2. Assessment of Functional Decline
Functional decline is typically assessed through a direct measure of an individual’s capacity to independently fulfil their activities of daily living (ADLs)
[1]. ADLs are typically categorised as either basic (tasks required for normal day-to-day functioning), or instrumental (tasks that are not necessarily essential but allow for one to live independently). Basic ADLs include tasks such as ambulation, eating, dressing, toileting, and personal hygiene. Instrumental ADLs are typically more complex and include managing finances, shopping, transportation, home maintenance, communication, and managing medications
[7].
It should be noted that frailty, typically defined as a “state of reduced physiologic reserve”, is not synonymous with functional decline, although the two frequently measure domains which overlap
[8][9][10]. Frailty is a broader concept than functional decline and measures vulnerability to functional decline as opposed to functional decline itself—its clinical utility therefore lies in its ability to predict susceptibility to disability
[11]. While functional decline can be observed through the assessment of ADLs, frailty is often initially clinically silent. Its development can instead be identified through markers such as nutritional status, physical activity, mobility, energy, strength, cognition, mood, and social support. In this regard, the assessment of frailty requires a more comprehensive ‘geriatric assessment’ beyond the assessment of ADLs
[8]. The Fried frailty phenotype is typically considered to be the gold-standard definition for the measurement of frailty and defines it as the presence of three or more of the following: unintentional weight loss (at least 10 pounds/4.5 kg in the past year), weakness (grip strength in the lowest quintile adjusted for sex and body mass index), slowness (walking time in the lowest quintile adjusted for sex and height), a low level of physical activity, and self-reported exhaustion
[12]. Frailty is certainly seen at greater rates in patients with cancer
[13][14][15].
There are several measures of functional status that can be used in older patients with cancer; these tools are summarised in
Table 1. These include instruments such as the Barthel index, the Eastern Cooperative Oncology Group performance status (ECOG), the Katz index of independence in activities of daily living scale (ADL), the Instrumental Activities of Daily Living Scale (IADL), the Rosow–Breslau health scale, and the Karnofsky performance status scale (KPS)
[8][9][10]. Performance status, measured by an assessment of ECOG scores (0–4) is particularly relevant in oncology and is often used to measure suitability for anti-cancer treatment
[16]. Physical performance measures such as the Timed Up and Go test (TUG), grip strength, 6-min walk test (6MWT), and gait speed can be used as surrogate markers of functional status as physical strength is often necessary to perform ADLs (e.g., adequate grip strength is required for personal care) although this is not always the case, given that some level of function can be maintained in the presence of poor physical performance
[8][9][10][17]. The benefit of physical performance measures, however, lies in their measurement requiring direct observation rather than self-report, providing a more objective measure of a patient’s function.
The comprehensive geriatric assessment (CGA) is a more holistic alternative to the above tools that assesses several domains, including medical conditions, medications, nutritional assessment, cognitive status, mental health, social circumstances, environment, and functional status. Given the variety of domains it assesses, the CGA provides a broader overview of older patients with cancer and captures their susceptibility to further decline, as opposed to solely assessing functional status. The CGA bears particular clinical relevance having been recommended by the American Society of Clinical Oncology (ASCO) for assessing frailty in patients over 65 years of age receiving chemotherapy
[8][18]. Other tools that provide a broader assessment of older patients and have been validated in cancer cohorts include the 36-item short form survey (SF-36; a quality-of-life assessment)
[19], Geriatric 8 (G8)
[20], Vulnerable Elders Survey-13 (VES-13)
[20], Fried frailty criteria
[21][22], Senior Adult Oncology Program 2 tool
[23], Groningen Frailty Indicator (GFI)
[21], and Rockwood Clinical Frailty Scale
[21]. Of these, Garcia et al. recommend the G8 for screening older patients with cancer, given a high level of evidence supporting its sensitivity and specificity when screening for vulnerabilities
[20] although it is noted that this tool is a screening measure that provides a less comprehensive view of a patient’s holistic health and is instead meant to identify patients who require further assessment using a more detailed tool. The authors recommended the VES-13 as an effective screening alternative in resource-poor settings
[20]. The Cancer and Aging Research Group (CARG) also provides an online assessment tool for clinicians that combines the KPS scale, TUG, and Blessed Orientation–Memory–Concentration test (a cognitive function assessment aimed at assessing the contribution of cognitive decline on functional ability)
[24]. These geriatric assessments tend to provide not only an indication of declines in ADLs, but also frailty and the susceptibility of a patient to future disability.
Table 1. Tools that can be used to assess functional status in older patients with cancer.
4. Mechanisms Driving Functional Decline
The development of functional decline in patients with cancer is likely multifactorial, with shared risk factors, social factors, comorbidities, tumour-related factors, and treatment all playing a role. In older adults, functional decline is likely to already be occurring as a normal consequence of ageing, irrespective of a cancer diagnosis, with the rate of functional decline generally steepening with increasing age
[2]. Buchner et al. describes an accelerated ageing model that can be easily applied to the functional decline seen in older adults with cancer (
Figure 1). Here, patients slowly lose function as they age, with poor lifestyle behaviours and acute insults, such as cancer and anti-cancer treatment, accelerating this process. This decline can be tolerated while the patient has ‘physiologic reserve’, the capability of an individual to tolerate stressors, until they reach a point at which functional disability occurs. This model recognises the slow decline of function over the lifespan and acknowledges that acute insults, such as cancer, are not the sole drivers of functional impairment in older patients with cancer, but instead, accelerate a pre-existing decline.
Figure 1. An “Accelerated Ageing” model of functional decline
[11].
While some of these represent cancer- and treatment-related factors, the role of shared risk factors in functional decline in older patients with cancer must be acknowledged. For example, smoking is a strong risk factor for lung function decline
[64] and has an adverse impact on functional status irrespective of cancer status
[65]. Given that smoking is strongly associated with a number of cancer types, with nearly 80% of lung cancers being caused by smoking
[66], older patients with cancer with a smoking history may have experienced smoking-related functional decline, regardless of their cancer diagnosis or treatment. These patients may also have concomitant smoking-related lung disease, such as chronic obstructive pulmonary disease, a condition independently linked with poorer functional status
[67]. Obesity, another significant risk factor for cancer, particularly in older, post-menopausal women
[68], can independently accelerate functional decline
[69].
Some of the predictors of functional decline in patients with cancer, both cancer- and non-cancer related, are described in Table 2. Note that each factor may not predict functional decline across all cancer types and demographics although many are relevant to the general older cancer-survivor population.
Table 2. Factors that may predict functional decline in older patients with cancer.
Several tumour-related factors can contribute to functional decline although this varies between cancer types. In patients with primary lung cancer or multiple lung metastases, for example, the replacement of lung volume and subsequent reduction in pulmonary function can adversely impact functional status
[72]. Patients with primary or secondary brain malignancies can experience disability in function due to motor or sensory deficits
[73]. Similarly, patients with metastatic spinal cord compression are often afflicted by functional deficits
[74]. In cancers not impeding on organ structures, tumour-related symptoms such as pain, fatigue, and depressive symptoms are likely to be the primary driving mechanism in functional impairment
[75]. This may be particularly common in haematological malignancies, considering the prevalence of anaemia and its subsequent impact on a patient’s energy levels
[76]. Given that as many as 38% of patients with cancer report moderate-to-severe pain, with fatigue and depressive symptoms being similarly common, recognising the impact of such symptoms plays an important role in any comprehensive assessment of functional status
[77].
Cancer treatment is likely to be the main contributing factor to functional decline in patients with cancer, with exact mechanism varying between treatment modalities. Across all treatment types, fatigue is a common symptom that can result in functional deficits; prevalence estimates of fatigue during treatment can be anywhere from 25% to 99%, with up to one-third experiencing fatigue for as many as 10 years post-cancer diagnosis
[78]. Chemotherapy-related toxicity is also incredibly common. Common toxicities, such as nausea and vomiting, diarrhoea, anaemia secondary to myelosuppression, peripheral neuropathy, vestibular dysfunction, weakness, and fatigue, are all likely to be drivers of functional impairment
[79][80][81]. Hormonal therapy can have similarly debilitating side effects: In patients receiving androgen deprivation therapy for prostate cancer, for example, weakness and muscle wasting is common
[82]. More targeted treatment modalities, such as radiotherapy, are likely to have less impact on functional status than their systemic counterparts. The nature of radiotherapy toxicity is both site- and dose-dependent but can result in complications such as cardiac toxicity limiting exercise tolerance, mucositis impacting personal care and eating, and fatigue that can have a pervasive impact on ADLs, although the latter two tend to be acute and resolve shortly after treatment
[83]. Similarly, surgery is less likely to cause persistent functional impairment in older patients with cancer, with most patients returning to baseline functional status within months after an operation
[60]. However, patients with post-operative complications and a prolonged length of hospital stay can suffer from accelerated bone loss, malnutrition, cognitive decline, and deconditioning, all factors that can independently contribute to declines in function post-discharge
[84].