The American Society of Clinical Oncology annual meeting kicks off today. The scientific conference is the premier place for oncology companies to present data on their cancer drugs. Here are a couple of investment ideas for cancer stocks to watch during the meeting.

Big pharma, big movers
We don't usually associate ASCO investment ideas with big pharma. Sure, they present data each year, but it's hard to identify an investment idea that will actually move a pharma's stock, given their large size. It takes a lot to move the needle.

This year looks like it'll be different. Bristol-Myers Squibb (NYSE:BMY) and Roche (NASDAQOTH:RHHBY) both have drugs that look like they can be mega blockbusters because their compounds can potentially be used to treat multiple types of cancer.

Rather than attacking the cancer directly, where different types of cancer require different targets, Roche's MPDL3280A and Bristol's nivolumab remove a molecular switch that holds back the immune system from attacking the cancer. Both drugs turn off the switch, allowing the immune system to attack the cancer.

I don't necessarily think this mechanism is the cure for cancer, but it does appear to help in a wide range of tumors that all use the same switch to tell the immune system not to attack.

Expanding possibilities
(NASDAQ:EXEL) announced today that it started a phase 3 trial for Cometriq for patients with kidney cancer  The trial will enroll patients who have failed a first-line treatment such as Onyx Pharmaceuticals'  Nexavar or Pfizer's Sutent. Going for the second-line indication is less risky although it cuts down on the market size a bit.

I doubt the timing of the announcement is a coincidence. Exelixis has nine different presentations at ASCO covering Cometriq in different indications. The drug is already approved to treat medullary thyroid cancer that has spread to other parts of the body, but that's a small indication that only affects 500 to 700 patients in the U.S. each year.

Exelixis really needs to expand Cometriq into other indications. Kidney cancer is a good choice and Exelixis is also testing it in prostate cancer. One of the presentations featured at ASCO is an update from its phase 2 prostate cancer trial.

A blood cancer
ASCO is typically about solid tumors while the American Society of Hematology annual meeting focuses on blood cancers like leukemia and lymphoma, but ARIAD Pharmaceuticals (NASDAQ:ARIA) is out in full force with seven presentations for Iclusig.

Like Exelixis, ARIAD wants to expand the use of Iclusig, its treatment for patients with chronic myeloid leukemia, or CML and Philadelphia chromosome positive acute lymphoblastic leukemia, or Ph+ ALL, who have failed or can't tolerate other therapies .

In several presentations at ASCO, investors will get to see data testing Iclusig in first-line setting, including an open-label study comparing it to Novartis' Gleevec in newly diagnosed CML patients and in combination with chemotherapy as a first-line treatment for Ph+ ALL. Grabbing just a portion of Gleevec's blockbuster sales would help justify ARIAD's valuation.

Investment ideas -- stressing the word "idea"
With ASCO going over the weekend, it's easy to get worked up ready to hit the buy button on Monday morning. While there will likely be some stocks that jump at the open, investors should exert some restraint. ASCO pops often come back to earth after the fanfare subsides.

Fool contributor Brian Orelli has no position in any stocks mentioned. The Motley Fool recommends and owns shares of Exelixis. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.