Shares of

ImmunoGen

(IMGN) - Get Report

jumped 8% on Friday afternoon after the biopharmaceutical company said that

British Biotech

(BBIOY)

would pay $1.5 million for the rights to develop and market ImmunoGen's treatment for small cell lung cancer, a particularly aggressive form of the disease.

ImmunoGen's stock was up 13/16 to 11 5/16. The news comes the day after the Cambridge, Mass.-based company had announced that

Genentech

(DNA)

, one of the world's largest biotechnology companies, had paid $2 million for the exclusive rights to market a separate anti-ancer drug for use with Genentech antibodies like Herceptin.

ImmunoGen combines a drug and antibody to form the huN901-DM1 tumor-activated prodrug, which kills cancer cells more efficiently. British Biotech has the exclusive rights to the product in the European Union and Japan and is responsible for conducting the clinical trials for regulatory approval in the U.S., EU and Japan. ImmunoGen retains rights in the U.S. and will handle the remaining preclinical development.

Carl Gordon, a general partner at

OrbiMed Advisors

, was more impressed with the Genentech deal. "If Genentech is interested in using ImmunoGen's technology, that's the best validation you can get," he said. He has no official rating on ImmunoGen and his firm does not participate in underwriting.

He was less impressed with the British Biotech deal, only because the Oxford-based company has stumbled of late, with its stock diving 66% in the last two years. It has experienced problems with its two leading drugs: Zacutex, a treatment for acute pancreatitis, and marimastat, a pancreatic cancer treatment. The chief executive and the director of research and development have also departed the company.

There are also a number of other very strong cancer-treatment companies that could have been potential partners, Gordon said, including

Bristol-Myers Squibb

(BMY) - Get Report

,

Pharmacia

(PHA)

and

AstraZeneca

(AZN) - Get Report

.

But Mitchel Sayare, chairman and chief executive of ImmunoGen, said in an interview, "With the bigger companies, we had to give up the worldwide rights." He also said that British Biotech has the most experience in conducting clinical trials in small cell lung cancer.

It remains to be seen whether ImmunoGen's products will result in a significant breakthrough for a cancer cure.

Shares of British Biotech closed trading on the

London Stock Exchange

at 27 pence, up .75 pence or 3%. The company's American depositary receipts fell 1/8, or 3%, to 3 5/8 in midday Friday trading.