Health care insurer Cigna Corp. has agreed to a six year extension of its lease in Glendale in a deal with an estimated value of $11.5 million.

The Bloomfield, Conn. firm renewed its 78,000 square foot lease at 400 N. Brand, according to CBRE Group Inc., which announced the transaction Monday.

The extension follows Nestle USA’s decision to renew 400,892 square feet at its 800 North Brand Blvd. headquarters, and the planned relocation next year of Fortune 500 label maker Avery Dennison Corp. from Pasadena to 54,000 square feet at 207 Goode. Ave.

“Glendale’s ability to retain and attract major corporations like Cigna, Avery, and Nestle is critical to the health of the office market there, as well as to local employment,” said R. Todd Doney, vice chairman at the Los Angeles headquarters of CBRE, who represented Cigna and was a broker on the Nestle and Avery Dennison deals.

An industry expert familiar with the deal pegged its value at $11.5 million.

Cigna is the largest tenant in the 177,000 square-foot building and employees about 300 on site, according to real estate data firm CoStar Group Inc. The building is about 80 percent leased.