A therapeutic cancer vaccine from Oxford BioMedica that failed in a clinical study may still help a subset of patients, researchers said on Tuesday.

Shares in the company plunged as much as 18 percent in early trade as investors reacted to the reiterated trial failure rather than the fact the drug, TroVax, may help some patients, analysts said.

This is a classic case of the market reading the headline (old news) and not understanding the real implication of the detailed data, said Ian Wainwright, Managing Director of Life Sciences Specialist Sales at Canaccord Adams.

(The data) in fact shows TroVax works if you pre-select patients most likely to respond via a blood test.

The original failure prompted French drugmaker Sanofi Aventis to hand back rights to TroVax in April. The latest data suggested it may yet have a future and could kindle renewed interest from potential pharmaceutical partners.

Although TroVax did not show a significant survival advantage in the overall population studied, patients with a good prognostic profile receiving interleukin-2 therapy did live longer, results at the ECCO-ESMO cancer conference showed.

Robert Hawkins of the Christie Hospital in Manchester said a specific immune response, known as anti-5T4, induced by TroVax was associated with enhanced survival.

Although I am disappointed that the trial did not meet its primary endpoint, I believe that TroVax is still of potential benefit to patients with cancer and I hope further studies will be initiated with more refined target populations, he said.

The company's chief executive, John Dawson, said he aimed to hold talks with prospective partners and the oncology community in order to start fresh trials of TroVax as soon as possible.

Shares in Oxford BioMedica pulled back to trade down 6 percent at 11.5 pence by 0818 GMT.