Psycho-oncology and cancer: psychoneuroimmunology and cancer.

A growing body of research linking psychological and behavioral factors to the incidence and progression of cancer suggests that psychosocial factors may have an impact on some types of cancer [1–6]. In this paper, we suggest that it is through the impact these behavioral and psychological factors have on the cellular immune response, including natural killer (NK) cell function, that they may ultimately affect the occurrence and progression of certain tumors. Our discussion of this link begins with a brief overview of the evidence that psychoneuroimmunology (PNI) research with healthy individuals may be relevant to cancer. Next, to link extant PNI research findings with tumorigenesis, we draw upon two important PNI findings relating psychological distress to two important aspects of carcinogenesis: (i) poorer repair of damaged cellular DNA and (ii) modulation of apoptosis. Finally, we focus on the implications of intervention research in cancer patients for cancer progression and treatment. Before reviewing the evidence regarding stress-related immunological changes, it should be noted that one recurrent concern in the literature is the question of the significance of the immune system for cancer. Cancer is comprised of a heterogeneous group of diseases with multiple etiologies [1], and immunological involvement varies across different cancers. Those cancers that are induced by chemical carcinogens (e.g. lung cancer) may be less influenced by psychological, behavioral and immunological factors than cancers that are associated with a virus, such as Epstein–Barr Virus (EBV), which are immunogenic. Suppression of cellular immunity is associated with a higher incidence of certain types of tumors, particularly EBV-associated lymphoproliferative diseases in organ transplant patients, and Kaposi’s sarcoma and EBVassociated B-cell lymphoma in AIDS patients [7]. Additionally, some researchers have questioned whether stress-related immune changes are of either the type or the magnitude to influence tumor growth and metastases [3, 8]. While such issues are beyond the scope of this paper, compelling evidence exists for the role of cells, such as NK cells, in resisting the progression and metastatic spread of tumors once they have developed [7]. Stress and immune dysregulation