Cancer related quality of life is defied as "The extent to which a patient's biological, psychological and social well-being are affected by cancer or its treatment".
Quality of life is used as one measurement of the effects of treatment. It goes beyond the black and white definitions of 'cure' and 'local control' and 'mortality', and incorporates the effects of the treatment on the patient's wellbeing. Some cancer treatments are associated with significant toxicity which can be permanent and cause the patient physical, emotional or social distress. Examples include:
- Xerostomia after radiotherapy treatment for an oropharyngeal tumour
- Neurocognitive decline after chemoradiotherapy for CNS lymphoma.
- Peripheral neuropathy after cisplatin therapy
- Amputation of a limb for sarcoma
Without evaluation of quality of life, it may appear as though a treatment is highly successful; this treatment may have long term, non-fatal consequences for the patient.
When measuring quality of life and comparing it to survival for different treatments, several possibilities exist:
- A new treatment may have improved survival and similar or improved quality of life measures; this is the 'ideal' treatment and is easy to recommend
- A new treatment may have similar survival but improved quality of life; this treatment may still be worthwhile. This is sometimes seen in development of new drugs around a common theme; e.g. pazopanib may have better quality of life measures to sunitinib. It is often harder to justify using the newer therapy unless the cost is similar
- A new treatment may have worse survival but improved quality of life; this is rare situation but merits consideration
- A new treatment may have worse survival and similar or worse quality of life; this would not normally be recommended.
Most measurement tools are questionnaires that patients complete before, during and at set time periods after treatment on a clinical trial. Questions may relate to:
- Biological health (difficulty with mobiisation, physical symptoms such as nausea, xerostomia)
- Psychological health (mood)
- Social health (social interactions, family interactions)
There are general quality of life measures and disease specific measures, which may both be used for a single condition. The general questions usually detect global changes in quality of life, whereas specific questions focus on the commonly experienced problems for a particular diagnosis.
- For example, a breast cancer quality of life questionnaire may ask about breast pain (biological) and cosmetic outcomes (bio-pyscho-social), whereas a colorectal questionnaire could ask about continence (biological) and ability to attend social gatherings.
The most commonly quoted quality of life measure in cancer research is the EORTC QLQ-C30, which is a general questionnaire that can be supplemented by disease specific modules.
Quality of life is an inherently subjective measure and there are multiple factors which can influence a person's quality of life. Questions may be interpreted differently by people of different socioeconomic status or culture. External factors (such as job loss, marital breakdown) may impact significantly on quality of life in unexpected ways; if the life event was due to the cancer treatment then this is appropriate but it may skew results otherwise.
There is often difficulty with quantifying a difference in quality of life between two groups. If the questionnaire results suggest that patients having the new treatment score 2 points higher overall, what does this mean? Does it justify the costs of the new treatment? What dose a low score actually mean - is the patient's life completely intolerable?