Drugs, in particular, anticancer agents. More particularly speaking, anticancer agents which contain as the active ingredient(s) one or more compounds selected from among omega -hydroxyfatty acids having a specific chemical structural formula and salts and esters thereof, hydroxyoxofatty acids and salts and esters thereof, lactone compounds, macrocyclic ketones and macrocyclic diesters. The above-described compounds have a carcinostatic effect, an extremely high effect of preventing cancer metastasis, an effect of preventing recurrence of cancer, an effect of preventing the occurrence of cancer and little cytotoxicity. Moreover, these compounds are efficacious only in a small dose. Owing to these characteristics, these compounds enable the provision of anticancer agents with little side effect. The effect of preventing cancer metastasis can be further enhanced by the combined use with known anti-malignant tumor agents. Among the anticancer agents as described above, omega -hydroxyfatty acids can be very conveniently obtained at a high purity by hydrolyzing lactone compounds which are also the anticancer agents as described herein.