The present invention relates to a pharmaceutical composition comprising an HDAC inhibitor, a pharmaceutically acceptable acid or salt thereof or a mixture of the acid and salt, provided both in a immediate release form and in an extended release form wherein 70-90 weight % of the HDAC inhibitor is provided in the immediate release form and the remainder of the HDAC inhibitor is provided in the extended release form. In further aspects the present invention relates to a kit comprising a number of doses of an HDAC inhibitor, a pharmaceutically acceptable acid or salt thereof or a mixture of the acid and salt thereof provided both in an immediate release form and in an extended release form. In still further aspects the present invention relates to an HDAC inhibitor, a pharmaceutically acceptable acid or salt thereof or a mixture of the acid and salt, provided in both an immediate release form and an extended release form, for use in a method of pretreating cancer, and a method of pretreating cancer using said HDAC inhibitor provided both in said immediate release form and said extended release form. Further aspects relate to combination treatment of cancer and to a dispenser for a blister pack.