It has now been shown that overweight and obesity are associated with the development of at least 13 types of cancer, including cancer of the breast, colon and rectum, endometrium, esophagus (adenocarcinoma), gallbladder, stomach, kidney (renal cell), liver, ovaries, pancreas and thyroid glands, as well as multiple myeloma. Obesity-related cancers account for about 40% of all cancers. Thus, obesity is ahead of smoking as the most common modifiable risk factor for carcinogenesis. This review collects the latest data on the impact of obesity phenotypes on the risk of developing cancer, including a discussion of the contribution of the metabolically healthy obesity phenotype (MHO) to tumorigenesis. Possible mechanisms contributing to the emergence and progression of cancer are analyzed, for example: stimulation of cell proliferation, evasion of growth suppressors, inhibition of apoptosis and provision of replicative immortality, induction of angiogenesis, activation of invasion and metastasis, influence on genome instability, as well as chronic low-grade inflammation that contributes to the development of cancer. Understanding how obesity influences the above mechanisms may facilitate the development of new cancer prevention and treatment strategies for obese populations.