BOSTON—Steward Health Care System resigned from the Massachusetts Hospital Association, stating that the for-profit system can do more good on its own for the state's hospital industry by transforming into an accountable care organization.

Steward, which owns 10 hospitals in Massachusetts, said in a statement that it will “collaborate as appropriate” with the Massachusetts Hospital Association. “At this point in the evolution of healthcare reform, and of Steward itself, we feel we can make a greater contribution as a single coherent voice with a unique constituency: a fully integrated, community-based accountable care organization,” according to Steward. The Massachusetts Hospital Association said it was “deeply disappointed” with Steward's resignation. The association now has 80 hospital members, the bulk of which are not-for-profit organizations, according to an MHA spokeswoman.

“Our members share a common belief that it is important to participate at a common table for dialogue around healthcare policy and the other important issues in today's healthcare environment,” the association said in a statement. Steward was formed after private-equity firm Cerberus Capital Management acquired Caritas Christi Health Care, a struggling six-hospital Catholic system. “Steward's notice didn't tell us why they resigned, but we doubt it has anything to do with their being investor-owned per se,” MHA President and CEO Lynn Nicholas said in an e-mailed statement. “MHA has a number of long-term hospital members that are investor-owned, including some that are on our Board of Trustees.” At deadline, a spokeswoman for the American Hospital Association was unable to comment on whether Steward's decision could be a sign that other systems may choose to rely on their own influence and sever ties with trade groups. Steward was one of 32 organizations selected recently to participate in the Pioneer ACO Model project through the CMS Innovation Center.