To catch up with rivals in creating drugs that hit a target called hsp90 (heat shock protein 90), Pfizer bought an outfit called Serenex.

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The vaccine works -- he hopes -- by targeting something called a heat-shock protein, which is produced in high quantity by tumor cells.

CNN: Vaccine may shift odds against deadly brain cancer

Like Antigenics' other cancer therapies, the vaccine programs the immune system to recognize a particular molecule present in many kinds of cancer, called a heat-shock protein.

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