ORLANDO, Fla. -- One of the reasons close attention is paid to the annual meeting of the American Society of Clinical Oncology is to hear from companies that are developing entirely new ways of fighting cancer. Monday, it's

Millennium Pharmaceuticals'

(MLNM)

turn in the spotlight.

The Cambridge, Mass.-based biotech firm is developing the first proteasome inhibitor, dubbed MLN341, for use against cancer. More on how the drug works later, first the positive results from a Phase II clinical trial: MLN341 was able to significantly reduce the amount of cancerous material in the blood, known as the tumor burden, in some patients with very advanced stages of multiple myeloma, a common blood cancer.

Many of these patients had depleted all existing medical options, having failed as many as five prior treatments for the disease.

"MLN341 has been shown in this study to arrest the course of the disease and delay disease progression in study patients while avoiding many of the more toxic and debilitating side effects common with standard treatments," said Dr. Ken Anderson of the Dana-Farber Cancer Institute, and lead author of the MLN341 study.

Millennium was expected to deliver some of the better news at this year's ASCO meeting, based on data previously released about the drug. A sneak peek of MLN341's potential was also found in research abstracts

leaked to Wall Street prior to ASCO's start.

More Data Coming

But some caution is warranted. The data released Monday on MLN341 are preliminary, from 78 of 202 patients in the Phase II trial. Millennium also plans to perform a randomized, controlled Phase III clinical trial before the drug is ready for submission to the Food and Drug Administration. The company expects to start this study by the end of June.

Of the 78 multiple myeloma patients treated in this stage of the study, 20% had a greater than 90% reduction in their M protein level -- a substance in the blood used to evaluate tumor burden. Another 27% of patients experienced M protein reduction of between 25% and 90%.

Overall, 77% patients receiving MLN341 experienced a reduction or stabilization of their M protein level during the 24 weeks of the study. A majority of these patients have been able to keep their cancer from progressing.

Side effects from the drug were predictable and manageable, although two patients were forced out of the study because of pain and numbness in their arms and legs, known as peripheral neuropathy, the company said. (A large majority of patients entered the trial with some degree of this condition.)

As mentioned above, MLN341 is a novel cancer-fighting drug. Proteasomes are enzymes in cells responsible for breaking down a variety of proteins, including many that regulate cell division. If proteasomes do not function properly, they can halt cell division, ultimately causing cells to die.

The theory behind MLN341 is that it works by inhibiting the function of the proteasome, which stops cancer cells from dividing, causing them to die. Proteasomes are present in every cell in the body, but researchers believe cancer cells are particularly sensitive to the effects of proteasome inhibition, while healthy cells appear able to recover from the effects.

Millennium released the results from the Phase II study of MLN341 Monday morning at an ASCO poster presentation. A more detailed discussion of the drug will take place later Monday.

In a report written before ASCO and based on the MLN341 abstract, Robertson Stephens biotech analyst Mike King said he expected the drug's results "suggest a powerful response rate in a heavily pre-treated patient population. We are encouraged by this and believe MLN-341 is well on its way to becoming a product and potentially an adjunctive drug of choice for the treatment of cancer." King rates Millennium a strong buy; his firm has a banking relationship with the company.

Multiple myeloma is the second-most common form of blood cancer, but in order for MLN341 to become a blockbuster cancer drug, most analysts believe it must prove effective in fighting solid tumors as well. Tuesday, Millennium is expected to discuss preliminary findings from two Phase I studies studying the safety and limited efficacy of MLN341 when given in combination with chemotherapy to patients with advanced pancreatic, lung and colorectal cancer.

Millennium closed Friday at $18.88 per share.