An experimental cancer vaccine developed by NewLink Genetics (NLNK - Get Report) failed to prolong survival in patients with pancreatic cancer compared to a standard therapy, according to results from a phase III study disclosed Monday.

NewLink shares were halted at $16.50 ahead of the trial results being announced. When trading re-opened, NewLink shares fell 36% to $10.60.

The NewLink vaccine, known as algenpantucel-L, was designed to stimulate a patient's immune system to recognize and kill cancer cells. It did no such thing.

Pancreatic cancer patients treated with algenpantucel-L lived for a median of 27.3 months in NewLink's phase III trial compared to median survival of 30.4 months for patients treated with standard therapy.

The three-month median survival difference went in the wrong direction -- suggesting patients might have been harmed by treatment with algenpantucel-L.

NewLink's statistical plan prohibited independent data monitors from performing an interim futility analysis on algenpantucel-L. Had one been conducted last May during a pre-scheduled safety check, the study might have been terminated early.

Newlink has never explained why it didn't allow independent data monitors to conduct a futility analysis of the algenpantucel-L phase III study, but the absence of one has been profitable for NewLink CEO Charles Link Jr. He sold approximately $9.5 million in company stock since last May, according to SEC filings.

Now that NewLink's therapeutic cancer vaccine platform looks to be a zero, the company's dwindling valuation relies even more heavily on its so-called IDO inhibitors -- another form of cancer immunotherapy -- in early stages of clinical development. The field of companies developing cancer immunotherapies is competitive and crowded.

NewLink shares have lost 70% of their value since hitting an all-time high of $57 last April.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.