Clinical trials (or clinical studies) are reseach studies involving human participants carefully designed to study whether new drugs or treatments are safe and effective.

XCaliber is a clinical trial evaluating the safety and efficacy of XMT-2056 in adult patients with advanced/recurrent solid tumors that express HER2. The trial consists of 2 parts:

• Part 1 dose escalation will evaluate the safety and preliminary efficacy of XMT-2056 in cancer patients receiving multiple dose levels. Patients will be dosed in different groups, some receiving lower doses and some receiving higher doses. This will help identify the highest dose that is safe to use. The determined dose will be used for Part 2.

• Part 2 dose expansion will evaluate the safety and preliminary efficacy of XMT-2056 in a larger number of cancer patients.

XMT-2056 is an antibody-drug-conjugate (ADC) that is designed to activate your immune system to fight cancer. XMT-2056 is administered as an intravenous infusion.

XMT-2056 is an investigational treatment that is currently not approved by the FDA or any other regulatory authority for the treatment of cancer.

Patients that meet the following basic criteria may be candidates for the trial:

• Patient has HER2-expressing solid tumor.
• Patient has recurrent or metastatic disease following progression on standard-of-care therapy.
• Pateint, male or female, must be at least 18 years old.
• Additional eligibility criteria will be determined based on factors such as prior treatments, overall health status, laboratory test results, and other protocol-defined requirements. Only a trial investigator can determine if a patient is eligible to take part in a clinical trial; however, this information may be useful in starting a conversation with your doctor.

If eligible, additional information on the trial and your responsibilities will be provided by your doctor.

Mersana Therapeutics is the sponsor of the study. Headquartered in Cambridge, MA, Mersana Therapeutics is a clinical-stage biopharmaceutical company focused on the development of novel ADCs and driven by the knowledge that patients are waiting for new treatment options.

If you do not see a location near you, your primary care physician or oncologist may be able to refer you to another clinical trial site.

You can ask questions of the trial team at any time before, during, and after the trial. Before agreeing to participate, make sure you understand the responsibilities of clinical trial participants. If you have any concerns, you should feel comfortable discussing them with a member of the trial staff at any time.

Your participation is this trial is voluntary. You can stop participating in the trial at any time, and for whatever reason, with no change to the medical care you are otherwise entitled to receive. This will not affect your relationship with your regular treating doctor.

If you have additional questions on the trial and/or your eligibility, please contact one of the trial sites, discuss the trial with your doctor or send an email to Medicalinformation@Mersana.com.