**6. Health-Related Quality of Life (HRQoL)**

WHO defines health as "A state of complete physical, mental, and social well-being not merely the absence of disease." The measurement of health and the effects of health care must include not only an indication of changes in the frequency and severity of diseases but also an estimation of well being and this can be assessed by measuring the improvement in the QoL related to health care [11].

HRQoL can be defined as self-perceived aspects of wellbeing that are related to or affected by the presence of a disease or treatment [12]. A multidimensional HRQoL instrument was defined as any quality of life instrument assessing two or more of the three core domains described by the World Health Association: physical, social, and psychological wellbeing [13]. As a multidimensional construct, it includes perceptions, both positive and negative, of several dimensions such as physical, emotional, social and cognitive functioning. It also includes the negative aspects of somatization disorder and symptoms caused by a disease and/or its treatment [14]. Studies undertaken in different settings or in different countries might display slight divergences as HRQoL is also modulated by cultural and care patterns.

Over the past 20 years there has been a growing interest in the inclusion of HRQoL measures to assess the effects of a condition and/or its therapies on a person's health. In response to this interest, methods to assess health status and HRQoL have proliferated. There are now a number of valid and reliable instruments available for use in research investigations, which are the culmination of years of research with various populations, and reflect the target populations' perceptions of their health status and HRQoL [15].

HRQoL-measurement instruments validated for use in cancer patients have two basic categories. Questionnaires specifically designed for the disease explore the repercussions of the most typical symptoms and side-effects and are appropriate for comparing different treatment modalities or changes in patients. The general instruments are applicable to any population and are better suited to studies that seek to ascertain the disease's repercussion on HRQoL, taking the general population as reference [16]. Among the former, the most used in Europe for MM patients are the European Organization for Research and Treatment of Cancer Core Cancer Quality Life Questionnaire (EORTC QLQ-C30) and its MM-specific module (EORTC-QLQ-MY24/MY20). Among the latter, the Medical Outcomes Survey Short-Form General Health Survey (SF-36) is the most widely used.

There are also symptom-specific instruments, assessing the patient's reflections directly concerning pain, fatigue, neuropathy and nausea.

For example, the Functional Assessment of Chronic Illness Therapy (FACIT) system which is an established, comprehensive set of health-related quality-of-life measures includes a 27-item general measure, the Functional Assessment of Cancer Therapy (FACT-G), which can be combined with disease or treatment-specific subscales. The FACT-G captures four domains of health-related quality of life: physical, social, emotional and functional well-being. The supplemental subscales measure additional concerns of a specific disease or treatment. For example, the multiple myeloma subscale (FACT-MM) includes MM-relevant items There are also symptom-specific measures, such as FACT-An for patients with anemia or fatigue, FACT-Bone Pain: for patients with bone pain and treatment-specific measures assessing the QoL changing due to treatment such as FACT&GOG-Ntx: for patients with neurotoxicity [17].
