Confidence, Not Knowledge, Drives Cancer Patients’ Willingness to Plan End-of-Life Care

For patients in the middle of cancer treatment, conversations about end-of-life care are among the hardest in medicine. Advance directives, the legal documents that record whether a person would want life-sustaining treatment withdrawn or continued when they can no longer speak for themselves, remain underused worldwide. Roughly one in three adults in the United States has completed any form of advance directive, and completion rates in many Asian countries are even lower, shaped by cultural norms around family decision-making and reluctance to discuss death openly. A new study from South Korea now offers a surprisingly clear answer to the question of what actually pushes patients with cancer toward signing these documents, and the answer is not what many clinicians might expect.

Researchers led by Ae Ri Kim of Soonchunhyang University Seoul Hospital, together with Kisook Kim and Hyohyeon Yoon of Chung-Ang University, surveyed 200 patients actively receiving cancer treatment and modeled their intention to complete an advance directive using the extended theory of planned behavior, a widely used psychological framework for predicting human action. Published in Supportive Care in Cancer, the study found that three classic psychosocial variables, attitude toward the behavior, subjective norm, and perceived behavioral control, together explained a striking 74.1 percent of the variance in intention. Of these, perceived behavioral control, the patient’s own sense of confidence and ability to carry out the task, emerged as the single strongest predictor.

The theoretical scaffolding of the study is worth unpacking, because it explains why the result matters. The theory of planned behavior, developed by Icek Ajzen in the 1980s from earlier work with Martin Fishbein, holds that the most immediate determinant of any deliberate behavior is the intention to perform it. Intention, in turn, is shaped by three forces: attitude, meaning whether the person evaluates the behavior positively or negatively; subjective norm, meaning the perceived social pressure from important others to perform or not perform it; and perceived behavioral control, meaning how easy or difficult the person believes the behavior would be. When researchers extend the model, they add factors thought to be relevant to a specific behavior, testing whether they add explanatory power beyond the classic trio.

In this study, the extension took two forms. The researchers measured patients’ knowledge about advance directives, reasoning that people who understand what the documents do might be more inclined to complete them, and they measured cancer-related fatigue, the profound and pervasive exhaustion that affects a large majority of people undergoing treatment. Fatigue was a plausible candidate because completing an advance directive requires cognitive effort, attention, and the physical and mental energy to engage in difficult conversations, all of which are diminished in severely fatigued patients. The team used hierarchical multiple regression, entering the variables in three steps: first attitude and subjective norm, following the earlier theory of reasoned action; then perceived behavioral control, completing the theory of planned behavior; and finally knowledge and fatigue, producing the extended model.

The results were decisive at each step. Attitude and subjective norm alone were significant predictors of intention. Adding perceived behavioral control substantially improved the model, and it dominated as the strongest single effect. But knowledge and cancer-related fatigue, the two extension variables, failed to reach statistical significance. In other words, knowing more about advance directives did not, by itself, make a patient more likely to intend to complete one, and the crushing tiredness of cancer treatment did not measurably erode the intention either. What mattered was whether patients felt capable of the process and believed the people around them supported it.

This pattern carries a pointed message for clinical practice. Many educational campaigns about advance care planning are built on the assumption that information is the bottleneck, that if patients simply understood the documents better they would sign them. The South Korean findings suggest that this assumption is at least incomplete. A patient can know exactly what an advance directive is, what it covers, and how to file it, yet still feel unable to navigate the emotional terrain of the decision, uncertain how to raise the topic with family members, or unsure whether the healthcare system will honor their choices. Perceived behavioral control captures precisely this gap between knowing and doing.

The authors argue that the practical implication is to strengthen patients’ confidence and ability to engage in advance care planning, rather than simply delivering more facts. Structured counseling and tailored education should begin early in the treatment process, they conclude, so that decisions about end-of-life care can unfold at a pace that reflects the patient’s values and preferences rather than being forced by a crisis. Interventions that build positive attitudes, foster supportive norms among family and clinicians, and give patients a concrete sense of control over the process may together move intention, and ultimately behavior, more effectively than information alone.

The South Korean context adds an important layer to the interpretation. In many Asian healthcare settings, end-of-life decisions have traditionally been made collectively, with families often shielding patients from full information about their prognosis and relatives frequently serving as the primary decision-makers. Korea has moved rapidly in recent years to formalize advance directives for life-sustaining treatment, establishing a national infrastructure through its life-sustaining treatment decision system, yet cultural hesitancy around discussing death persists. That subjective norm remained a significant predictor in this sample underscores how much social context shapes these intentions, and it suggests that interventions must engage families, not just patients, to be effective.

The study has limits worth noting. It measured intention rather than actual completion of advance directives, and intention, while the best-established psychological proxy for behavior, does not always translate into action. The sample of 200 patients at a single institution, assessed with structured questionnaires, cannot capture every factor that might matter, and the cross-sectional design shows association rather than causation. The researchers also note that the data are not publicly available for ethical reasons. Still, an explained variance of 74.1 percent is unusually high for behavioral research, indicating that the theory of planned behavior framework captures most of what drives these decisions in this population.

What makes the finding resonate beyond oncology is its generality. Across domains as varied as vaccination uptake, organ donation, and health screening, perceived behavioral control has repeatedly proven to be one of the most powerful levers in the theory of planned behavior, and this study extends that pattern to one of medicine’s most emotionally charged decisions. For the growing number of health systems trying to normalize advance care planning, the lesson is concrete: build the patient’s sense of agency. Give people a structured, supported path to the signature, involve the people they trust, and start the conversation while they are well enough to lead it. Confidence, it turns out, may be the missing ingredient between a form that exists and a form that gets signed.

Subject of Research: Psychosocial predictors of advance directive completion intention among cancer patients undergoing treatment

Article Title: Intention to complete advance directives among patients with cancer undergoing treatment: application of the extended theory of planned behavior

Article References: Kim, A. R., Kim, K., & Yoon, H. (2026). Intention to complete advance directives among patients with cancer undergoing treatment: application of the extended theory of planned behavior. Supportive Care in Cancer, 34(10), Article 1047. https://doi.org/10.1007/s00520-026-11272-y

Image Credits: AI Generated

DOI: 10.1007/s00520-026-11272-y

Keywords: advance directives, advance care planning, theory of planned behavior, cancer patients, perceived behavioral control, end-of-life care, palliative care, subjective norm, cancer-related fatigue, South Korea, behavioral intention, supportive care