The present study sought to evaluate whether altered levels of cytokines may be associated with prospective memory (PM) deficits among breast cancer patients, as examined subjectively and objectively in a longitudinal case-control design, and to investigate possible predictors of these disturbances. As patients often complain of cognitive dysfunction, a secondary aim was to examine whether PM may better account for the self-reported deficits, or if dissociations may be attributable to reduced memory self-awareness. Seventeen women with breast cancer were assessed before chemotherapy and three months post-chemotherapy, and were compared with 17 age- and education-matched healthy controls. Patient PM deficits were found to emerge prior to chemotherapy, and IL-18 may be associated with changes in aspects of PM. Patients did not report more difficulties in PM, and subjective-objective associations were not apparent or explained by memory self-awareness. Interventions to ameliorate PM and associates of systemic inflammation should be investigated.