Iressa, a lung cancer drug linked to hundreds of deaths since its approval for sale in Japan, could sharply prolong the survival of some patients, researchers said Wednesday.

A team led by Yusuke Nakamura, a professor at the University of Tokyo's Institute of Medical Science, found that patients who are not suited to Iressa have high concentrations of two proteins -- amphiregulin (Areg) and transforming growth factor alpha (TGFA) -- in their blood.

The team studied the relationship between the survival rate of 50 terminally ill lung cancer patients and the presence of the two proteins since August 2002 with the Kanagawa prefectural cancer center and Hiroshima University.

Among 35 patients who tested negative for TGFA and were thought likely to benefit from Iressa, the survival rate after about two years and nine months was 39 percent.

In contrast, all of the 15 patients who tested positive for TGFA died within a year and 10 months after starting treatment with Iressa.

With Areg, the survival rate of those who tested negative for the protein was 25 percent after two years and nine months, while for those who tested positive it was 16 percent after two years and four months, with the former group surviving 2.6 times longer than the latter, the team said.