Prevalence how common is fatigue in cancer

The simple answer to this question is 'very'. However, there are a number of important obstacles to determining the prevalence of fatigue in cancer patients. In part it is difficult to gain a reliable picture of the prevalence of fatigue in cancer because most studies which look at fatigue in cancer assess the symptom in special groups. Table 1.1 describes some of the factors which might lead to variation in rates of fatigue in cancer patients. It is likely that the prevalence of fatigue in cancer patients varies significantly according to site and type of cancer, stage of disease, presence of medical co-morbidity (anaemia, infection, metabolic disturbance), and psychiatric disorders (especially depression and anxiety).

Treatment is also likely to be a major contributing factor. Another problem in summarizing this growing literature is that a wide variety of different measures are used to assess fatigue and many of these are reported as continuous as opposed to binary outcomes. Whilst this reflects the continuous spread of fatigue within the population,

Table 1.1 Factors likely to affect the prevalence of fatigue reported in cancer patients

Disease factors

Stage of disease

Site of cancer

Type of cancer

Release of cytokines

Consequences of disease

Medical complications of cancer—anaemia, infection, metabolic

disturbance, malnutrition

Presence of psychiatric disorder—anxiety, depression etc.

Inactivity and deconditioning

Treatment factors

Radiotherapy

Chemotherapy

Surgery

Opiates

it makes the results difficult to interpret except to those familiar with the questionnaires involved.

Taking these considerations into account, Table 1.2 describes some of the studies which provide clear prevalence estimates of the symptom of fatigue. Apart from studies of survivors of lymphoma (Loge et al. 1999) it is hard to find any studies with prevalence estimates of fatigue, however defined, below 30%.

Some studies have assessed the prevalence of fatigue against other common symptoms: Ng and von Gunten (1998) found that fatigue and weakness were the two commonest symptoms in hospice patients, with a prevalence of over 80%, whereas pain was only present in approximately half. Despite the almost universal presence of fatigue in this population, it was relatively infrequently rated as the 'main symptom'— only being reported by 6%, as opposed to 11% for pain (the most common 'main symptom' was respiratory problems, present in 22%). Other studies which have assessed multiple symptoms also point to fatigue being the most common symptom of cancer irrespective of diagnosis or stage (Kurtz et al. 1994; Savage et al. 1997; Newell et al. 1998), except where the symptom was ascertained from case notes (Savage et al. 1997), implying that medical staff tend not to question patients about it, or ignore the symptom if it is spontaneously reported.

Relatively few studies have attempted to compare patients with cancer and other control populations: Mendoza et al. (1999) and Stone et al. (1999) (see Table 1.2) are exceptions and took healthy controls as comparison groups. Both studies found very significant differences in prevalence rates of severe fatigue between these groups. There can be little doubt that cancer is strongly associated with fatigue when healthy control populations are used. In contrast Andrykowski et al. (1998) compared levels of fatigue in 88 women with breast cancer and a similar number of women who had attended a breast clinic for benign breast disease. Whilst the women with breast cancer had more fatigue than those with benign disease the difference was slight and not statistically significant on several of the fatigue scales used. This may say more about their control group of symptomatic women consulting for a breast problem than about the cancer patients.

Two studies (Mendoza et al. 1999; Stone et al. 1999) looked at the distribution of fatigue among patients with cancer. In the general population the distribution is strongly skewed, with a long tail going to the right of the distribution. These studies indicate that the entire distribution is shifted to the right in cancer patients. Hence the increased prevalence of fatigue in cancer patients is not due to a relatively few sufferers who are very fatigued, but to a general shift in the population's experience of the symptom.

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