Threshold's Pancreatic Cancer Drug Boosts Survival -- With an Asterisk

Updated with new information.

SOUTH SAN FRANCISCO ( TheStreet) -- Threshold Pharmaceuticals' ( THLD) TH-302 boosted the survival of pancreatic patients, but data from the mid-stage study raised concerns and caused the stock to fall.

At the median, TH-302 survival data are impressive. The combination of a higher dose of TH-302 plus gemcitabine yielded a median overall survival of 9.2 months versus 6.9 months for gemcitabine alone. That's a median survival benefit of 2.3 months, which is meaningful for any pancreatic cancer trial. Consider that Roche and Astellas' Tarceva was approved in pancreatic cancer based on a two-week survival benefit.

The broader survival analysis of the same Threshold study does not look as favorable, however. Adding TH-302 to gemcitabine only reduced the relative risk of death by 4.5% over gemcitabine alone -- a small benefit that was far from statistical significance.

Threshold shares fell $1.67 or 19% to $7.05 in Monday trading, sparking conversation on Twitter over how best to evaluate TH-302 and its potential in pancreatic cancer.

Based on these phase II data, Threshold and partner Merck KGaA are in the process of designing a phase III study of TH-302 in pancreatic cancer.

Threshold announced the survival data from the TH-302 phase II pancreatic cancer study Monday in advance of presentation at the European Society of Medical Oncology meeting on Sept. 29.

This phase II study enrolled 214 pancreatic cancer patients and randomized them to treatment with TH-302/gemcitabine or gemcitabine alone. As presented earlier this year, treatment with TH-302/gemcitabine led to a two-month improvement in progression-free survival of 5.6 months compared to 3.6 months for gemcitabine alone. The benefit in PFS was statistically significant, although there were some imbalances in patients' baseline criteria that favored TH-302 and may have skewed results.

Approximately one-third of patients in the gemcitabine arm "crossed over" to receive TH-302 after tumor progression. Threshold says this crossover did contribute to an increase in survival in the study's control arm. In older studies, including the pivotal study of Tarceva, patients treated with gemcitabine lived about six months.

Celgene ( CELG), Clovis Oncology ( CLVS) and Peregrine Pharmaceuticals ( PPHM) are expected to announce results from their own closely watched pancreatic cancer drug trials before the end of the year.

Prior to Monday's fall, Threshold shares were up more than 500% this year based on optimism for TH-302.

--Written by Adam Feuerstein in Boston.

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Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.