AstraZeneca (AZN -0.44%) played hard to get and won, at least for now. The British pharmaceutical major this month rejected two nine-figure buyout offers from Pfizer (PFE -0.30%), which now must wait at least three months before making any additional offers.

While it's never fun to be spurned, Pfizer investors may ultimately be better off with the deal that never happened, especially if the company shifts its attention to other targets, such as oncology and autoimmune giant Celgene (CELG).

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Shifting attention to other oncology leaders
AstraZeneca's appeal stems in large part from its current and future oncology drugs. The company already markets cancer therapies accounting for more than $700 million in quarterly sales, and it has a host of promising oncology treatments in its pipeline, including Olaparib, an ovarian cancer drug under consideration by U.S. and European regulators.

Those products would fit nicely into Pfizer's oncology line, which includes fast-growing drugs such as Inlyta and Xalkori. Sales of those two drugs respectively grew 40% and 66% in the first quarter, generating a combined total of more than $170 million.

But AstraZeneca is far from the only player in oncology. For example, Celgene and its $62 billion market cap could prove more attractive to Pfizer. 

Celgene's top-selling myeloma drug, Revlimid, generates more than $4 billion in sales per year and, pending some current patent issues being resolved, could offer solid patent protection until at least 2023 or 2024.

Additionally, expansion of Celgene's Abraxane label last fall to include pancreatic cancer has that drug positioned to post sales of nearly $1 billion this year. Celgene also markets Pomalyst, which was approved in 2013 to treat advanced multiple myeloma. Sales of Pomalyst surged 375% year over year to $135 million in the first quarter.

Celgene would also bring its newly approved autoimmune drug, Otezla. Otezla launched in the first quarter as a treatment for psoriatic arthritis, but it could win approval for the far larger psoriasis indication later this year. If so, Otezla could capture a greater share of the market from current blockbusters such as AbbVie's $10 billion-a-year Humira.

Otezla would bolster Pfizer's existing autoimmune drug, Xeljanz, which is approved as a treatment for rheumatoid arthritis. Xeljanz generated sales of $52 million in the first quarter, up from $11 million a year ago.  

Combined, Celgene's product sales totaled $1.7 billion in the quarter, up nearly 20% from a year ago. That has Celgene telling investors to expect full-year sales of $7.5 billion, which would be a 15% increase from 2013.

Fool-worthy final thoughts
Celgene's significant partnership portfolio makes it even more compelling. Celgene has locked up promising collaborations with some of the most intriguing clinical-stage companies, including Epizyme, Agios, and bluebird bio. In addition to collaborating on new therapies with these companies, Celgene has also taken equity interest in some and inked deals that give it the right to acquire companies later on. That pipeline depth could keep Celgene a dominant player through the coming decade.

Granted, Celgene isn't cheap. Its shares trade at roughly 8 times sales. However, that may understate Celgene's true value, as the company projects revenue to double by 2017. If so, growth-seeking companies such as Pfizer may regret it if they don't at least consider trying to buy Celgene now.