Many factors increase the susceptibility of immunosuppressed cancer patients to infection. Each of these is associated with a unique set of infections, although there is some overlap between predisposing factors and certain infections. Predisposing factors might exist in the same patient, widening the spectrum of potential infections. Recognition of these factors enables the astute clinician to make an accurate prediction of the potential pathogen(s) in a particular patient or setting and to institute appropriate empiric therapy promptly. Table 160-1 lists the predominant defects in host defense mechanisms associated with various cancers and the infections associated with of those defects.