Separately, in a sign of the industry's rapid consolidation, The Wall Street Journal reported that Aetna was making a takeover proposal to Humana—a key player in Medicare. The paper reported last month that the company has been approached by both Aetna and Humana.
Anthem has now made four separate offers for its competitor, but Cigna has rebuffed the company's entreaties. As other health care companies strike deals, Anthem hiked its offer to a proposed premium of 35.4 percent of Cigna's closing price on May 28.
In its latest offer, Anthem indicated that its willingness to strike a deal was running out, calling Cigna's demands "unreasonable."
"Anthem expresses frustration with and urges Cigna's board of directors to drop unreasonable governance demands in light of the significant premium being offered and return to negotiations to reach a mutually agreed upon transaction," Anthem said in a statement.
Aetna closed the session Friday at $124.07, while Humana was up about $3 over $202. Cigna finished the session down $1.11 at $155, and Anthem down marginally at $165.06.