Calling the program overly stringent, four Pioneer accountable care organizations are ending their experimental venture into the higher risk and reward payment agreement with Medicare. They join the nine ACOs that exited the program last year.

Four pioneer ACOs—Genesys PHO of Flint, Mich., Franciscan Alliance of central Indiana, Renaissance Health Network of Pennsylvania and Sharp Healthcare of San Diego—are throwing in the towel, reports the Wall Street Journal.

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