Editor's note: A previous version of this article incorrectly stated that lintuzumab was an antibody-drug conjugate and also did not mention SGN-CD33A. It also incorrectly stated that Gleevec and Bosulif were tested head to head in a clinical trial. The Fool regrets the errors.

As I noted 11 weeks ago, cancer statistics are both staggering and disappointing. Although cancer deaths per 100,000 people have been on the downswing since 1991 thanks to access to more effective medications and better awareness about the negative health effects of smoking, there is still a lot of research and progress yet to achieve. My focus in this 12-week series is to bring to light both the need for continued research in these fields, as well as highlight ways you can profit from the biggest current and upcoming players in each area.

Over the past 10 weeks, we've looked at the 10 cancer types most expected to be diagnosed this year:

Today, we'll turn our attention to the projected 11th-most diagnosed cancer: leukemia.

The skinny on leukemia
This year, nearly 49,000 new cases of leukemia are expected to be diagnosed. While that's well below some of the previous cancer's we've examined, the virulence of leukemia -- which is a cancer of the bone marrow or blood -- is higher than many we've reviewed in recent weeks. Leukemia is forecast to claim close to 24,000 lives this year, which makes it the sixth-deadliest cancer for both men and women.

There are four primary types of leukemia: acute lymphocytic leukemia (ALL), which is a cancer that starts from white blood cells called lymphocytes and is most common among children; acute myeloid leukemia (AML), which is a cancer usually found in adults where the bone marrow makes abnormal myeloblasts; chronic myeloid leukemia (CML), which is where the bone marrow makes too many white blood cells; and chronic lymphocytic leukemia (CLL), which is the most common adulthood leukemia and causes a slow increase in white blood cells called B lymphocytes, which helps spread cancer.

Although early stage detection really doesn't exist unless you're already presenting symptoms (fatigue, paleness, weight loss, bruising easily, etc.) or happen to be in the right place at the right time and are diagnosed during a blood test, the curability and severity of symptoms depends on which of these four diseases you have. Five-year survival rates for all leukemias have increased dramatically, from 34% in 1975-1977 to 58% as of 2002-2008, according to the American Cancer Society (links opens PDF file), but some offer better hope than others. As the ACS notes, those with CLL have an 82% chance of five-year survival, whereas AML patients have just a 25% chance.


Sources: Surveillance, Epidemiology, and End Results Program and the National Center for Health Statistics. 

The risk factors associated with leukemia are just as varying as the statistics with regard to five-year survival. Cigarette smoking, for instance, is a big risk factor for AML, while the probability of CLL has a lot to do with the genetics in your family. One common theme that appears to be a risk factor across all types of leukemia is radiation exposure -- especially through the course of receiving chemotherapy or treating an existing cancer.

Where investment dollars are headed
Although there are numerous medications targeting leukemia, we'll stick to these four most common types listed above. Here's a look at some of the most common therapeutic agents used to treat leukemia.

  • Sprycel: Developed by Bristol-Myers Squibb, Sprycel was approved in 2006 as a second-line treatment for patients who had Philadelphia chromosome-positive (Ph+) ALL or Ph+ CML, and had resistance to prior therapy. In trials, 42% of patients with Ph+ ALL showed a complete or partial response while taking the drug and it delivered a median response time of 4.8 months. 
  • Gleevec: Marketed by Novartis, Gleevec is also a secondary treatment used to treat Ph+ ALL and CML in patients who haven't responded to previous treatments. More recently, Gleevec was granted FDA approval to treat children with Ph+ ALL, which is an important win for Novartis because, as I mentioned, ALL is the most common form of leukemia in children. Gleevec is part of a class of drugs known as tyrosine kinase inhibitors that blocks a protein crucial for cancer cell development. 
  • Iclusig: Approved by the FDA this past December on an accelerated approval basis and developed by Ariad Pharmaceuticals (NASDAQ: ARIA), Iclusig is also approved to treat Ph+ ALL and Ph+ CML. In trials, 54% of patients experienced a major cytogenetic response that had chronic phase CML, while 41% of patients with Ph+ ALL were noted as having a major hematologic response with a median duration time of 3.2 months. Iclusig does come with a black box warning label, though, that arterial thrombosis and liver toxicity have occurred to patients while on the drug.
  • Bosulif: Also approved recently (back in September) and developed by Pfizer (PFE 1.32%), Bosulif is a tablet that targets Ph+ CML in patients with resistance or intolerance to prior treatments. In trials, of those with chronic phase CML, nearly 34% received a major cytogenetic response. Even more impressive, 53.4% of all patients had a major cytogenetic response if they'd previously taken a tyrosine kinase inhibitor, with more than half of these patients demonstrating a response time in excess of 18 months.
  • Erwinaze: Now owned by Jazz Pharmaceuticals via its purchase EUSA Pharma, Erwinaze is more a symptom-treating therapy than a curative agent. Erwinaze is approved for patients with ALL that have developed hypersensitivity to E-coli-derived asparaginase and was given the thumbs up by the FDA based on a single clinical trial involving 58 patients.

I could nearly go on all day with the therapies used to treat leukemia, but these are some of the most common branded names. There are also numerous generic treatments used to treat a broad range of leukemias. However, as we've witnessed previously, not every drug trial turns out to be a success. Seattle Genetics (SGEN), discontinued its trial for a monoclonal antibody drug called lintuzumab in 2010 after it failed to provide a statistical benefit to patients in a mid-stage trial. The company, which admittedly has one of the newest and hottest technological capabilities with its antibody-drug conjugates (ADC) technology, is now developing an ADC called SGN-CD33A for the treatment of AML. However, it is not yet in phase 1 trials, and it will take years to assess this drug’s potential.

What's coming down the pipeline
Now that you have a better idea of what's going in in the world of leukemia treatments, let's have a look at some of the clinical-stage therapies that could be changing lives in hopefully the not-so-distant future.

  • Ibrutinib: There's probably no doubt that Pharmacyclics' (NASDAQ: PCYC) Ibrutinib would take the cake as one of the most exciting pipeline candidates. Currently, it's being tested on mantle cell lymphoma (as we saw last month), and the difficult-to-treat CLL. Partnering with Johnson & Johnson's subsidiary Janssen Pharmaceuticals, Ibrutinib delivered a complete or partial response to 71% of treatment-naive CLL patients, with an incredible 96% of those treatment-naive patients showing no disease progression after two years! The 71% response rate blew every other clinical trial on CLL to date out of the water and was good enough to earn Ibrutinib the very rare "breakthrough therapy" designation from the FDA. 
  • Idelalisib (GS-1101): Currently in early stage development by Gilead Sceinces (GILD -0.09%), Idelalisib blocks the PI3 kinase delta to inhibit tumor growth and hopefully treat its target patient population: those with CLL. In the wake of the annual American Society of Clinical Oncology meeting in less than two weeks, Gilead reported early data from Idelalisib, and the results were phenomenal. More than half of the 54 patients enrolled exhibited meaningful tumor shrinkage, with median progression-free survival of 17 months. It's certainly an experimental drug worth keeping your eyes on. 

Your best investment
As with the treatments, I could spend an entire day talking about what's coming down the pipeline and still might leave a few dozen potential therapies out. What can definitely be said is that researchers and big pharmaceutical companies are certainly throwing their weight around with regard to research into leukemia.

If you were to look at this from an investing perspective, I think you have some clear-cut winners in this space -- although I'd say picking a favorite might be impossible.

Obviously, both experimental drugs have a lot going for them at the moment. Pharmacyclics has a collaborative partnership with J&J's Janssen that could net it up to $975 million in royalty payments. Ibrutinib has performed splendidly in trials, but it'll certainly need to keep those expectations sky high if it wants to support its already frothy valuation.

Gilead offers promise from its existing pipeline of HIV and hepatitis drugs, but is still a long way away from seeing any bottom-line impact from Idelalisib. Make no mistake about what I'm saying here: I like Gilead a lot -- but any real results from Idelalisib are still years down the road.

I think the most solid play in leukemia is Pfizer. For patients who had been previously treating with Novartis' Gleevec and exhibited accelerated CML, Bosulif helped trial patients' blood counts return to normal in 33% of cases. Overall, 55% of patients achieved a normal blood count with no sign of leukemia within the first 48 weeks of treatment. Bosulif offered some of the top progression-free response times and a high cytogenetic response rate, making it the most attractive second-line treatment available -- in my opinion, at least.

Stay tuned next week, when we tackle the current and upcoming therapies for the treatment of pancreatic cancer in this "Tackling Cancer" series.