Updated from 5:31 p.m. EST Sunday.

Allos Therapeutics

(ALTH)

reported that 27% of patients with a rare but aggressive form of blood cancer responded to treatment with the company's experimental drug pralatrexate.

The patients took part in a pivotal phase II study, the results of which Allos announced Sunday.

The Westminster, Co.-based drug firm said it intends to submit pralatrexate for approval to the U.S. Food and Drug Administration during the first half of 2009.

The phase II study enrolled 115 patients previously treated for peripheral T-cell lymphoma (PTCL), a fast-growing cancer that affects white blood cells known as T-cells. There are no approved drugs to treat the disease.

Of the 109 patients available for evaluation in the study, 29 patients, or 27%, responded to treatment with pralatrexate, including 11 patients whose cancer went into complete remission, according to Allos.

The median duration of response for the entire study has not yet been assessed, but Allos said that for patients who responded to pralatrexate, the median duration of treatment was about six months.

Allos announced the results from the pralatrexate study via press release Sunday. A full presentation of the data will be made Monday morning at the American Society of Hematology annual meeting.

Investors were looking for a pralatrexate response rate from the PTCL study in the 25-30% range in order to be robust enough to garner FDA approval. Last May, an interim analysis from the first 65 patients in the study yielded a 29% response rate.

Allos will be able to submit pralatrexate for FDA approval based on this small phase II study because PTCL is diagnosed in only about 5,000 U.S. patients each year. The FDA didn't require Allos to compare the response rate of pralatrexate to another drug in the study because all the enrolled patients were previously treated, most multiple times, without success.

Pralatrexate, or PDX, is a chemotherapy drug known as an "antifolate" that works by interfering with the ability of cancer cells to divide, resulting in cell death. Allos designed pralatrexate to be more potent than other antifolates, including the widely used drug methotrexate.

Eli Lilly's

(LLY) - Get Report

cancer drug Alimta is another antifolate, approved for the treatment of lung cancer.

Allos is also testing pralatrexate in other forms of non-Hodgkin's lymphoma and lung cancer. One of the lung cancer studies under way pits pralatrexate head to head against Tarceva, a lung cancer drug marketed by

OSI Pharmaceuticals

(OSIP)

and

Genentech

(DNA)

.

Allos shares closed Friday at $6.38 and were down $1.30, or 20.4%, to $5.08, in early trading Monday.

At the time of publication, Feuerstein's Biotech Select model portfolio was long DNA.

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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