Work with low-molecular-weight heparins (LMWHs) continues to provide suggestions for survival advantages among patients with cancer diagnoses. Momentum is building in support of this theory through reports, the vast majority of which are derived from secondary analyses of clinical trials on the treatment of thromboembolism. The data retrieved from such studies that compare unfractionated heparin (UFH) with LMWH indicate that LMWH is equally beneficial if not more beneficial to cancer patients in terms of survival. In retrospective analysis, this improved life expectancy is not considered a result of reduced complications from thromboembolism. Thus, theories of antitumor effects of LMWH have developed, supported by evidence that most of the survival benefits are during long-term comparisons. Reports describing the effects of heparin in the setting of cancer have existed for over a half-century, although specific mechanisms for the marginal results seen thus far have yet to surface. Proposals for the most likely targets of the effective heparins include enzyme interaction, cellular growth modifications, and antiangiogenesis.