Both Roche and Illumina sent letters to Illumina shareholders a month ahead of the company’s annual meeting on April 18 urging them to vote for their board of directors’ nominations. Roche, in January, made a $5.7 billion hostile takeover bid for Illumina, which Illumina’s current board of directors has rejected as grossly undervaluing the company.

“Roche Holding Ltd—an Illumina competitor with a track record of pursuing hostile acquisitions—is trying to buy Illumina at a low-ball price and capture our future growth and value potential for its own stockholders,” wrote Jay Flatley, Illumina’s president and CEO, and William Rastetter, its chairman. They warned Illumina shareholders that supporting Roche’s board nominees would “steal value that rightly belongs to you.”

Roche fired back quickly, sending its own letter to shareholders urging them to support its board nominees. “We believe that our offer is full and fair and provides value certainty and liquidity to shareholders amid increasing headwinds for Illumina and the broader sequencing sector,” wrote Severin Schwan, CEO of Roche Group. He warned that Illumina’s growth prospects had diminished in the past year and were likely to continue to be impacted “as the gene sequencing market continues to mature and prices decline.” Schwan said going forward, Illumina would have to invest heavily to expand its market share in an increasingly competitive global market.

Roche first made its intentions clear on January 26. Illumina’s board immediately adopted a “poison pill” strategy that would take effect should any one entity acquire 15 percent of the company’s shares. Still, on January 27 Roche commenced a hostile tender offer to acquire all the outstanding shares of Illumina for $44.50 a share, which, when the offer was announced, represented an 18 percent premium to its trading price of $37.68 a share. Illumina’s shares traded as high as $79.40 in July 2011 before market volatility took its toll and sent shares as low as $25.57 in mid-October.

Illumina is one of the top players in genomics and DNA sequencing technology. The takeover attempt is seen as an effort by Roche to create a personalized medicine powerhouse, with both genomic sequencing and targeted therapeutics capabilities.

Roche’s tender offer expires on March 26, 2012 but will likely be extended and both companies will continue their campaign to win shareholders to their side. Roche has stood firm on the price it is willing to pay for Illumina, but this could change if it is unsuccessful in getting its board nominees elected.

Roche has shown patience and perseverance in its last two big takeover attempts, which were ultimately completed. It fought to acquire Ventana Medical Systems for seven months before succeeding to acquire it at a 19 percent premium; and it took close to eight months before it sealed the deal to acquire the 44.1 percent of Genentech it did not already own for $46.8 billion. In that deal it had to raise its offer to $95 per share, $6 a share more than the original offer of $89 per share.