Image source: National Cancer Institute.

If you want to look up the meaning of the word "indecisive," look no further than the trading action in biotech blue-chip stock Celgene (CELG) in 2015. Shares of the drug giant, despite substantial sales and EPS growth, are down less than 1% year-to-date through Dec. 22. At one point Celgene shares were up nearly 25% for the year before they gave back all their gains and then some during the fall.

Celgene delivers strong growth
The indecisive trading might have some people thinking Celgene had an "off" year -- but that's far from the case. Celgene actually delivered 19.8% total revenue growth through the first nine months of the year, and it has its dynamic trio of drugs to thank for its robust growth.

Image source: Celgene.

The newest therapy in Celgene's pipeline is Otezla, an oral medication designed to treat moderate to severe plaque psoriasis, as well as psoriatic arthritis. In the third quarter, Otezla sales jumped to $138.7 million from just $17.6 million in the year-ago period, and total sales through nine months are up to $288.7 million worldwide. Extrapolating out its Q3 totals, and factoring in its volume growth trajectory, Otezla's revenue in 2016 could top $750 million. This is also a drug targeted at a half-dozen other anti-inflammatory indications.

Cancer drug Abraxane, which is used to treat advanced breast cancer and pancreatic cancer, and first-line advanced non-small cell lung cancer, has had a bit of a rougher year despite global sales growth of 13.9% to $697.5 million. Sales in the U.S. are up only 4.7%, likely due to the emergence of cancer immunotherapies, many of which are being tested with treatment pathways similar to those Abraxane would normally use. Immunotherapies have delivered superior response and survival rates to patients with high PD-L1 tumor expression, and Abraxane could find growth in the U.S. slower than anticipated in the coming quarters.

Unequivocally Celgene's best drug in 2015
But when it comes to Celgene's best drug in 2015, there's little denying that multiple myeloma drug Revlimid once again takes the cake.

Image source: Celgene.

Through the first nine months of 2015, Revlimid has generated $4.24 billion in sales, up nearly 18% worldwide on an operating basis. In addition to more than a half-dozen ongoing studies with Revlimid that could further expand its label, the drug continues to amass substantial market share and maintain strong pricing power in its given indications as a first- and second-line treatment for multiple myeloma.

Also working in Celgene's favor is that it's been, until recently, largely shielded from new competition. For example, Amgen (AMGN -0.07%) announced in July that the Food and Drug Administration had granted multiple myeloma drug Kyprolis a label expansion to treat patients who've progressed on one-to-three prior therapies. Initially you'd think that's bad news for Celgene, which has made quite a home for itself as a second-line indication. However, Amgen's Kyprolis is to be administered in conjunction with Revlimid and dexamethasone, meaning Celgene really isn't losing its share. If anything, it's found another solution to potentially add multiple myeloma market share, and both it and Amgen can benefit side-by-side.

The one puzzle piece that could be something of a question mark for Revlimid's growth is the recently approved Darzalex from Johnson & Johnson (JNJ 0.84%) and Genmab. Darzalex, as of now, is approved as a third-line and higher multiple myeloma therapy, but it has demonstrated a higher response rate in clinical studies to Kyprolis (29% versus 23%) in a similar, but not apples-to-apples, clinical comparison. It's possible we could see an expansion into a second-line indication.

Genmab also reported at the American Society of Hematology's annual meeting earlier this month that patients taking the drug had a 90% survival rate at 18 months and 72% of patients taking Darzalex were still experiencing progress-free survival. However, the study presented at ASH was done in combination with Revlimid and dexamethasone, and it could further entrench Revlimid as the go-to multiple myeloma therapy.

In short, don't look for Revlimid sales to slow or be usurped anytime soon.

Image source: Pictures of Money via Flickr.

The only concern with Celgene
Perhaps the biggest drawback of Revlimid is the fact that it represents close to two-thirds of Celgene's revenue. Growth doesn't appear to be an issue at the moment or in the intermediate future, but patent exclusivity periods are finite, and Celgene will eventually need to deal with the introduction of generic competitors. According to a settlement announced by Celgene yesterday, those generics will begin coming on the market in the US in 2022, with broader generic competition opening up in 2026. (Which is still a long ways away.)

Aside from organically growing the label indications of its powerhouse trio, the company has focused on collaborations and an acquisition to bolster its product portfolio and pipeline. The buyout of Receptos for $7.2 billion adds ozanimod, an experimental relapsing multiple sclerosis drug with blockbuster potential, to Celgene's pipeline, and its partnerships with cancer drug developers examining anti-cancer stem cells, CAR-T, and cancer immunotherapies could deliver significant growth if successful.

What investors need to consider here is whether or not Celgene's superior growth can command a higher share price considering that it's so reliant on Revlimid. In my opinion the answer to this question is yes -- not only because of its collaborations and Receptos acquisition, which could diversify its product portfolio, but because of its ability to expand its label indications for Revlimid and really stagger its exclusivity losses over many years. (And with 

For growth seekers, Celgene is a name you'll want to consider adding to your portfolio over the long term.