Strategy. MFS (Massachusetts Financial Services Company, the fund's investment adviser) seeks to achieve the fund's objective by actively identifying potential investments based on fundamental and quantitative analysis and then constructing a portfolio from these potential investments while managing various risk factors (e.g., issuer, industry, and sector weightings, market capitalization, and volatility ) compared to the Russell Midcap Index, which represents the fund's investment universe. MFS normally invests at least 80% of the funds net assets in equity securities of issuers with medium market capitalizations. MFS generally defines medium market capitalization issuers as issuers with market capitalizations similar to those of issuers included in the Russell Midcap Index over the last 13 months at the time of purchase. As of August 31, … Show more… MFS (Massachusetts Financial Services Company, the fund's investment adviser) seeks to achieve the fund's objective by actively identifying potential investments based on fundamental and quantitative analysis and then constructing a portfolio from these potential investments while managing various risk factors (e.g., issuer, industry, and sector weightings, market capitalization, and volatility ) compared to the Russell Midcap Index, which represents the fund's investment universe. MFS normally invests at least 80% of the funds net assets in equity securities of issuers with medium market capitalizations. MFS generally defines medium market capitalization issuers as issuers with market capitalizations similar to those of issuers included in the Russell Midcap Index over the last 13 months at the time of purchase. As of August 31, 2025, the range of the market capitalizations of the issuers in the Russell Midcap Index was between approximately $1.1 billion and $98.7 billion. Equity securities include common stocks, depositary receipts, equity interests in real estate investment trusts (REITs), and other securities that represent an ownership interest (or right to acquire an ownership interest) in a company or other issuer. In selecting investments for the fund, MFS is not constrained by any particular investment style. MFS may invest the funds assets in the stocks of companies it believes to have above average earnings growth potential compared to other companies (growth companies), in the stocks of companies it believes are undervalued compared to their perceived worth (value companies), or in a combination of growth and value companies. MFS may invest the funds assets in foreign 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. MFS uses an active bottom-up approach to buying and selling investments for the fund. Investments are selected primarily based on blending fundamental and quantitative research. MFS uses fundamental analysis of individual issuers to determine a fundamental rating for an issuer. MFS uses quantitative analysis to determine a quantitative rating for an issuer. MFS combines the fundamental rating with the quantitative rating to create a blended rating for an issuer. When the fundamental rating is not available, MFS treats the issuer as having a neutral fundamental rating. MFS constructs the portfolio using a portfolio optimization process that considers the blended rating, as well as issuer, industry, and sector weightings, market capitalization, volatility, and other factors. The portfolio managers have the discretion to adjust the inputs and parameters used in the optimization process and the fund's portfolio holdings based on factors such as the desired portfolio characteristics and the portfolio managers qualitative assessment of the optimization results. MFS' goal is to construct an actively managed portfolio with a target predicted tracking error of approximately 3% compared to the Russell Midcap Index. Tracking error generally measures how the differences between the fund's returns and the Russell Midcap Index's returns have varied over a period of time. For purposes of the fund's 80% policy, net assets include the amount of any borrowings for investment purposes. Show less