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Americans have a veritable bounty of retirement tools to choose from, but arguably none is better than the Roth IRA.

A Roth IRA is a tax-advantaged retirement tool open to a majority of Americans. Only individuals making more than $132,000 in adjusted gross income, and joint-filers earning more than $194,000, in 2016 are excluded from participating. This means that nearly nine in 10 people in the U.S. have the opportunity to open, and contribute to, a Roth IRA.

The clearest advantage of the Roth IRA is that investment gains within the account are free and clear of taxation for life, so long as you don't make any unqualified withdrawals. Certain tax-advantaged retirement tools, such as an employer-sponsored 401(k) or Traditional IRA, only defer your taxes until you begin making withdrawals. Since a Roth is funded with after-tax dollars, any gains made are yours to keep once you reach age 59 1/2.

A Roth IRA also offers exceptional financial flexibility:

  • Contributions (not to be confused with investment gains) to a Roth can be withdrawn at any time, for any reason, without tax or penalty.
  • There's no age limit on when contributions to a Roth IRA must cease, unlike a Traditional IRA, where contributions must cease in the year you turn 70.
  • There are no minimum distribution requirements with a Roth, meaning you're free as a senior to take distributions on your own schedule, or not at all.

These incredible tax and flexibility advantages often encourage investors to load up their Roth IRAs with brand-name, dividend-paying stocks that can allow them to take advantage of compounding through reinvestment over time.

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You could be overlooking this gem of a stock for your Roth IRA

But if you're focused solely on dividend-paying brand-name stocks, you're probably overlooking an incredibly attractive growth stock in one of the most volatile industries, biotech. I'm talking about none other than biotech blue chip Celgene (NASDAQ:CELG).

There's no two ways about it: Celgene's management understands that shareholders would like to see the company pay a dividend, but they have no intention of doing so anytime soon for reasons we're going to get to below. Between the volatility of biotech stocks, in general, and the lack of a dividend, some Roth IRA accountholders might be passing up what looks to be an exceptional bargain.

Celgene offers three channels to long-term growth that should get investors excited.

Piling on the organic growth

First, Celgene has been demonstrating phenomenal organic growth, which itself has taken two forms. Celgene has grown its existing products by traditional means of marketing and increasing sales, and it's also expanded the label indications of its core products to lift its sales ceiling.

Image source: Celgene.

At the heart of Celgene's success is blockbuster multiple myeloma drug Revlimid, which is administered in first- and second-line chemotherapy regimens. Based on Celgene's most recent quarterly report, Revlimid is on track for $6.8 billion in sales this year, and it remains on pace for double-digit growth perhaps through the remainder of the decade. A growing number of multiple myeloma diagnoses, strong pricing power, longer duration of use, and dominant market share, continue to fuel sales of Celgene's leading drug.

Just as important to Revlimid's growing sales is the fact that Celgene locked up those sales for another decade. In December, Celgene settled litigation with three generic drugmakers who were challenging Revlimid's patents. The settlement reached allows Natco Pharma to begin offering a small amount of generic Revlimid beginning in March 2022, with incremental increases through March 2025. However, a flood of generic entrants isn't expected until January 2026. This settlement should allow Revlimid to make a run at, if not surpass, $10 billion in sales per year by 2020, as well as sustain these high sale levels for years to come.

Image source: Celgene.

Beyond Revlimid, Celgene has its rapidly growing oral anti-inflammatory drug Otezla, whose sales nearly tripled to $242 million during Q2 2016 from the year-ago quarter, as well as multiple myeloma drug Pomalyst, which generated $318 million in revenue during Q2, a 35% year-over-year improvement. Sales of breast, lung, and pancreatic cancer drug Abraxane have slowed recently, but possible combinations with cancer immunotherapies could have this roughly $1 billion per year drug back on track very soon.

Huge inorganic growth opportunities

Let's be clear that organic growth opportunities trump all channels of growth in the eyes of Wall Street and investors. However, Celgene has other tricks up its sleeve. While not known as a big acquirer, Celgene has the capability to make moves to further diversify its product portfolio and pipeline.

Image source: Getty Images.

In 2010, Celgene acquired Abraxis BioScience to gain hold of Abraxane, the aforementioned cancer drug that's poised to generate about $1 billion in sales in 2016. But in the year before Celgene's acquisition, Abraxane had generated just $315 million in sales. Label expansions to non-small-cell lung cancer and pancreatic cancer helped push sales substantially higher. 

More recently, in 2015 Celgene announced the $7.2 billion acquisition of clinical-stage drug developer Receptos. The deal allowed Celgene to get its hands on ozanimod, an experimental drug that's shown a lot of promise in treating multiple sclerosis and ulcerative colitis. If approved in both indications, ozanimod could peak at $4 billion to $6 billion in annual sales, which would make its $7.2 billion purchase price look like a bargain. Ozanimod, if approved by the Food and Drug Administration, should also help diversify Celgene's product portfolio, which currently relies on Revlimid for more than 60% of its net product revenue.

Collaborations galore

Just in case Celgene's double-digit organic growth rate and M&A opportunities aren't enough, Celgene also boasts more than 30 ongoing collaborations spanning oncology, immunology, and inflammation. In many instances, Celgene is focusing on first-in-class therapies through potential licensing deals with outside companies.

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If you think about it, Celgene's approach to forge a large number of collaborations is a genius move. Rather than spending billions of extra dollars on internal research and development -- mind you, Celgene is still spending a lot on internal R&D of its own -- Celgene has sort of outsourced its R&D to its partners in exchange for upfront capital in some instances, as well as the promise of milestone payments if experimental drugs reach certain development, regulatory, or sales milestones. Doing so ensures that Celgene throws its capital at only the most promising drugs.

One of its more exciting partnerships is with Agios Pharmaceuticals (NASDAQ:AGIO), a developer of IDH-mutant inhibitors that could be useful in treating acute myeloid leukemia and glioma. Agios has two promising IDH inhibitors in development, AG-120 and AG-221, but it's AG-221, an IDH2-mutant inhibitor, that looks the most promising. When administered to relapsed-refractory acute myeloid leukemia patients, the drug led to a 37% response rate, which would probably be good enough to consider it as a standard-of-care therapy. Licensing AG-221 brought Agios the opportunity to earn up to $120 million in milestone payments, as well as tiered royalties on the drug if it makes it to pharmacy shelves.

Celgene's numerous deals should give it a long-term growth edge over many of its biotech peers.

Fundamentally fabulous

Added together, these three catalysts make Celgene look fundamentally fabulous. Typically, a PEG ratio -- a measure of current price-to-earnings divided by future growth expectations -- of below 1 signals a "cheap" stock. Celgene's current PEG is just 0.9, and that takes into account its recent post-earnings rally.

With operating cash flow of $3.25 billion over the trailing-12-month period, a penchant for repurchasing its own common stock to reward investors, and an expected double-digit growth rate for many years to come, Celgene is a stock that Roth IRA accountholders should strongly consider adding to their portfolio.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.