The report is prepared for the general information of shareholders. It is authorized for distribution to prospective investors only when preceded or accompanied by a current prospectus.

LETTER FROM THE EXECUTIVE CHAIR

Dear Shareholders:

Markets experienced dramatic swings in early 2020 as the coronavirus pandemic brought the global economy to a standstill for several months. Optimism over the

development of vaccines and therapeutics, along with a decline in cases in countries affected by the outbreak early on, brightened the economic and market outlook, as did the phased reopening of U.S. states. However, significant uncertainty remains. While policymakers and public health officials have learned a great deal about combating the virus, much remains unknown at a time when another wave of infections is underway. In the United States, political uncertainty eased after former Vice President Joe Biden was projected as the winner of the presidential election. Since the pandemic caused many jurisdictions to adopt mail-in voting for the first time, the counting of ballots has been slower than normal this cycle. Republicans appear likely to retain control of the Senate, though whether they do will not be known until a

pair of early January runoff elections takes place in Georgia.

Global central banks have taken aggressive steps to cushion the economic and market fallout related to the virus, and governments are deploying unprecedented levels of fiscal support, though in the U.S. some of those measures were allowed to lapse at the end of July as negotiators found themselves at an impasse over the scope of additional funding. The measures already put in place have helped build a supportive environment and are encouraging economic recovery; however, if markets disconnect from fundamentals, they can also sow the seeds of instability. In the aftermath of the crisis, societal changes may be likely, as households, businesses, and governments adjust to a new reality, and any such alterations could affect the investment landscape. For investors, events such as the COVID-19 outbreak demonstrate the importance of having a deep understanding of company fundamentals, and we have built our global research platform to do just that.

Here at MFS®, we aim to help our clients navigate the growing complexity of the markets and world economies. Our long-term investment philosophy and commitment to the responsible allocation of capital allow us to tune out the noise and uncover what we believe are the best, most durable investment opportunities in the market. Through our unique global investment platform, we combine collective expertise, thoughtful risk management, and long-term discipline to create sustainable value for investors.

Respectfully,

Robert J. Manning

Executive Chair

MFS Investment Management

November 13, 2020

The opinions expressed in this letter are subject to change and may not be relied upon for investment advice. No forecasts can be guaranteed.

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PORTFOLIO COMPOSITION

Cash & Cash Equivalents includes any cash, investments in money market funds, short-term securities, and other assets less liabilities. Please see the Statement of Assets and Liabilities for additional information related to the fund’s cash position and other assets and liabilities.

Percentages are based on net assets as of September 30, 2020.

The portfolio is actively managed and current holdings may be different.

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MANAGEMENT REVIEW

Summary of Results

For the twelve months ended September 30, 2020, Class A shares of the MFS Blended Research Core Equity Fund (fund) provided a total return of 12.88%, at net asset value. This compares with a return of 15.15% for the fund’s benchmark, the Standard & Poor’s 500 Stock Index (S&P 500 Index).

Market Environment

Markets experienced an extraordinarily sharp selloff and, in many cases, an unusually rapid recovery late in the period. Central banks and fiscal authorities undertook astonishing levels of stimulus to offset the economic effects of government-imposed social-distancing measures implemented to slow the spread of the COVID-19 virus. At this point, the global economy looks to have experienced the deepest, steepest and possibly shortest recession in the postwar period. However, the recovery remains subject to more than the usual number of uncertainties due to questions about the evolution of the virus, what its continued impact will be and when vaccines or medicines will become available to prevent or treat it.

Around the world, central banks responded quickly and massively to the crisis with programs to improve liquidity and support markets. These programs proved largely successful in helping to restore market function, ease volatility and stimulate a continued market rebound. Late in the period, the US Federal Reserve adopted a new, flexible average-inflation-targeting framework, which is expected to result in policy rates remaining at low levels for a longer period. In developed countries, monetary easing measures were complemented by large fiscal stimulus initiatives, although late in the period there was uncertainty surrounding the timing and scope of additional US recovery funding. Due to relatively manageable external liabilities and balances of payments in many countries, along with persistently low inflation, even emerging market countries were able to implement countercyclical policies – a departure from the usual market-dictated response to risk-off crises.

Compounding market uncertainty earlier in the pandemic was a crash in the price of crude oil due to a sharp drop in global demand and a disagreement between Saudi Arabia and Russia over production cuts, which resulted in a price war. The subsequent decline in prices undercut oil exporters, many of which are in emerging markets, as well as a large segment of the high-yield credit market. The OPEC+ group later agreed on output cuts, with shale oil producers in the United States also decreasing production, which, along with the gradual reopening of some major economies and the resultant boost in demand, helped stabilize the price of crude oil.

As has often been the case in a crisis, market vulnerabilities have been revealed. For example, companies that have added significant leverage to their balance sheets in recent years by borrowing to fund dividend payments and stock buybacks have, in many cases, halted share repurchases and cut dividends, while some firms have been forced to recapitalize.

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Management Review – continued

Detractors from Performance

Although stock selection in the health care sector was a primary detractor from performance relative to the S&P 500 Index, there were no individual stocks within this sector that were among the fund’s largest relative detractors during the reporting period.

Security selection and, to a lesser extent, an overweight position in the utilities sector also held back relative results, led by the fund’s overweight position in energy infrastructure company Sempra Energy. The share price of Sempra Energy declined at the beginning of the calendar year amidst global demand concerns, given broad-based macroeconomic uncertainty. Also, the company reduced its production outlook for its Liquid Natural Gas (LNG) project development at Port Arthur, which further pressured the share price.

Stock selection in both the financials and consumer staples sectors weakened relative returns. Within the financials sector, overweight positions in diversified financial services firm Citigroup, consumer financial services firm Synchrony Financial ^(h), insurance company MetLife and financial services firm Bank of America dampened relative results. The share price of many banks, including Citigroup, declined over increased loan losses due to a dramatic slowdown in global economic activity as countries took measures to stop the spread of the coronavirus. Within the consumer staples sector, an overweight position in brewery company Molson Coors Brewing held back relative returns as the company’s total sales volumes fell short of expectations, driven by weaker-than-anticipated performance across both North America and Europe. The company’s temporary keg relief programs, which provided customers with reimbursements for untapped kegs that met certain established return requirements, further pressured its earnings and share price.

Stocks in other sectors that detracted from relative returns included overweight positions in independent oil refiner Valero Energy and energy exploration and production company EOG Resources. The share price of Valero fell over concerns about global refining fundamentals and its negative impact on margins, given capacity additions, unfavorable crude differentials and lower refining utilization rates. Holdings of real estate investment trust STORE Capital ^(b), and the timing of the fund’s ownership in shares of computer graphics processors maker NVIDIA, also weighed on relative performance.

Contributors to Performance

During the reporting period, stock selection and, to a lesser extent, an underweight position in the industrials sector contributed to relative performance. Within this sector, not owning shares of aerospace company Boeing boosted relative results. The share price of Boeing declined as the travel and airline industries came under intense pressure amid the outbreak of the COVID-19 virus, which resulted in widespread travel restrictions across the globe and ultimately led the company to suspend production.

Security selection and, to a lesser extent, an underweight position in the consumer discretionary sector also boosted relative results. There were no individual stocks within this sector that were among the fund’s largest relative contributors during the period.

Stock selection in the communication services sector supported relative returns. Within this sector, an underweight position in telecommunication services provider AT&T ^(h),

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Management Review – continued

and an overweight position in cable services provider Charter Communications, benefited relative returns. The share price of AT&T traded lower during the period, as the company reported weaker-than-expected earnings, owing to lower cable-network advertising revenue and foreign exchange headwinds, paired with uncertainty stirred by COVID-19 market disruptions.

Individual stocks in other sectors that helped relative performance included the fund’s overweight positions in computer and personal electronics maker Apple, software giant Microsoft, pharmaceutical company Eli Lilly and broadcast and communication tower management firm American Tower ^(h). Despite headwinds related to the pandemic, the share price of Apple appreciated steadily during the period. The company’s product demand was stronger than expected, driven by higher online sales and service revenue, combined with an all-time record in revenue from its App Store. Additionally, the shift toward work-from-home and remote learning helped to support strong iPhone and iPad sales. Underweight positions in integrated oil and gas company Exxon Mobil ^(h), diversified financial services firm Wells Fargo ^(h) and integrated energy company Chevron ^(h) also contributed to relative performance. The share price of Exxon Mobil suffered during the period as oil and gas prices came under significant pressure due to lower demand caused by COVID-19 disruptions and the price war between Saudi Arabia and Russia. Disappointing chemical and refining margins, as well as higher costs, also affected its share price.

Respectfully,

Portfolio Manager(s)

Jim Fallon, Matt Krummell, Jonathan Sage, and Jed Stocks

The views expressed in this report are those of the portfolio manager(s) only through the end of the period of the report as stated on the cover and do not necessarily reflect the views of MFS or any other person in the MFS organization. These views are subject to change at any time based on market or other conditions, and MFS disclaims any responsibility to update such views. These views may not be relied upon as investment advice or an indication of trading intent on behalf of any MFS portfolio. References to specific securities are not recommendations of such securities, and may not be representative of any MFS portfolio’s current or future investments.

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PERFORMANCE SUMMARY THROUGH 9/30/20

The following chart illustrates a representative class of the fund’s historical performance in comparison to its benchmark(s). Performance results include the deduction of the maximum applicable sales charge and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. The performance of other share classes will be greater than or less than that of the class depicted below. Benchmarks are unmanaged and may not be invested in directly. Benchmark returns do not reflect sales charges, commissions or expenses. (See Notes to Performance Summary.)

Performance data shown represents past performance and is no guarantee of future results. Investment return and principal value fluctuate so your shares, when sold, may be worth more or less than the original cost; current performance may be lower or higher than quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on fund distributions or the redemption of fund shares.

Growth of a Hypothetical $10,000 Investment

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Performance Summary – continued

Total Returns through 9/30/20

Average annual without sales charge

Benchmark Definition(s)

Standard & Poor’s 500 Stock Index – a market capitalization-weighted index of 500 widely held equity securities, designed to measure broad U.S. equity performance. “Standard & Poor’s®” and “S&P®” are registered trademarks of Standard & Poor’s Financial Services LLC (“S&P”) and Dow Jones is a registered trademark of Dow Jones Trademark Holdings LLC (“Dow Jones”) and have been licensed for use by S&P Dow Jones Indices LLC and sublicensed for certain purposes by MFS. The S&P 500® is a product of S&P Dow Jones Indices LLC, and has been licensed for use by MFS. MFS’s product(s) is not sponsored, endorsed, sold, or promoted by S&P Dow Jones Indices LLC, Dow Jones, S&P, or their respective affiliates, and neither S&P Dow Jones Indices LLC, Dow Jones, S&P, nor their respective affiliates make any representation regarding the advisability of investing in such product(s).

It is not possible to invest directly in an index.

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Performance Summary – continued

Notes to Performance Summary

Average annual total return represents the average annual change in value for each share class for the periods presented. Life returns are presented where the share class has less than 10 years of performance history and represent the average annual total return from the class inception date to the stated period end date. As the fund’s share classes may have different inception dates, the life returns may represent different time periods and may not be comparable. As a result, no comparative benchmark performance information is provided for life periods.

Performance results reflect any applicable expense subsidies and waivers in effect during the periods shown. Without such subsidies and waivers the fund’s performance results would be less favorable. Please see the prospectus and financial statements for complete details.

Performance results do not include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles and may differ from amounts reported in the financial highlights.

From time to time the fund may receive proceeds from litigation settlements, without which performance would be lower.

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EXPENSE TABLE

Fund expenses borne by the shareholders during the period,

April 1, 2020 through September 30, 2020

As a shareholder of the fund, you incur two types of costs: (1) transaction costs, including sales charges (loads) on certain purchase or redemption payments, and (2) ongoing costs, including management fees; distribution and service (12b-1) fees; and other fund expenses. This example is intended to help you understand your ongoing costs (in dollars) of investing in the fund and to compare these costs with the ongoing costs of investing in other mutual funds.

The example is based on an investment of $1,000 invested at the beginning of the period and held for the entire period April 1, 2020 through September 30, 2020.

Actual Expenses

The first line for each share class in the following table provides information about actual account values and actual expenses. You may use the information in this line, together with the amount you invested, to estimate the expenses that you paid over the period. Simply divide your account value by $1,000 (for example, an $8,600 account value divided by $1,000 = 8.6), then multiply the result by the number in the first line under the heading entitled “Expenses Paid During Period” to estimate the expenses you paid on your account during this period.

Hypothetical Example for Comparison Purposes

The second line for each share class in the following table provides information about hypothetical account values and hypothetical expenses based on the fund’s actual expense ratio and an assumed rate of return of 5% per year before expenses, which is not the fund’s actual return. The hypothetical account values and expenses may not be used to estimate the actual ending account balance or expenses you paid for the period. You may use this information to compare the ongoing costs of investing in the fund and other funds. To do so, compare this 5% hypothetical example with the 5% hypothetical examples that appear in the shareholder reports of the other funds.

Please note that the expenses shown in the table are meant to highlight your ongoing costs only and do not reflect any transactional costs, such as sales charges (loads). Therefore, the second line for each share class in the table is useful in comparing ongoing costs only, and will not help you determine the relative total costs of owning different funds. In addition, if these transactional costs were included, your costs would have been higher.

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Expense Table – continued

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Portfolio of Investments – continued

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Portfolio of Investments – continued

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Portfolio of Investments – continued

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Portfolio of Investments – continued

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Portfolio of Investments – continued

The following abbreviations are used in this report and are defined:

See Notes to Financial Statements

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Financial Statements

STATEMENT OF ASSETS AND LIABILITIES

At 9/30/20

This statement represents your fund’s balance sheet, which details the assets and liabilities comprising the total value of the fund.