Over the years, we have watched many times as incremental gains in early stage research have been transformed by the magic of the media and the markets into remarkable increases in the stock prices and market capitalization of biotech companies.

One of the most memorable examples in recent years was the $735 million increase in Amgen Inc.'s market cap the week of a preclinical publication on its leptin (ob) gene. That was in 1995, and leptin still is only in Phase I development.

Tiny PPL Therapeutics plc's market cap rose 53 percent from £76 million to £116 million (US$185 million) in the week after it announced that it had successfully cloned a sheep from an adult cell. The shares (LSE:PTH) are now below where they started, giving the company a market cap of £48 million.

The latest example was the 34 percent runup in Geron Corp.'s shares last week as a result of the publication in Science of the ability of telomerase to extend the replicative capacity of cells in culture (see Technology Focus, A2). GERN's market cap thus went from $108 million to $145 million on more than 17 million shares traded in the week.

It does not bother us that naive retail investors are quick to equate science to products - they're allowed to dream. Nor does it raise our hackles when smart traders are able to exploit a transitory spike in a stock based on news-driven buying. But we are really troubled when these rocket ships are propelled by the enthusiastic statements of scientists and companies, often without the balancing perspective on the actual timelines involved.

Publicly held companies at early stages of development have little else to move their stock prices, and academe has learned to play the PR game in the hunt for sponsors and research funding. But the fallout from these events does no favors for the industry. Incautious claims about scientific progress not only make it difficult to evaluate the true significance of preclinical results