Study of Patritumab Deruxtecan Plus Pembrolizumab With Other Anticancer Agents in Participants With High-Risk Early-Stage Triple-Negative or Hormone Receptor-Low Positive/HER-2 Negative Breast Cancer (MK-1022-010, HERTHENA-Breast-03)

BIOLOGICAL

Patritumab deruxtecan

Administered via IV infusion as neoadjuvant treatment

BIOLOGICAL

Pembrolizumab

Administered via IV infusion as neoadjuvant treatment in Part 1 and via IV infusion as neoadjuvant and adjuvant treatment in Part 2

DRUG

Paclitaxel

Administered via IV infusion as neoadjuvant treatment

DRUG

Carboplatin

Administered via IV infusion as neoadjuvant treatment

DRUG

Doxorubicin hydrochloride

Administered via IV infusion as neoadjuvant treatment in Arm C and an option for adjuvant treatment for participants with residual disease in Arms A and B in Part 2

DRUG

Epirubicin hydrochloride

Administered via IV infusion as neoadjuvant treatment in Arm C and an option for adjuvant treatment for participants with residual disease in Arms A and B in Part 2

DRUG

Cyclophosphamide

Administered via IV infusion as neoadjuvant treatment in Arm C and an option for adjuvant treatment for participants with residual disease in Arms A and B in Part 2

DRUG

Capecitabine

Administered via oral tablets as an option for adjuvant treatment for participants with residual disease in Part 2

DRUG

Olaparib

Administered via oral tablets as an option for adjuvant treatment for participants with germline BRCA mutations and residual disease in Part 2

Part 1: Number of Participants Experiencing an Adverse Event (AE)

Time frame: Up to ~43 weeks

An AE is defined as any unfavorable and unintended sign, symptom, disease, or worsening of preexisting condition temporally associated with study treatment and irrespective of causality to study treatment. The number of participants who experience an AE will be presented for Part 1.

Part 1: Number of Participants Who Experience One or More Dose-Limiting Toxicities (DLTs)

Time frame: Up to 21 days

A DLT is defined by the National Cancer Institute Common Terminology for Adverse Events (NCI CTCAE) Version 5.0, assessed by investigator as drug-related: Grade (gr) 3 or 4 nonhematologic toxicity (with exceptions); gr 3 or gr 4 laboratory values (with exceptions); gr 3 or 4 febrile neutropenia; prolonged delay (\>2 weeks) in initiating Cycle 2 (cycle length = 3 weeks) due to intervention-related toxicity; any intervention-related toxicity that causes the participant to discontinue intervention during Cycle 1; interstitial lung disease as per investigator; any other gr ≥3 pulmonary toxicity; or gr 5 toxicity.

Part 1: Number of Participants who Discontinued Study Treatment Due to an AE

Time frame: Up to ~30 weeks

An AE is defined as any unfavorable and unintended sign, symptom, disease, or worsening of preexisting condition temporally associated with study treatment and irrespective of causality to study treatment. The number of participants who discontinued study treatment due to an AE will be presented for Part 1.

Part 2: Pathological Complete Response (pCR) Rate Using the Definition of ypT0/Tis ypN0

Time frame: Up to ~30 weeks

pCR (ypT0/Tis ypN0) is defined as the absence of residual invasive cancer on hematoxylin and eosin evaluation of the complete resected breast specimen and all sampled regional lymph nodes after completion of neoadjuvant systemic therapy at the time of definitive surgery.

Part 2: Number of Participants Experiencing an AE

Time frame: Up to ~103 weeks

An AE is defined as any unfavorable and unintended sign, symptom, disease, or worsening of preexisting condition temporally associated with study treatment and irrespective of causality to study treatment. The number of participants who experience an AE will be presented for Part 2.

Part 2: Number of Participants who Discontinued Study Treatment Due to an AE

Time frame: Up to ~90 weeks

An AE is defined as any unfavorable and unintended sign, symptom, disease, or worsening of preexisting condition temporally associated with study treatment and irrespective of causality to study treatment. The number of participants who discontinued study treatment due to an AE will be presented for Part 2.

What is a clinical trial?

A clinical trial is a research study that tests new medical treatments, drugs, devices, or procedures to determine their safety and effectiveness. Trials are carefully designed and monitored to protect participants while advancing medical knowledge.

Is it safe to participate?

Clinical trials follow strict safety guidelines and ethical standards. Trials must be reviewed and approved, and participants are closely monitored by medical professionals throughout the study. You can withdraw at any time if you choose.

Will I be compensated?

Many clinical trials offer compensation for your time, travel expenses, and inconvenience. The specific compensation varies by study and will be discussed during the screening process. All study-related medical care is typically provided at no cost to participants.

Will I receive a placebo instead of treatment?

When effective treatment exists, participants typically receive either the standard treatment plus the study intervention, or the standard treatment plus placebo. You would not be denied effective care. Placebos are primarily used when no proven treatment is available, or in addition to standard care. Your trial consent form will clearly explain what treatments you may receive.

Can I leave a trial if I change my mind?

Absolutely. Participation in clinical trials is completely voluntary. You have the right to withdraw from the study at any time, for any reason, without penalty or loss of benefits to which you are otherwise entitled.

How long does a clinical trial last?

Trial duration varies widely depending on the study design and purpose. Some trials last just a few weeks, while others may continue for months or years. The study coordinator will provide specific timeline information during your screening call.