Evidence from epidemiological studies suggests that diets rich in n-3 PUFA may be associated with reduced cancer risk. These observations have formed the rationale for exploring the mechanisms by which n-3 PUFA may be chemoprotective and have resulted in significant advances in our mechanistic understanding of n-3 PUFA action on tumour growth. Various interrelated and integrated mechanisms may be at work by which n-3 PUFA influence cancer at all stages of initiation, promotion, progression, and neoplastic transformation. More recently, experimental studies have reported enhanced tumour cell death with chemotherapy when fish oil is provided while toxic side effects to the host are reduced. Furthermore, cancer-associated wasting has been shown to be attenuated by fish oil supplementation. Clinical evidence suggests that the n-3 PUFA status of newly diagnosed cancer patients and individuals undergoing chemotherapy is low. Therefore, both the disease itself and therapeutic treatments may be contributing factors in the decline of n-3 PUFA status. Dietary supplementation to maintain and replenish n-3 PUFA status at key points in the cancer disease trajectory may provide additional health benefits and an enhanced quality of life. The present review will focus on and critically examine current research efforts related to the putative anti-cancer effects of n-3 PUFA and their suggested ability to palliate cancer-associated and treatment-associated symptoms.