Investors underwhelmed with Mersana's early-stage data on lead candidate XMT-1522; shares down 18%

|About: Mersana Therapeutics (MRSN)|By:, SA News Editor

Thinly traded micro cap Mersana Therapeutics (MRSN -17.7%) slumps on modestly higher volume in apparent reaction to its announcement of updated data from a Phase 1 clinical trial evaluating lead antibody-drug conjugate (ADC) XMT-1522 in HER2-positive breast, non-small lung and gastric cancers. The results were presented at ASCO in Chicago.

Dose-limiting toxicity assessments have been completed across six dose levels (seventh is in process) but the maximum tolerated dose has not been reached. Advancement into Phase 2 development is on hold until the recommended dose is determined.

Of the 13 patients receiving 16 mg/m2 or greater, one experienced a partial response while 11 had stable cancer, implying a disease control rate of 75%.

The company will host a conference call and webcast today at 6:30 pm CT to review the data.