The immune system plays a pivotal role against cancer. The development of a successful immune response involves the balance between the Th1 (antitumor) and Th2 (protumor) responses. Once this balance is lost, diseases such as cancer may become apparent. Surgical stress, volatile anaesthetics, opioids and blood transfusions are known to favour a Th2 response that manifests as immune suppression. During surgery the load of circulating malignant cancer cells is increased by tumour manipulation. These cancer cells can migrate and seed in distant tissues and form metastasis. Also, some cancer patients may present with micrometastasis that may become invasive if left untreated. Therefore, the perioperative period is a moment of immunological vulnerability in cancer patients. A better understanding of the factors that affect the Th1/Th2 balance may allow anaesthesiologists to identify patients at high risk for cancer recurrence. This review describes the perioperative interventions that can alter the Th1/Th2 balance, during the perioperative period of oncological surgery.