Prevalence of Substance Abuse Disorders in Cancer Patients

ABSTRACT: Drug abuse presents a complex set of physical and psychosocial issues that complicate cancer treatment and pain/symptom management. Most oncologists are not be well versed in either the conceptual or practical issues related to addiction. As a result, they often struggle in their attempts to effectively treat patients who are or have been substance abusers, and they find it difficult to understand issues of addiction in patients with pain who have no history of substance abuse. In the first installment of a two-part series, the authors explore the epidemiology of substance abuse. An examination of the distinctions between abuse and dependence leads to definitions of these terms appropriate for the oncology setting. Guidelines for assessing aberrant drug-taking behavior are also offered. Part 2, which will appear in the next issue of oncology, will discuss the clinical management of cancer patients with a history of substance abuse.[ONCOLOGY 12(4): 517-521, 1998]

Drug usage is surprisingly common in this country, as indicated by statistics showing that almost one-third of the US population has used illicit drugs, and an estimated 6% to 15% have a substance-use disorder of some type.[1-3] The prevalence of drug use in this country and its association with life-threatening diseases, such as AIDS, cirrhosis, and some types of cancer,[4] ensures that problems related to abuse and addiction will be encountered in oncology settings.

Drug abuse (current or even a remote history) presents a complex set of physical and psychosocial issues that complicate cancer treatment and pain/symptom management. Oncologists are generally not well versed in either the conceptual or practical issues related to addiction; thus, they struggle in their attempts to treat these patients effectively, and they find it difficult to understand issues of addiction in patients with pain who have no history of substance abuse. In this article, we will examine important conceptual and clinical aspects of addiction that can lead to better care of these challenging patients.

Defining the Goals of Care

Concerns central to planning overall treatment of pain and cancer vary with the patient’s addiction status. It is important to appreciate the extremely heterogeneity of patients with a history of abuse or addiction. Patients who are actively abusing illicit drugs, alcohol, or prescription drugs pose clinical problems distinct from patients in drug-free recovery and those in methadone maintenance programs.

Although these distinctions are useful, they still oversimplify the variations within these populations, which can be further complicated by the issues of which drugs they use and at what frequency. In addition, drug abuse varies over time; appropriate diagnosis of the patient may be complicated by this fluctuation and by other changes in comorbid physical and psychosocial factors that influence drug use. Certain changes in drug-taking behavior are inherent to cancer illness and treatment and are accompanied by the development of related psychological and physical symptoms.

The range of clinical problems presented by patients with substance-abuse histories is diverse. Clinicians must monitor and control drug use in all patients, a precaution often neglected in those who are not substance abusers. This becomes a substantial task in the treatment of active abusers, in addition to the complexity of treating cancer in such patients.

In some cases, compliance with treatments for cancer may be so poor that the substance abuse actually shortens life expectancy by preventing the effective administration of oncologic therapy. Outcomes may also be altered by the use of drugs in a manner that negatively interacts with therapy or predisposes patients to other serious morbidity. Defining the goals of care can be very difficult when patients’ poor compliance contradicts their stated desire for cancer treatment.

The stress of cancer, in addition to the impact of unchecked substance abuse, can weaken an already fragile social support network. Such a network would ordinarily be crucial for coping with the chronic stressors associated with cancer and its treatment.

One important source of support is the patient’s relationships with members of the treatment team. Concerns about drug abuse may undermine the doctor-patient relationship and lead clinicians to doubt the veracity of the history, the report of symptoms, and compliance with therapy. Clinicians are usually unwilling to confront this issue. This avoidance reduces the opportunity for resolution and further undermines the therapeutic alliance with the staff.

Patients with a history of substance abuse often come from backgrounds characterized by exploitation and neglect. They are frequently distrustful, may question the team’s good will, and sometimes harbor negative expectations that become self-fulfilling prophesies. Wariness about the doctor-patient relationship can lead to disruption of assessment, management, and follow-up, resulting in the failure of therapies intended to improve quality of life. If illicit drug use or manipulative behavior occurs, extraordinary efforts by the treatment team may be required to avoid a vicious cycle of undertreatment, drug abuse, and diminished trust.

Epidemiology

Few studies have evaluated the epidemiology of substance abuse in patients with cancer and other progressive medical illnesses. Although prevalent in the general population, substance abuse appears to be fairly rare within the large tertiary-care population with cancer. In 1990, only 3% of inpatient and outpatient consultations performed by the Psychiatry Service at Memorial Sloan-Kettering Cancer Center were requested for management of issues related to drug abuse. This indicates that concerns about substance abuse on the part of referring oncologists were lower than the prevalence of these problems in society at large, in general medical populations, and in emergency medical departments.[1-3,5,6]

This low prevalence was also reported in the Psychiatric Collaborative Oncology Group study, which assessed psychiatric diagnoses in ambulatory cancer patients from several tertiary-care hospitals.[6] Based on structured clinical interviews, less than 5% of a large sample of ambulatory cancer patients met the criteria for a substance-use disorder outlined in the third edition of the Diagnostic and Statistical Manual for Mental Disorders (DSM-III).[7]

For several reasons, the low prevalence of drug abuse in cancer center populations may not be representative of the true prevalence in the cancer population overall. First, there is no compelling reason to think that age-corrected substance abuse rates would be lower in people with cancer than rates in the normal population (ie, having cancer does not somehow protect against substance abuse). Also, the relatively low prevalence of substance abuse among cancer patients treated in tertiary-care hospitals may reflect institutional biases or a tendency for patient underreporting in these settings.

Furthermore, many drug abusers are poor and therefore may feel alienated from the health-care system; consequently, they often do not seek care in tertiary-care centers. Finally, even those who are treated in these centers may not acknowledge drug abuse for fear of stigmatization. In support of this assertion, a recent survey of patients admitted to a palliative-care unit uncovered findings indicative of alcohol abuse in approximately 20%.[8]

Thus, the epidemiology of substance abuse in cancer patients remains largely unstudied and needs of clarification.

Defining Substance Abuse and Addiction

It is difficult to define substance abuse and addiction in cancer patients since the terms have been developed from addict populations without medical illness. However, both epidemiologic studies and clinical management depend on an accepted, valid nomenclature for substance abuse and addiction.

For example, the pharmacologic phenomena of tolerance and physical dependence are commonly confused with abuse and addiction (Table 1). The use of diagnostic terms is also strongly influenced by sociocultural considerations, which may lead to confusion in the clinical setting. Clarifying this terminology is an essential step toward improving the oncologist’s ability to diagnose and manage substance abuse.

Tolerance and Physical Dependence
Tolerance and physical dependence can occur during long-term therapy with opioids and other drugs. These phenomena must be distinguished from abuse and addiction. Tolerance is a pharmacologic property defined by the need for increasing doses to maintain effects.[9,10] Clinicians and patients commonly worry that tolerance to analgesic effects may compromise the benefits of therapy (ie, pain medication will not work when it is “really needed”). They are concerned that tolerance may lead to progressively higher, and ultimately unsustainable, doses (as if addiction and dose are associated).

Compounding the confusion, the need to increase doses to regain pleasurable effects has been speculated to be an important element in the etiology of addiction.[11] Extensive clinical experience with opioid drugs in the medical context demonstrates that tolerance does not cause substantial problems.[12-14] Furthermore, clinical observation of addicts fails to support the conclusion that analgesic tolerance contributes to the development of addiction. Physically healthy addicts may or may not have any of the manifestations of analgesic tolerance, while the opioid-treated cancer patient who develops analgesic tolerance typically does so without evidence of abuse or addiction.

Physical dependence is defined as the occurrence of an abstinence syndrome (withdrawal) following abrupt dose reduction or administration of an antagonist.[9,10,15] The duration of administration and dose of opioids that produce clinically significant physical dependence are unknown. Many pain experts assume that the potential for withdrawal exists after opioids have been administered repeatedly for as brief a period as a few days. In the clinical setting, physical dependence to an opioid is not a significant problem as long as patients are instructed to taper the dose when discontinuing therapy.

There is great confusion among clinicians about the differences between physical dependence and addiction. Physical dependence has been suggested as a component of addiction.[16,17] Theories of addiction indicate that drug-seeking behaviors are reinforced by the avoidance of withdrawal symptoms.[11] Clinical experience in patients with chronic nonmalignant pain indicates that the uncomplicated discontinuation of opioids is routine, even in physically dependent patients.[18] In oncology settings, doses of opioids are easily tapered in cancer patients whose pain has been relieved by effective antineoplastic therapy.

These definitions of tolerance and physical dependence highlight deficiencies in the current psychiatric nomenclature for substance abuse. The terms “addiction” and “addict” are especially problematic. These nonpsychiatric labels are often misapplied to describe both aberrant drug use (reminiscent of the behaviors that characterize active abusers of illicit drugs) and tolerance or physical dependence. Clinicians sometimes use the word “addicted” to describe compulsive drug-taking in one patient and nothing more than the possibility for withdrawal in another.

Thus, patients, families, and staff become very concerned about the outcome of opioid treatment when this term is applied. The mere capacity for withdrawal should never lead to use of the terms “addict” or “addiction.” These patients should be referred to as “physically dependent.”

Substance Abuse vs Substance Dependence
The actual psychiatric terminology codified in the DSM-IV is also very problematic.[17] The DSM-IV does not include the term “addiction” but, instead, describes two types of substance use disorders: substance abuse and the more serious substance dependence. Substance abuse focuses on the psychosocial, physical, and vocational harm that stems from drug-taking. This criterion requires substantial refinement in cancer patients taking opioids for pain (see below).

The DSM-IV criteria for substance dependence highlight chronicity and criteria based on physical dependence and tolerance. As mentioned above, the criteria for tolerance and physical dependence are inappropriate in the medically ill. Thus, the existing terminology can complicate the effort to characterize and communicate about the drug-taking behavior of a patient with a medical illness that is appropriately treated with a potentially abusable drug that causes tolerance and physical dependence.

Other concerns compound these problems of inappropriate terminology. The problems of undertreatment, sociocultural influences on the definition of aberrance in drug-taking, and cancer-related variables increase the difficulty in assessing and communicating about patients’ drug-taking behavior.

Pseudoaddiction
There is compelling evidence that pain is undertreated in populations of medically ill patients, including those with cancer and AIDS.[19,20] Clinical experience suggests that inadequate pain/symptom management can be a trigger for aberrant drug-related behaviors. The term “pseudoaddiction” was coined to describe the distress and drug-seeking that can occur in the context of unrelieved cancer pain.[21] The key feature of this syndrome is that the aberrant behaviors cease when effective analgesia is administered.

The possibility of pseudoaddiction poses a challenge for the assessment of known substance abusers who develop cancer pain. Clinical experience suggests that aberrant behaviors driven by unrelieved pain can be particularly dramatic in this population (eg, using street drugs for pain control). Some patients adopt less obvious patterns of behavior (such as intense drug-seeking from prescribers or escalating doses unilaterally) that also generate concerns about the possibility of true addiction. Although it may be clear that drug-related behaviors are aberrant, the meaning of these behaviors may be difficult to discern in the context of unrelieved symptoms.

Distinguishing Aberrant Behavior
Sociocultural factors influence the understanding of drug-taking as well. By definition, the use of an illicit drug, or the use of a prescription drug without a medical indication, is abuse. Any drug used in a compulsive manner or continually used despite harm to the user or others merits consideration of a diagnosis of addiction. These definitions are derived from social and cultural norms of drug-taking. Because drug-taking norms are not clearly known for prescription medications used for legitimate medical purposes, there is less certainty about the behaviors that could be characterized as aberrant.

Although the aberrance of some behaviors would not be argued despite the lack of such norms, such as selling prescription drugs or the intravenous injection of an oral formulation, many other behaviors are less obvious. For example, is it aberrant for the patient with unrelieved pain to take extra doses of a prescribed opioid, particularly if this behavior was not specifically proscribed by the clinician? Is it aberrant to use an opioid drug for insomnia?

These less obvious behaviors are not clearly outside social or cultural norms. In everyday practice, there is little certainty about the parameters of normative drug-taking behavior. In the area of prescription drug use, there are no empiric data that define these parameters. If a large proportion of patients were discovered to engage in a specific behavior , it is essentially normative and judgments about deviance should be influenced accordingly.

This issue was recently highlighted in a pilot survey performed at Memorial Sloan-Kettering Cancer Center. This survey revealed that 26% of cancer patients admitted borrowing an anxiolytic from a family member at some time. The relatively high prevalence of this behavior among cancer patients raises questions about its predictive validity as an indicator of any diagnosis related to substance abuse.

There is a need for empiric data that illuminate the prevalence of drug-taking attitudes and behaviors in different populations of pain patients (ie, those with cancer, AIDS, sickle cell anemia, and chronic noncancer pain) to help guide clinical thinking about behaviors that emerge during treatment.

Use Despite Harm
Changes induced by cancer as a progressive disease challenge the core concepts used to define addiction. Harm done to physical or psychosocial functioning by cancer and its treatment may be difficult to separate from morbidity associated with drug use. This may particularly complicate efforts to evaluate the concept of “use despite harm,” which is critical to the diagnosis of addiction.

For example, the effects of questionable drug-related behaviors can be difficult to discern in the patient who develops social withdrawal or cognitive changes following brain irradiation for metastases. Even if impaired cognition is clearly related to pain medication in this scenario, this effect might only reflect a narrow therapeutic window, rather than the patient’s use of an analgesic to achieve these psychic effects.

Translation of the use despite harm construct is usually required in the assessment of drug-related behaviors in patients with advanced cancer. “Harm” should be specifically assessed within the context of medical treatment. Thus, the presence of mild mental clouding or the time spent out of bed may be less meaningful than other outcomes, such as noncompliance with primary therapy related to drug use, and behaviors that jeopardize relationships with physicians, other providers, or family members.

Defining Abuse and Addiction for the Oncology Setting
An appropriate definition of addiction would take into account that it is a chronic disorder characterized by “the compulsive use of a substance resulting in physical, psychological, or social harm to the user and continued use despite that harm.”[22] While not without problems, this definition appropriately stresses that addiction is, fundamentally, a psychological and behavioral syndrome.

Even such an appropriate definition will have limited utility unless specifically applied to the clinical oncology setting. We have found that the concept of “aberrant drug-related behavior” is a useful heuristic in operationalizing the definitions of abuse and addiction, since it comprises a broad range of behaviors that may be considered problematic by oncologists prescribing medications for pain and symptom management (Table 2). The occurrence of aberrant behaviors signals the need to reevaluate and manage drug-taking.

Differential Diagnosis

If problematic drug-taking behavior appears during pain treatment, a “differential diagnosis” for this behavior should be considered (Table 3). A true addiction (substance dependence) is only one of several possible etiologies. Pseudoaddiction must be considered if the patient is reporting distress associated with unrelieved symptoms—even if the aberrant behaviors themselves are dramatic or worrisome.

Alternatively, impulsive drug use may indicate the existence of another psychiatric disorder, the diagnosis and treatment of which may have therapeutic implications. Psychiatric assessment is critically important both in the population without a prior history of substance abuse and the population of known abusers, who have a high prevalence of psychiatric comorbidity.[23]

Some patients may be self-medicating symptoms of anxiety or depression, insomnia, or even problems of adjustment (such as boredom due to diminished ability to engage in usual activities and hobbies). Others have character pathology that may be the more salient determinant of drug-taking behavior. For example, patients with borderline personality disorder may use prescribed drugs in a chaotic, impulsive manner that regulates inner tension; expresses anger at doctors, friends, or family; or ameliorates chronic emptiness or boredom.

From time to time, aberrant drug-related behavior appears to be causally related to a mild encephalopathy, with confusion about the appropriate therapeutic regimen. On rare occasions, problematic behaviors indicate criminal intent (ie, intent to sell or divert). These diagnoses are not mutually exclusive.

In assessing the differential diagnosis for drug-related behavior, it is also useful to consider the degree of aberrance of a given behavior (Table 2), recognizing that they exist along a spectrum. The less aberrant behaviors (such as aggressively complaining about the need for medications) are more likely to reflect untreated distress of some type, rather than addiction-related concerns. Conversely, the more aberrant behaviors (such as injection of an oral formulation) are more likely to reflect true addiction. Although empiric studies are needed to validate this conceptualization, it may be a useful model when evaluating aberrant behaviors.

Reviews of this article will appear in next month's issue.

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