The fund seeks to meet its objective by investing, under normal circumstances, at least 80% of its assets (net assets plus the amount of any borrowings made for investment purposes) in issuers with medium market capitalizations. MFS normally invests the fund's assets primarily in equity securities. MFS normally invests the fund's assets across different industries and sectors, but MFS may invest a significant percentage of the fund's assets in issuers in a single industry or sector.