Investors know Amgen (NASDAQ:AMGN) primarily for its blockbuster immune system booster Neupogen and anemia therapy Epogen. It may be surprising that a biotech company of this size has no blockbuster cancer-fighting drugs in its arsenal. Well, that's set to change in the months and years ahead. Recent acquisitions of oncology specialists Onyx and BioVex have put Amgen in the ring with Celgene (NASDAQ:CELG), plus pharma heavyweights GlaxoSmithKline (NYSE:GSK) and Merck (NYSE:MRK). Let's take a look at two promising therapies that are instrumental to Amgen's oncology strategy going forward.

This was the main motivation behind Amgen's $10.4 billion purchase of Onyx last year. Some analyst estimates for peak annual sales of the multiple myeloma therapy are over $2.5 billion. To reach that peak there are two major hurdles to jump: label expansion, and competition with Celgene's Pomalyst.

The FDA approved the sale of Kyprolis mid-way through 2012, and Pomalyst about seven months later. Both are indicated for the treatment of multiple myeloma as a third resort. The similarities between the two end there. Taken as a pill, Pomalyst influences the immune system to attack cancer cells and inhibit their growth. Kyprolis is delivered intravenously and acts on cancer cells itself.

So far, it appears the two therapies have a roughly even share of twice-unresponsive patients. Pomalyst is priced slightly higher than Kyprolis. During the first half of 2013, Onyx recorded Krypolis sales of $125 million. During the first nine months of 2013, Celgene recorded Pomalyst sales of about $184 million.

Given their different mechanisms of action, there's a good chance both will continue to share the market. In order for Kyprolis to really drive growth for Amgen and reach blockbuster status, it will probably need to win approval as a second-line treatment.

Currently, Kyprolis is in a Phase 3 trial that, if successful, should lead to that approval. The yardstick used to measure success of the trial is progression free survival at 18 months after treatment. We won't know what the results are until the results are released, and an interim analysis should be completed sometime this year..

Fighting melanoma with herpes?
Kyprolis may be the most prominent part of Amgen's oncology strategy today, but there are several compounds in development that are also worth your attention. One of the most interesting is a novel therapeutic in late-stage development for metastatic melanoma.

T-Vec, short for talimogene laherparepvec, is a re-engineered herpes simplex virus with a dual tumor fighting mechanism. It is designed to infect tumor cells specifically. Once inside, it hijacks the cell's machinery replicating itself until it bursts. T-Vec also causes infected cancer cells to secrete a protein that elicits a local immune response.

In November of last year, Amgen released promising results from an ongoing pivotal Phase 3 trial involving advanced stage melanoma patients treated with T-Vec. The interim data suggests an overall success for the trial looks promising. Amgen expects to release the complete overall survival figures in the first half of this year.

Crowding the melanoma space
If T-Vec wins approval, it will run straight into competition from GlaxoSmithKline, for about half of its indicated patients. Earlier this month, the FDA approved the use of Glaxo's Mekinist and Tafinlar as the first ever combination therapy for metastatic or otherwise inoperable melanoma.

Luckily for Amgen, Glaxo's combo is only approved for patients with tumors exhibiting BRAF mutations. Roughly half of late stage melanoma patients have the mutation, so the other half should be fair game.

If approved, chances are good that T-Vec will also compete with Merck's MK-3475. This exciting new drug limits the ability of tumors to hide from the immune system. Merck is going full throttle in an effort to speed this one to the market. The company initiated an unusually large Phase 1 study with over 1,000 patients, and a rolling submission of its biologics license application..

MK-3475 already has Breakthrough Therapy status, which means the FDA is likely to allow its approval before it completes long-term survival data. With the rolling submission, Merck is feeding regulators data as it becomes available. The immunotherapy could jump ahead of T-Vec in the regulatory process and hit the market first.

Final thoughts
These two therapies aren't the only weapons in Amgen's oncology lineup, but they are a good representation of the most important drugs to watch. So far, the oncology expansion is off to a great start, but at every every turn there is likely to be fierce competition from well funded players. As an investor, you might want to think twice before making any decisions based on the company's cancer therapies alone.

Editor's Note: Results from the ASPIRE clinical trial have not been released yet, and the article has been edited to reflect this. The Fool regrets the error.