What to watch at the world's largest cancer research conference

ASCO, the world's largest cancer research conference, starts Friday in Chicago, where oncologists, investors and pharmaceutical executives converge to discuss the latest advancements in treatment.

Immunotherapies, medicines that enable the immune system to better fight cancer, will continue to be a top focus of the conference. Merck (NYSE: MRK), Bristol-Myers (NYSE: BMY), Roche (Swiss Exchange: ROG-CH), AstraZeneca (London Stock Exchange: AZN-GB), Pfizer (NYSE: PFE) and others are working in the space, which BMO Capital Markets analyst Alex Arfaei estimates may be worth $30 billion by 2020. The cost to treat cancer is sure also to be a major topic.

But it's the smaller companies that often see the biggest stock moves out of ASCO (which stands for the American Society of Clinical Oncology). Already the Nasdaq Biotech Index (NASDAQ: .NBI) has rallied into the conference, gaining 6 percent in the last five days. Yet many analysts say this year's meeting looks to be a slower one from an investment perspective. So we decided to ask Kensho, a market data analytics system, what history tells us to expect from ASCO stock performance.

Looking at ASCO meetings since 2011, and a lengthy list of presenting companies with market values of at least $1 billion from a JPMorgan research note, here's what we found:

The most consistently positive performers out of ASCO are Seattle Genetics (NASDAQ: SGEN), Regeneron (NASDAQ: REGN), Ariad (NASDAQ: ARIA), Ionis Pharmaceuticals (NASDAQ: IONS) and Halozyme Therapeutics (NASDAQ: HALO), which traded up at least four years out of the last five (or 80 percent of the time). That's if investors bought the stock the first day of the conference and sold a week afterwards.

Some of those companies will be closely watched at this year's conference as well: Ariad, for new data on its experimental lung cancer drug, brigatinib, and Seattle Genetics, both for data from a competitor in Hodgkin's lymphoma and for one of its internal programs in urothelial cancer, according to RBC Capital Markets.

Another way to track stock performance out of ASCO is a relatively new exchange-traded fund focused exclusively on companies working in immunotherapy, the CNCR Immunotherapy ETF (NASDAQ: CNCR). Started by investor Brad Loncar, it's also rallied into the conference, returning more than 13 percent since initial datasets were released ahead of the conference May 18.

(Source: Loncar Investments. Data as of Thursday's close.)

As for biotech stocks more broadly, Kensho tells us the IBB, the ETF that tracks the Nasdaq Biotech Index, historically only slightly outperforms the broader market through ASCO, returning an average of 0.64 percent from the first day of the conference to a week later, versus 0.56 percent for the S&P 500 (INDEX: .SPX).

Disclosure: NBCUniversal, parent of CNBC, is aminority investor in Kensho.

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