(Reuters) – Bristol-Myers Squibb defended its planned $74 billion takeover of Celgene Corp, saying it had carried out a “robust” assessment of the merger after two major investors opposed what could be the largest pharmaceutical deal ever.

The drugmaker reiterated on Wednesday in a letter to shareholders that buying Celgene was the “best path forward,” even as investors Starboard Value LP and Wellington Management look to thwart the deal.

Starboard, an activist investor with a history of opposing deals it is unhappy with, maintained its view on Wednesday that the merger was “ill-advised” and recommended that fellow Bristol-Myers shareholders vote against it at a meeting slated for April 12.

The New York-based hedge fund has also presented a slate of five nominees to Bristol-Myers’ board, including Starboard Chief Executive Jeffrey Smith.

Wellington, one of Bristol Myers’ top shareholders with a nearly 8 percent stake, has said it finds the deal to be too risky and expensive.

“While (Bristol-Myers’) letter conveys the Board’s belief that the deal is compelling, the intent of the letter also appears to be to address shareholders arguments against the deal,” Credit Suisse analyst Vamil Divan said.

In its appeal to investors, Bristol-Myers highlighted that a buyout of Celgene would provide “significant advantages” with less risk compared with other options like pursuing a series of small transactions.

It also pointed to a six-month “deep-dive analysis” and weeks of confidential due diligence by its advisers that provided a comprehensive view of opportunities and risks associated with buying Celgene.

As its most important cancer immunotherapy Opdivo faces competition from Merck & Co’s Keytruda, Bristol-Myers is betting on Celgene to strengthen its position in the lucrative oncology market.

It also stressed that the deal was expected to increase earnings by over 40 percent in the first full year when it closes.

Meanwhile, a third shareholder, the Loncar Cancer Immunotherapy ETF, also released a statement on Wednesday opposing the deal.

“Celgene’s poor stewardship of recent acquisitions suggests there is more risk in its pipeline than what is being presented at face value,” the fund, which owns $1.65 million worth of Bristol-Myers stock, said.

Bristol-Myers shares were down 1.34 percent at $53.01 in afternoon trading. Celgene’s stock was 0.4 percent lower at $85.91.