Hello, my name is Costanza Di Patrizi, PhD candidate at Antwerp University in Belgium. In the previous blog post, we discussed why it is important to integrate patients’ perspectives into research and clinical practice: because the experience of illness cannot simply be inferred from the outside, because patients have a legitimate role in decisions that affect their lives, and because the way illness is experienced may, in some cases, also be associated with clinical outcomes. But what do we actually mean when we talk about quality of life (QoL)?
The concept of QoL is relatively recent:
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- It began to emerge in scientific debate around the 1940s. Before then, a person was generally considered healthy simply if they were not ill.
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- A widely referenced definition was proposed by the British physician Kenneth Calman in 1984, who described QoL as the gap, at a given point in time, between an individual’s hopes and expectations and their present experience. From this perspective, QoL is an inherently dynamic concept and difficult to measure. It does not represent an objective and stable state, but varies over time, depends on circumstances, and can only be understood from the perspective of the person experiencing it.
- In similar terms, Revicki and colleagues (2000) define QoL as the set of subjective experiences, states, and perceptions related to overall well-being. This definition reinforces the central role of subjectivity, while also pointing to the influence of personal values, social context, and living conditions. For this reason, some authors have suggested reconsidering the concept itself. Kyriacou, for example, suggests that it may be more accurate to speak of “quality of THEIR life”, to emphasize that what is being assessed is always someone’s QoL, rather than an abstract condition defined from the outside.
From quality of life to health-related quality of life
From the 1980s onward, with the expansion of clinical research and studies on treatment outcomes, a more specific concept began to take shape: health-related quality of life (HRQoL). While QoL is a broad concept referring to a person’s overall well-being, HRQoL focuses on those aspects of life that are directly influenced by health, illness, medical treatments, and the functioning of healthcare systems.
The U.S. Food and Drug Administration (FDA) defines health-related quality of life as a multi-domain concept representing a patient’s general perception of the effect of illness and treatment on physical, psychological, and social aspects of life. Over the years, many similar definitions have been proposed. Karimi and Brazier (2016), for example, describe HRQoL as a multidimensional construct reflecting the impact of health status on a person’s ability to live a full and satisfying life.
Despite some differences in terminology, there is broad agreement on one point: HRQoL is inherently multidimensional. It generally includes at least three major domains:
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- physical well-being, including symptoms, pain, fatigue, and functional limitations
- psychological well-being, including anxiety, depression, coping strategies, and concerns related to illness
- social well-being, including relationships, social participation, and family or work roles
In oncology, a fourth domain is often considered: functional well-being, referring to a person’s ability to perform everyday activities and maintain independence.
In recent years, growing attention has also been paid to less traditional but equally relevant dimensions, such as the economic and financial impact of illness. The concept of financial toxicity, for example, describes the economic burden that cancer care can place on patients and their families, with potential consequences for QoL. Considering these dimensions together provides a more comprehensive understanding of how illness affects people’s lives.
Why quality of life is central in oncology
When we think about cancer treatment, the first question that often comes to mind is whether the treatment works. But for patients, another question can be just as important: how will my life change?
In recent decades, advances in early diagnosis, treatment, and supportive care have significantly improved survival for many types of cancer. As a result, a growing number of people now live for many years with or after a cancer diagnosis, and the evaluation of treatment outcomes can no longer focus exclusively on survival or disease control. A cancer diagnosis and its treatments can reshape everyday life in multiple ways, affecting not only physical well-being but also emotional balance, social roles, and future expectations. Patients may have to adapt to persistent symptoms, ongoing uncertainty, and repeated medical follow-up, all of which can influence how they perceive their health and their lives more broadly. For these reasons, QoL is now considered a key outcome in oncological research and in the evaluation of health technologies.
How quality of life can be measured
Because quality of life is inherently subjective, the most reliable way to measure it is by collecting the patients’ perspectives directly.
Over the past decades, numerous assessment tools have been developed, known as Patient-Reported Outcome Measures (PROMs), which are now considered the standard for measuring QoL in clinical research. PROMs are standardized questionnaires through which patients directly report information about their health status, symptoms, daily functioning, and perceived well-being, without the intermediate interpretation of a clinician.
Along with PROMs, Patient-Reported Experience Measures (PREMs) have also been introduced. Unlike PROMs, these instruments do not focus on health outcomes but on patients’ experiences with healthcare services – for example the quality of communication with healthcare professionals, access to care, or the coordination of services.
The growing use of these instruments reflects an important shift in how healthcare systems are evaluated: alongside traditional clinical indicators, it has become increasingly important to measure how patients experience illness and the care they receive.
Over time, many questionnaires have been introduced to measure QoL:
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- Some instruments are generic, meaning they can be applied across different health conditions. These include the WHOQOL questionnaires developed by the World Health Organization, which explore different aspects of people’s everyday lives.
- Other instruments focus more specifically on HRQoL. Widely used examples include the SF-36 (Short Form Health Survey), which assesses multiple dimensions of physical and mental health, and the EQ-5D-5L, commonly used in economic evaluations and health technology assessment, as it describes health status across five key dimensions and allows the calculation of indicators for cost-utility analyses.
- In oncology, additional instruments have been created to capture aspects particularly relevant to cancer patients. The FACT-G (Functional Assessment of Cancer Therapy – General) is part of the broader FACIT (Functional Assessment of Chronic Illness Therapy) system, a family of questionnaires designed to assess QoL across a range of chronic conditions, including many types of cancer. Another well-established instrument is the EORTC QLQ-C30, developed by the European Organization for Research and Treatment of Cancer (EORTC). This questionnaire includes thirty items covering different aspects of physical, emotional, cognitive, and social functioning, as well as a set of symptoms commonly associated with cancer. These instruments can also be complemented by disease-specific modules: in the case of esophageal cancer, for example, the EORTC QLQ-OES18 module assesses symptoms and difficulties specific to this condition, such as swallowing problems or limitations related to eating.
- More recently, systems such as PROMIS (Patient-Reported Outcomes Measurement Information System), created by the U.S. National Institutes of Health, have introduced new approaches to measuring patient-reported outcomes through item response theory and computer-adaptive testing, allowing for more flexible and tailored assessment.
- Finally, it is worth noting that broader QoL (and HRQoL) measures do not capture all aspects of patients’ experiences. For this reason, more focused instruments are often used to assess specific dimensions, particularly in oncology. These may target, for example, anxiety, depression, or fear of cancer progression. Scales such as the Hospital Anxiety and Depression Scale (HADS) or the Cancer Worry Scale capture concerns that are only partially reflected in general QoL measures.
Some limitations of the concept
Despite its widespread use in research and clinical practice, the concept of quality of life also presents several theoretical and methodological limitations.
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- A first issue concerns the strong subjective component of QoL. While this is one of its main strengths – because it captures the patient’s perspective – it also makes measurement and comparison across individuals or populations more complex. QoL depends on expectations, coping strategies, and personal values, which may change over time and vary significantly across social and cultural contexts.
- A second aspect concerns how QoL is operationalized in measurement tools. Standardized questionnaires allow researchers to collect comparable data, but they inevitably select certain dimensions of human experience while leaving others aside. In this sense, quality-of-life measures also reflect theoretical choices about what is considered relevant to people’s well-being.
- The literature has also pointed out that many quality-of-life measures tend to prioritize individual and psychological dimensions of well-being, while broader structural factors – such as social inequalities, working conditions, or access to resources – may have an equally significant impact on how illness is experienced.
For these reasons, QoL remains an evolving field of research, in which quantitative instruments are increasingly combined with qualitative approaches in order to gain a more comprehensive understanding of patients’ experiences of illness and care.
Costanza