Many stocks encountered turbulence this week, but few were blown about like several biotech stocks. Here are the three most horrendous performers in health care over the first week of June.

Underwhelming
Synta Pharmaceuticals (NASDAQ: SNTA) announced results from a mid-stage clinical study this week for lung cancer drug ganetespib. Shares plunged 38% as investors reacted. Did the drug fail completely? Actually, no.

Patients taking a combination of ganetespib and the chemotherapy docetaxel lived a median of 9.8 months. Other patients taking only docetaxel lived a median of 7.4 months. That's a 32% improvement. Even better improvement of 67% was experienced by patients whose cancer was diagnosed at least six months before the initiation of the study. Synta's results sound really good, right?

There are a couple of problems, though. First, results from the study announced late last year indicated more dramatic improvement. Second, the difference in numbers of patient deaths between the two groups of patients is small. Investors appear to be losing confidence that ganetespib will live up to earlier expectations.

No win for the spin
Another biotech, Infinity Pharmaceuticals (INFI), also announced clinical results this week. The company's press release trumpeted "encouraging" findings for its experimental leukemia drug. Mr. Market didn't appear to buy the spin. Infinity shares tanked nearly 33% for the week.

The catalyst behind the sell-off stemmed from safety concerns about IPI-145, the drug tested in the phase 1 study. Some patients who took the treatment died, although Dr. Steven Horwitz of the Memorial Sloan-Kettering Cancer Center pointed out early in the week that these patients had undergone transplants and were very ill.

Another issue is fear over potential rivals. Gilead Sciences (GILD -0.43%), for example, reported in May that its idelalisib produced significant tumor shrinkage in half of the patients involved in an early-stage trial. Dr. Sandra Swain, president of the American Society of Clinical Oncology, called the results "pretty incredible." Gilead is also testing idelalisib in the treatment of non-Hodgkin's lymphoma.

Pain-medication pain
Rigel Pharmaceuticals (RIGL -0.44%) experienced pain this week, resulting from its drug intended to help rheumatoid arthritis patients suffer less pain. Shares fell almost 23%.

AstraZeneca (AZN 0.20%), which has partnered with Rigel on fostamatinib, opted to turn all rights for the drug back over to Rigel. The British drugmaker decided not to pursue an approval path for the drug after disappointing clinical results. AstraZeneca will take a $140 million hit in the second quarter from the move.

The fallout hurts Rigel even more, though. The small biotech has no other drugs on the market. Rigel certainly faces tough challenges in the days ahead.

Bright spot
I'm usually an optimist and try to find the bright spot in most situations. Which of these horrendous stocks for the week is most likely to see better days ahead?

It's a tough question, but my hunch is to go with Infinity. If the safety concerns about IPI-145 turn out to be overblown, the stock looks to have plenty of room to run. That being said, Infinity carries plenty of risk. Investors looking for the glass of water that's half full should be cautious before taking a big gulp.