Biotech stocks sport some of the richest valuations in the market today, making it hard to suss out any attractive bargains within this high-flying group. The average forward price-to-earnings ratio among large-cap biotechs, after all, presently stands at a stately 45.2. 

Having said that, blue chip biotechs Amgen (NASDAQ:AMGN) and Celgene Corp. (NASDAQ:CELG) are currently trading at significant discounts relative to their peer group, sporting forward P/E ratios of 12.9 and 13.5, respectively. With these incredibly cheap valuations in mind, let's consider if these two top stocks are worth buying right now.  

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Amgen got lucky, but it's not out of the woods just yet

Amgen's lower-than-average valuation is the result of three key issues. First, the biotech's anti-inflammatory drug Enbrel -- its largest revenue generator -- saw a 15% drop off in sales last year. While management attributed this hefty decline to what they believe will turn out to be a temporary lull in the rheumatology and dermatology markets, there is a worrying alternative explanation.

The arrival of Pfizer's biosimilar to Johnson & Johnson's Remicade called Inflectra might be upsetting the anti-inflammatory apple cart. Inflectra is being sold at a sizable discount to Remicade, which may encourage payers and doctors to shy away from more expensive brands like Enbrel and Remicade moving forward. 

Second, biosimilar versions of Amgen's white blood-cell booster Neulasta are expected to enter the market within a year or so. Though Amgen did get lucky recently when the FDA rejected Coherus Biosciences' (NASDAQ:CHRS) biosimilar CHS-1701, there is no doubt that Neulasta's days of composing a fifth of Amgen's annual revenue are close to coming to an end. 

Finally, Amgen's novel cholesterol drug Repatha has yet to show definitive signs that it's truly a blockbuster-in-waiting that can offset any losses stemming from the company's legacy products facing competition from biosimilars. In the first quarter of 2017, for example, Repatha only generated $49 million in global sales. 

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The company's overarching counterarguments against these real and perceived threats are twofold.

Amgen's management has argued that both Enbrel and Neulasta should still continue to provide substantial free cash flow to the company in the years to come that can be used to fund other value-creating activities such as dividend increases, share repurchases, and of course, additional research and development.

On the Repatha front, the company's defense is that this drug only recently produced positive top-line results in its all-important cardiovascular outcomes trial, which should, in turn, compel payers to provide broader coverage moving forward. 

Analysts basically think Amgen's strengths and weaknesses will produce a wash in terms of top-line growth in 2018. Further regulatory delays regarding the entry of either Coherus Biosciences' CHS-1701 and other biosimilar candidates for Neulasta, though, could produce modest single-digit growth for the biotech next year. 

What's the verdict? Despite Amgen's faltering legacy products business, the company does have an unusually strong pipeline, a top-tier dividend, and management has worked diligently at improving gross margin across the board, which has resulted in a nice uptick in free cash flow over the past year. So while this top biotech stock may be out of favor with investors at the moment, bargain hunters with a longer-term mindset might want to consider adding Amgen to their portfolios right now. 

Celgene is in "prove it" mode

Celgene's stock is cheap for two reasons. The first is that Celgene is projected to grow its top line by a whopping 16.8% next year, thanks in large part to the smashing success of inflammatory disease drug Otezla. In other words, the biotech's top and bottom lines are growing at a remarkable rate that isn't being totally appreciated by the market right now.

On the flip side, investors are also apparently concerned about the longevity of the biotech's double-digit revenue growth due to the mixed bag of top-line results for its experimental relapsing multiple sclerosis drug ozanimod, and the string of safety issues hitting its adoptive cell therapy partner Juno Therapeutics. These two key clinical-stage programs are expected to play an immense role in keeping Celgene in the upper echelon of biotech growth stocks over the next decade.

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These clinical hiccups are probably being overemphasized by the market due to the uncertainty coming out of Washington, D.C., regarding President Trump's corporate tax reforms and the possibility of a major overhaul concerning prescription drug prices. Celgene, however, is well-positioned to meet its longer-term financial results.

This biotech is on track to produce 19 pivotal stage data readouts over the next two years, and is advancing an enormous 180 clinical trials for 30 novel agents at the moment. That's pretty much tops in the industry from an R&D standpoint and a big reason why Celgene has been able to consistently deliver double-digit growth over the past decade. Most importantly, the biotech's flood of clinical activity implies that it can avoid any major drug pricing reforms by relying on sizable increases in product sales across its portfolio as a whole. 

Celgene is arguably always a great biotech stock to buy because of its unwavering commitment to R&D. Like all other high-output biotechs, the company is going to run into the ditch on occasion when it comes to producing novel products that are well-differentiated in their field. But the company more than makes up for its clinical setbacks by taking a strength-in-numbers approach to drug discovery and development. And that's why Celgene is potentially a fantastic buy for investors on the hunt for compelling value plays in biotech.

George Budwell owns shares of Pfizer. The Motley Fool owns shares of and recommends Celgene and Johnson & Johnson. The Motley Fool recommends Juno Therapeutics. The Motley Fool has a disclosure policy.