What happened

Shares of Mersana Therapeutics (NASDAQ:MRSN) were skyrocketing 32.7% higher as of 11:07 a.m. EDT on Wednesday. The big jump came after the biotech announced positive interim results from the expansion portion of an early-stage study evaluating antibody-drug conjugate (ADC) XMT-1536 in treating patients with ovarian cancer.

So what

Investors liked the numbers that Mersana reported from its early-stage study. Patients receiving XMT-1536 achieved a 35% objective response rate (tumor reduction by a pre-specified amount). Ten percent of patients with ovarian cancer experienced complete remission after taking XMT-1536. The disease control rate (proportion of patients with complete response, partial response, or stable disease) was 80%.

Red line pointing up with a rocket flying over it

Image source: Getty Images.

In addition, XMT-1536 appeared to have a pretty good safety profile. Mersana Therapeutics CEO Anna Protopapas said the drug was "generally well tolerated, without the dose-limiting toxicities of other ADC platforms such as severe neutropenia, neuropathy and ocular toxicity."

All of these results were also really early. The interim results reflected data from only 20 patients with ovarian cancer. Mersana didn't report any information from the other 14 patients in the study, seven of whom have ovarian cancer and seven of whom have non-small cell lung adenocarcinoma.

Now what

Mersana plans to present the interim data at the American Society of Clinical Oncology (ASCO) 2020 virtual scientific program this Friday. An even bigger catalyst for the biotech stock could be on the way: Mersana anticipates reporting more data from the early-stage study of XMT-1536 in the second half of 2020.