Great minds of science are convening around the country this week -- and Wall Streeters are scrambling three paces behind, sending biotech stocks aquiver.

Centocor

(CNTO)

, meant to star at the

American Heart Association

meeting in Orlando, has run into surprising trouble at the

American College of Rheumatology

meeting in Washington, D.C., and investors sent the stock way down. Longtime Centocor bull Eric Hecht of

Merrill Lynch

downgraded the stock to accumulate from buy, citing concerns about side effects caused by its anti-inflammatory drug

Avakine

. Centocor was off 9 to 43 on heavy volume at midday.

Centocor rival

Immunex

(IMNX)

, shining at the ACR, shot up to 73 1/4 before retreating. At midday, Immunex was up 1 at 69. Centocor's backers went to AHA while Immunex fans went to ACR -- so everyone's scrambling to find out what happened at the respective meetings.

According to Alex To, analyst at

Donaldson Lufkin & Jenrette

and a big bull on Immunex who is considered the "axe" on that stock, Avakine, formerly known as CA-2, has hit a serious stumbling block. In data on 101 rheumatoid arthritis patients treated with its drug in conjunction with methotrexate, a common cancer drug, two patients had serious infections with one dying and one losing an eye. In more than 400 patients treated with the drug for RA, a serious joint inflammation disease, and Crohn's disease, four developed hematopoietic tumors, or congregations of blood cells, To said. To said that methotrexate is known to cause that occasionally, but that while it's a tolerable side effect in cancer patients, it's no good in RA patients. There is also a question of whether Avakine increases the chance of such tumors, said To. Merrill analysts said it was unclear whether Avakine increases the incidence of such tumors.

Avakine is trailing Immunex's

Enbrel

in development for RA treatment. However, the drug is expected to get approval for the small number of patients who suffer from severe Crohn's disease, an inflammatory bowel ailment. Centocor plans to file for approval of Avakine imminently for this application, but To said that it's no longer a sure thing that it will be approved. "This could potentially harm the Crohn's application," said To. Centocor was not immediately available to comment.

Merrill Lynch analyst Doug Melancon, who works with Hecht, said the side-effect problem was unlikely to derail Avakine's application. But for patients with less serious Crohn's disease, the company might have to present additional safety data, he said.

Also at the ACR meeting, Immunex scientists presented Enbrel Phase III data from its study previously announced in September as positive. While there were no surprises, To said, what was important was that in follow-up data in patients treated out to one year with Enbrel, the drug was shown to be effective and have no serious infections and did not cause the development of antibodies that would neutralize the drug, a concern with all such therapies, To said.

Separately, in the sunny climes of Florida, Centocor presented data from a study, called TIMI 14, comparing use of the "super-aspirin"

ReoPro

in conjunction with clot-busting agents, such as

Genentech's

(GNE) - Get Report

tPA. The drug, already on the market for angioplasty patients, is sold by

Eli Lilly

(LLY) - Get Report

.

Genentech's drug alone did better than ReoPro alone and streptokinase, another clot-buster. But ReoPro along with a lowered dose of tPA showed slightly better results than tPA alone.

Furman Selz

analyst Jon Alsenas, a big Centocor bull, declared that the interim results showed that ReoPro was on its way to becoming the standard of care in heart attacks. But others were not nearly as impressed -- which also led to weakness in the stock -- contending that it would take stronger data to convince cardiologists to use the expensive ReoPro.

Also at AHA,

Cor Therapeutics

(CORR) - Get Report

presented full results of its Phase III trial with

Integrilin

in unstable angina patients. The initial conclusions were presented in late August. Integrilin is in the same antiplatelet class as ReoPro, a group of drugs also known as super-aspirins. In the largest study ever of such a drug in unstable angina patients, Integrilin was shown to be effective, though whether the effect is strong enough to outclass ReoPro is a matter of debate among investors. Cor was up 9/16 to 23 1/2 at midday.