The term “sickness behavior” refers to a series of behavioral and physiological changes that occur after exposure to an inflammatory or infectious agent, or after administration of recombinant proinflammatory cytokines. Symptoms of sickness behavior include social withdrawal, anhedonia, cognitive impairment, anorexia, fever, and other symptoms. Behavioral changes associated with sickness behavior are transient in nature and serve adaptive purposes that help the individual mount an effective immune response.

Considerable attention has focused on the role of centrally acting cytokines in mediating sickness behavior. As might be expected, abnormal increases in cytokines appear to result in psychopathological outcomes. Indeed, sickness behavior and clinical depression (among other psychiatric disturbances) are evident in patients receiving cytokine therapy. Increased proinflammatory cytokine activity has been implicated in the etiology of depression, schizophrenia, and other psychiatric disorders.

Cancer-related symptoms are strikingly similar to the symptoms associated with cytokine-induced sickness behavior. On the basis of this observation and coupled with evidence that behavioral disturbances in patients with cancer may occur coincident with abnormal increases in proinflammatory cytokines, it has been suggested that common cytokine-related signaling pathways underlie sickness-related and cancer-related symptoms. In this chapter, we will discuss similarities between cancer-related symptoms and sickness behavior, and we will examine potential common mediators and mechanisms, including proinflammatory cytokines and subsequent interactions with neurotransmitter and molecular signaling pathways.

Cancer-related symptoms

Cancer-related symptoms refer to physical and psychiatric manifestations produced by the disease process or treatment (including chemotherapy, radiotherapy, immunotherapy, and surgical procedures). Cancer-related symptoms may be categorized as physical, cognitive, or affective.