SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. The American Cancer Society estimates that in the US, approximately 310,720 new cases of female breast cancer will be diagnosed in 2024, and about 42,250 individuals will die of the disease, largely due to metastatic recurrence.
Triple Negative Breast Cancer (TNBC) is a heterogeneous, molecularly diverse group of breast cancers and are ER (Estrogen Receptor), PR (Progesterone Receptor) and HER2 (Human Epidermal Growth Factor Receptor-2) negative. TNBC accounts for 15-20% of invasive breast cancers, with a higher incidence noted in young patients. It is usually aggressive, and tumors tend to be high grade and patients with TNBC are at a higher risk of both local and distant recurrence. Those with metastatic disease have one of the worst prognoses of all cancers with a median Overall Survival (OS) of 13 months. The majority of patients with TNBC who develop metastatic disease do so within the first 3 years after diagnosis, whereas those without recurrence during this period of time have survival rates similar to those with ER-positive breast cancers.
Neoadjuvant chemotherapy is the preferred treatment approach in this group of patients and can potentially increase the likelihood of tumor resectability and breast conservation. Further, a pathological Complete Response (pCR) after neoadjuvant chemotherapy can result in a longer Event-Free Survival and Overall Survival. Pathological Complete Response is therefore used as an end point for clinical testing of neoadjuvant treatment in patients with early triple-negative breast cancer.
KEYTRUDA® (Pembrolizumab) is a fully humanized, Immunoglobulin G4, anti-PD-1, monoclonal antibody, that binds to the PD-1 receptor and blocks its interaction with ligands PD-L1 and PD-L2. It thereby reverses the PD-1 pathway-mediated inhibition of the immune response, and unleashes the tumor-specific effector T cells. The rationale for combining chemotherapy with immunotherapy is that cytotoxic chemotherapy releases tumor-specific antigens, and immune checkpoint inhibitors such as Pembrolizumab when given along with chemotherapy can enhance endogenous anticancer immunity. Single agent Pembrolizumab in metastatic TNBC demonstrated durable antitumor activity in several studies, with Objective Response Rates (ORRs) ranging from 10-21% and improved clinical responses in patients with higher PD-L1 expression. When given along with chemotherapy as a neoadjuvant treatment for patients with high-risk, early-stage TNBC, Pembrolizumab combination achieved pathological Complete Response rate of 65%, regardless of PD-L1 expression.
KEYNOTE-522 trial is a multicenter, randomized, double-blind, placebo-controlled Phase III trial, conducted to evaluate the efficacy and safety of neoadjuvant Pembrolizumab plus chemotherapy as compared with neoadjuvant placebo plus chemotherapy, followed by adjuvant Pembrolizumab or placebo in patients with early stage, high-risk, Triple Negative Breast Cancer. In this study, total of 1174 patients (N=1174) regardless of tumor PD-L1 expression, were randomly assigned 2:1 to receive Pembrolizumab plus chemotherapy (N=784) or placebo plus chemotherapy (N=390). Eligible patients had newly diagnosed, previously untreated, Triple Negative Breast Cancer, with tumor size more than 1 cm but 2 cm or less in diameter with nodal involvement, or tumor size more than 2 cm in diameter regardless of nodal involvement. Patients in the neoadjuvant phase received four cycles of Pembrolizumab 200 mg IV or placebo once every 3 weeks plus Paclitaxel 80 mg/m2 once weekly plus Carboplatin AUC 5 IV once every 3 weeks or Carboplatin AUC 1.5 IV once weekly in the first 12 weeks (first neoadjuvant treatment), followed by four cycles of Pembrolizumab or placebo along with Doxorubicin 60 mg/m2 IV or Epirubicin 90 mg/m2 IV plus Cyclophosphamide 600 mg/m2 IV once every 3 weeks in the subsequent 12 weeks (second neoadjuvant treatment). Patients then underwent definitive surgery (breast conservation or mastectomy with sentinel lymph-node evaluation or axillary dissection) 3-6 weeks after the last cycle of the neoadjuvant phase. In the adjuvant phase, patients received radiation therapy as indicated and Pembrolizumab or placebo once every 3 weeks for up to nine cycles. Adjuvant Capecitabine was not allowed. The median age was 49 yrs, 64% were white, 56% were premenopausal, and overall 75% had Stage II disease and 25% had Stage III disease. Both treatment groups were well balanced with regard to age, ECOG performance status, PD-L1-positivity, tumor size and nodal involvement. The Primary end points were a pathological Complete Response (pCR) at the time of definitive surgery and Event-Free Survival (EFS) in the intent-to-treat population. Pathological Complete Response was defined as absence of invasive cancer in the breast and lymph nodes (ypT0/Tis ypN0), and was assessed by the blinded local pathologist at the time of definitive surgery. EFS was defined as the time from randomization to the first occurrence of progression of disease that precludes definitive surgery, local or distant recurrence, second primary malignancy, or death due to any cause.
The pathological Complete Response rate was 63% in the Pembrolizumab plus chemotherapy group and 55.6% in the placebo plus chemotherapy group, and this difference were statistically significant. The EFS after median follow up of 63.1 months showed a 5-year EFS rate of 81.3% with Pembrolizumab plus chemotherapy and 72.3% with placebo plus chemotherapy (HR=0.63). The median EFS had not been reached in either group. The EFS benefit appeared consistent across subgroups, including those assessed by nodal status, disease stage, PD-L1 expression, menopausal status and Carboplatin schedule. A prespecified, exploratory analysis showed higher 5-year EFS rates with Pembrolizumab among patients who achieved pathologic Complete Response (92.2% versus 88.2%) and among those who did not achieve pathologic Complete Response (62.6% versus 52.3%).
It was concluded that the addition of Pembrolizumab with neoadjuvant chemotherapy followed by Pembrolizumab monotherapy in the adjuvant setting resulted in a durable Event Free Survival benefit, for patients with early stage Triple Negative Breast Cancer, and this benefit was noted across key subgroups, as well as among patients who did or did not achieve pathologic Complete Response.
Neoadjuvant pembrolizumab or placebo plus chemotherapy followed by adjuvant pembrolizumab or placebo for early-stage triple-negative breast cancer: updated event-free survival results from the phase 3 KEYNOTE-522 study. Schmid P, Cortés J, Dent R, et al. Presented at the 2023 San Antonio Breast Cancer Symposium; December 5-9, 2023; San Antonio, TX; abstract LBO1-01.
