What happened

Shares of Merus (MRUS -0.52%), a clinical-stage biopharmaceutical company, are soaring today in response to positive clinical trial results. Investors impressed with the company's latest presentation pushed the stock 39% higher as of 10:16 a.m. EDT on Thursday.

So what 

Today, Merus presented data from a clinical trial with MCLA-158 in patients with head and neck squamous cell cancer (HNSCC). The company also presented some pre-clinical data from its lead asset, zenocutuzumab, but all eyes were on MCLA-158.

Happy investor in front of an upward sloping chart.

Image source: Getty Images.

Among the first seven patients treated with MCLA-158 who also have at least eight weeks of follow-up observation, none of the targeted tumors got bigger. Three patients even exhibited a partial response.

Now what

MCLA-158 is a bispecific antibody that binds to cancer cells that express too much leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5) and epidermal growth factor receptor (EGFR). In theory, this should arrest tumor growth and recruit immune cells to attack those tumors at the same time.

So far, it looks like MCLA-158's unique approach is working as expected. When it comes to new cancer drug development, though, early looks can be deceiving. Impressive response rates that appear after the first handful of patients almost always become less impressive with time. Before risking money on Merus stock, it's probably a good idea to wait for a little more data.