Shares of Express Scripts (ESRX)  closed lower by 10.77% to $60.01 on heavy trading volume Tuesday, after the pharmacy benefit manager said it is likely to lose its biggest customer, Anthem (ANTM - Get Report) .

Anthem had sued Express Scripts in the past, claiming it had been over charged. Now Express is saying it is not likely Anthem will renew its contract once it ends in 2019.

"Although conversations have been ongoing, the company was recently told by Anthem management that Anthem intends to move its business when the company's current contract with Anthem expires on December 31, 2019, and that Anthem is not interested in continuing discussions regarding pricing concessions for 2017-2019 or in receiving the company's proposed pricing for the period beyond 2019" Express said.

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This story was update from its original publish time of 10:56 a.m.