Threshold's Pancreatic Cancer Drug May be Obsolete Before Launch

Although this analysis suggests the drug is moderately efficacious, the study's unusually wide confidence intervals -- a measure of variability -- and essentially equivocal p values hint at an underlying data unreliability that should worry the bulls. However, even without this clinical red flag, it's hard for me to get excited about TH-302.

For years, no studies showed a clear benefit for gemcitabine-containing combination regimens in pancreatic cancer (a February 2012 paper by Ying et al. in World Journal of Gastroenterology offers a good overview.) Yet some recent evidence suggests the pancreatic cancer treatment landscape may be changing, which could mean trouble for Threshold.

Let's take a closer look at a large European study published in the May 2011 New England Journal of Medicine (Conroy et al. NEJM 2011; 364:1817-1825).

In this trial, investigators randomized 342 patients to either FOLFIRINOX -- a combination chemotherapy regimen including leucovorin (FOL), fluorouracil (F), irinotecan (IRIN), and oxaliplatin (OX) -- or gemcitabine. Despite increased toxicity, FOLFIRINOX significantly improved ORR (31.6% versus 9.4%), PFS (6.4 months versus 3.3 months), and median survival (11.1 months versus 6.8 months) compared to gemcitabine.

Key efficacy metrics for the gemcitabine control group in the NEJM study almost exactly match those in the Threshold TH-302 trial with good reason: The two studies enrolled a nearly identical population of pancreatic cancer patients.

Most oncology studies use Eastern Cooperative Oncology Group (ECOG) performance status as a measure of a patient's well being, with lower scores indicating less disability. In Threshold's study, 30%, 45%, and 39% of patients in the control, low, and high dose TH-302 groups, respectively, had an ECOG score of zero, meaning the patient is "fully active, able to carry on all pre-disease performance without restriction." This closely matches the ECOG scores from the NEJM study (37% and 39% for the FOLFIRINOX and gemcitabine arms, respectively, had an ECOG score of zero).

Other baseline factors, including median age and male gender, were also similar. In fact, a few variables suggest patients in the NEJM study may have been slightly sicker than those in the Threshold trial. Fewer of the NEJM patients had a primary tumor in the pancreatic head -- some studies indicate a slightly more favorable prognosis for masses in this location, which is near the bile duct -- and more had liver metastases. Despite the obvious limitations of cross-study comparisons, the groups seem at least interchangeable.

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