The hate mail poured in when I discussed my

Geron

(GERN) - Get Report

short recommendation

last week, so what will my inbox look like now that I've closed out the Geron short after the stock took another dive Wednesday?

With Geron shares down 11.4% to $5.74 Wednesday, I alerted subscribers to my Biotech Select investment newsletter that I was covering the Geron short recommendation that started on Jan. 26. The final return on the short recommendation was 25%.

The reason for the dive in Geron's stock price Wednesday was the publication of a medical paper detailing the case of a boy with a fatal brain disease who was treated with an experimental concoction of fetal neural stem cells. These fetal stem cells caused benign tumors to grow on his brain and spinal column.

The case was reported last night in the medical journal

PLoS Medicine

and can be downloaded

here

. An MSNBC story on the boy can be found

here

.

This tragic case had nothing to do directly with Geron. The boy was apparently treated with neural stem cells at a clinic in Moscow. He was not enrolled in a clinical trial involving Geron or its stem-cell drug GRNOPC1.

Geron recently received permission from the Food and Drug Administration to begin its own phase I safety study of GRNOPC1 in patients with complete spinal cord injuries. Geron executives have stressed that the company has data showing that GRNOPC1, when injected into rats, does not cause tumor growth.

Still, uncertainty over the safety of such stem cell drugs in humans caused Geron shares to fall Wednesday. Other stem cell stocks, including

StemCells

(STEM)

,

Aastrom BioSciences

(ASTM)

and

Advanced Cell Technologies

(ACTC.PK)

, were also trading lower.

Adam Feuerstein writes regularly for TheStreet.com. In keeping with TSC's editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet.com. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback;

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