Suppression of the immune system is a feature of the post-operative stress response, in which natural killer (NK) and lymphocyte activated killer (LAK) cells form an integral component in immune anti-tumor surveillance. However, a tumor type-specific immune reaction in pancreatic cancer or in patients undergoing surgery is lacking. Anti-tumoral activities of NK and LAK cells are reduced immediately after surgery so the additive effects of surgery may be sufficient to improve the ability of disseminated cancer cells to evade the host immune response long enough for metastases to develop (Da Costa ML, Finnegan N, Flynn M, Bouchier-Hayes DJ. Laparotomy and laparoscopy differentially accelerate experimental flank tumourgrowth. Br J Surg 1998; 85: 1439-42.) (Da Costa ML, Redmond HP, Bouchier-Hayes DJ. The effect of laparotomy and laparoscopy on the establishment of spontaneous tumour metastases. Surgery 1998; 124: 516-26).