Spontaneous regression or remission (SR) of cancers has been defined as the disappearance of the malignancies without any treatment or with obviously inadequate treatment. Four case reports are presented. These include a case of pleomorphic liposarcoma with bilateral lung metastases, a case of recurrent squamous cell carcinoma of the esophagus following esophagectomy a year earlier, a case of a squamous cell carcinoma of the scalp, and a case of a ruptured hepatocellular carcinoma with an emergency right hepatic lobectomy but with some gross cancer remaining in the left hepatic lobe. The literature of SR of cancers was reviewed and various mechanisms possibly involved in the disappearance of the cancers were discussed. Although immune modulation has been stated to be the most likely process causing SR, other mechanisms, such as genetic therapy, withdrawal of carcinogens, infection, fever and vaccine roles, apoptosis, antibody, antiangiogenesis and maturation mechanisms, withdrawal of therapy, natural killer activity, endocrine, hormonal, and pregnancy factors, and prayers or psychoneuro-religious participation were also mentioned. Induction and inhibition of malignant protein expression and repair of gene damage may prove to be the more important processes in cancer regression. It was also pointed out that the pulmonary metastases of the liposarcoma and the recurrent squamous cell carcinoma of the esophagus may be the very first cases of their kind to be described and that it is rare indeed to find 4 cases of SR's in a solo practice. Finally, it is likely that SR is rarer than previously believed and that the incidence may be one in every 140,000 cases of cancer rather the one per 60,000 to 100,000 cancer cases as earlier thought.