A compound selected from the group consisting of 2-(1-hydroxyethyl)-naphtho[2,3-b]furan-4,9-dione, 2-acetyl-7-chloro- naphtho[2,3-b]furan-4,9-dione, 2-acetyl-7-fluoronaphtho[2,3-b]furan-4,9-dione, 2- acetylnaphtho[2,3-b]furan-4,9-dione, 2-ethylnaphtho[2,3-b]furan-4,9-dione, phosphoric acid mono-[1-(4,9-dioxo-4,9-dihydronaphtho[2,3-b]furan-2-yl)-vinyl]ester, phosphoric acid 1-(4,9-dioxo-4,9-dihydronaphtho[2,3-b]furan-2-yl)-vinyl ester dimethyl ester, and a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition comprising said compound, for use in: (i) a method of treating a subject, the method comprising the steps of identifying a subject by aberrant Stat3 pathway activity and administering to the subject a therapeutically effective amount of the compound; (ii) an in vivo method of inhibiting a cancer stem cell to treat cancer in a subject, the method comprising administering to a cancer stem cell an effective amount of the compound; (iii) a method of treating a subject for cancer refractory to a chemotherapy and/or radiotherapy, the method comprising administering to the subject a therapeutically effective amount of the pharmaceutical composition; (iv) a method of treating or preventing cancer relapse in a subject, the method comprising administering to the subject a therapeutically effective amount of the pharmaceutical composition; (v) a method of treating or preventing cancer metastasis in a subject, the method comprising administering to the subject a therapeutically effective amount of the pharmaceutical composition; (vi) a method of inhibiting a cancer stem cell to treat cancer in a subject, wherein the method selectively targets cancer cells in a subject, the method comprising administering to a subject a pharmaceutical composition, such that the compound concentration in the subject's plasma is not maintained above a critical concentration for more than 24 hours after each dose, thereby selectively killing cancer cells while substantially sparing normal cells; (vii) a method of inhibiting a cancer stem cell to treat cancer in a subject, the method comprising administering to the subject a therapeutically effective amount of the pharmaceutical composition. (i) a method of treating a subject, the method comprising the steps of identifying a subject by aberrant Stat3 pathway activity and administering to the subject a therapeutically effective amount of the compound; (ii) an in vivo method of inhibiting a cancer stem cell to treat cancer in a subject, the method comprising administering to a cancer stem cell an effective amount of the compound; (iii) a method of treating a subject for cancer refractory to a chemotherapy and/or radiotherapy, the method comprising administering to the subject a therapeutically effective amount of the pharmaceutical composition; (iv) a method of treating or preventing cancer relapse in a subject, the method comprising administering to the subject a therapeutically effective amount of the pharmaceutical composition; (v) a method of treating or preventing cancer metastasis in a subject, the method comprising administering to the subject a therapeutically effective amount of the pharmaceutical composition; (vi) a method of inhibiting a cancer stem cell to treat cancer in a subject, wherein the method selectively targets cancer cells in a subject, the method comprising administering to a subject a pharmaceutical composition, such that the compound concentration in the subject's plasma is not maintained above a critical concentration for more than 24 hours after each dose, thereby selectively killing cancer cells while substantially sparing normal cells; (vii) a method of inhibiting a cancer stem cell to treat cancer in a subject, the method comprising administering to the subject a therapeutically effective amount of the pharmaceutical composition.