Breast Cancer Treatment: Positive Results in KEYTRUDA Trial

Triple-negative breast cancer (TNBC), a rare and aggressive form of cancer, occurs when one’s cancer is negative for progesterone receptors, estrogen receptors, and an excess of the HER2 protein. This means that many therapies that work for traditional breast cancer are unsuccessful in these cases. Now, Merck may offer another treatment option for TNBC, as it just announced positive results from a Phase 3 trial of KEYTRUDA.


Marketed as KEYTRUDA, pembrolizumab is an anti-PD-1 therapy that is intended for use in conjunction with chemotherapy before operations and continued use as a single-agent post-operation. Its job is to help the body find and fight cancer cells. It does so by stopping the interaction between PD-1 and its ligands, which then sets T lymphocytes in motion to fight cancer cells.

About the Study

Titled KEYNOTE-522, this Phase 3 trial evaluated KEYTRUDA as a treatment for TNBC in terms of its primary endpoints: event-free survival and pathological complete response (pCR). It is double-blind and randomized, with secondary endpoints such as overall survival, pCR rate using alternative definitions at the time of surgery, safety, event-free survival in participants with tumors expressing PD-L1, and patient-reported outcomes.

1.174 participants were enrolled and randomized 2:1. Some patients received four cycles of KEYTRUDA every three weeks, paclitaxel every week, and carboplatin every week or every three weeks, which was followed by four cycles of KEYTRUDA, cyclophosphamide, and doxorubicin or epirubicin every three weeks. After operations, these patients were administered nine cycles of KEYTRUDA every three weeks. The remaining patients were given a placebo rather than KEYTRUDA within the same treatment regimen.

After an interim analysis by Data Monitoring Committee (DMC), it was announced that the trial not only met its primary endpoint, but the therapy resulted in a clinically meaningful and statistically significant improvement in event-free survival. Additionally, no new safety signals were noted.

Looking Forward

Patients and medical professionals alike are very excited by this development, as it marks KEYTRUDA as the first immunotherapy to demonstrate positive results in TNBC patients in terms of event-free survival. Merck is very excited to work with regulatory agencies and other organizations to continue developing this treatment and offer it to patients.

About Breast Cancer

Breast cancer, as the name suggests, is a cancer that forms in the breast tissue. While it typically impacts females, males can also be affected. Medical professionals do not know why or how this cancer occurs; they only know that cells within the breast tissue begin to divide and multiply out of control until they form a tumor. They believe that both environmental and genetic factors play a role, and they have also identified risk factors: being female, a mutated BRCA1 or BRCA2 gene, obesity, having children at an older age, reaching menopause at an older age, starting your period at a younger age, never having been pregnant, drinking alcohol, postmenopausal therapy, and a history of breast cancer or related conditions. In terms of symptoms, patients typically notice a lump in the breast first. Other symptoms include redness, flaking, inverted nipples, changes in the size or shape of the breasts, peeling, scaling, crusting, dimpling, and pitting of the skin on the breasts. Treatment options are (double) mastectomy, immunotherapy, lumpectomy, the removal of numerous lymph nodes, hormone therapy, radiation, chemotherapy, and targeted therapy.

Looking at triple-negative breast cancer, it tests negative for progesterone receptors, estrogen receptors, and an excess of the HER2 protein. This form of cancer accounts for 10-20% of all cases. Unlike breast cancer, it will not respond to hormone therapy or any drugs that target the HER2 protein. It is also more aggressive than typical breast cancer and tends to be of a higher grade. Those with the BRCA1 mutation, younger people, and Black and Hispanic females live with the highest risk of this cancer. Learn more about it here.

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