patients make informed decisions and understand whether a study fits their values, goals, and medical situation.

 

A path from evidence to better care

Clinical trials are not just scientific procedures; they are the foundation of responsible medical progress. They help determine which treatments are safe, which are effective, which patients can benefit, and which approaches should not move forward.

For patients with cancer, a clinical trial may offer access to an emerging therapy, but it should always be considered carefully with a qualified medical team. Participation is voluntary, and not all trials are appropriate for all patients. The best decision is one that balances scientific rationale, patient safety, medical need, available evidence, and personal priorities.

Ultimately, clinical trials are the way oncology learns. They transform observation into evidence, evidence into standards, and standards into better care. Every well-designed trial contributes to a greater goal: improving the way cancer is detected, treated, managed, and understood.

 

Main Reference

Janiaud, P., Serghiou, S., & Ioannidis, J. P. A. (2019). New clinical trial designs in the era of precision medicine: An overview of definitions, strengths, weaknesses, and current use in oncology. Cancer Treatment Reviews, 73, 20–30. https://doi.org/10.1016/j.ctrv.2018.12.003 

 

Other References

Nair, B. (2019). Clinical trial designs. Indian Dermatology Online Journal, 10(2), 193–201. https://doi.org/10.4103/idoj.IDOJ_475_18 

Nathe, J. M., & Krakow, E. F. (2019). The challenges of informed consent in high-stakes oncology trials: A systematic review. MDM Policy & Practice, 4(1), 2381468319840322. https://doi.org/10.1177/2381468319840322