Swiss drugmaker Roche Holding AG (ROG.VX) said Wednesday that it decided not to extend beyond Friday a $6.8 billion hostile offer for gene sequencing specialist Illumina Inc. (Nasdaq: ILMN) after determining that the incumbent directors of Illumina will be re-elected.

We do not believe that a price above Roche's offer for Illumina of $51 per share would be in the interest of Roche's shareholders, Roche Chief Executive Severin Schwan said in a statement.

Roche, the world's biggest maker of cancer drugs, is targeting to expand the market share of its diagnostic products by taking over Illumina. Roche started an offer to acquire the San Diego company's shares for $44.50 each in January. It then raised that to $51 last month.

Roche's offer values the gene-sequencing company at about 88 percent above its closing share price on Dec. 21, when rumors about a potential bid first surfaced. The offer expires Friday at 6 p.m. New York time, Roche said.

Illumina, which has branded itself the Apple of the genomics business, has rejected Roche's sweetened takeover offer and had repeatedly urged shareholders to vote against Roche's nominees to its board.

Illumina believes the offer is undervaluing its extraordinary growth prospects, while Roche has called its bid full, fair and extremely attractive.

Roche had moved to force Illumina into negotiations by starting a proxy fight to gain control of the San Diego-based company's board, but failed when shareholders backed all four of Illumina's nominees to the board, based on preliminary estimates at the company's annual meeting in New York. Illumina shareholders also rejected Roche's attempt to expand Illumina's board to 11 from nine members.

In view of the apparent results, Roche announced it is officially walking away on its own terms.

Roche will continue to consider options and opportunities to develop further its portfolio of businesses in order to expand its diagnostics leadership position, CEO Severin Schwan said.

Ilumina shares fell as much as 8.3 percent in Wednesday's morning trading, before closing up 1.16 percent, to $44.51 a share, while Roche gained 0.93 percent to $44.47.