Stereotactic Body Radiation Therapy Plus Pembrolizumab and Trametinib vs. Stereotactic Body Radiation Therapy Plus Gemcitabine for Locally Recurrent Pancreatic Cancer After Surgical Resection: an Open-label, Randomized, Controlled, Phase 2 Trial

Background and aim:

Pancreatic cancer is one of the most lethal malignancies and fourth leading cause of cancer death in both genders in US, where the mortality and incidence increase over the past decade with a lowest 5-year survival rate of 9% among all cancers. Although surgical resection is deemed to provide long-term disease control, only 20% patients were candidates for upfront surgery and unfortunately, even when adjuvant chemotherapy is prescribed, about 50% of patients will suffer local recurrence. Despite of emergence of immunotherapy as a new treatment paradigm, little improvement of outcomes has been found in pancreatic cancer. This may be ascribed to its inherent genetic mutations and immunosuppressive microenvironment. It has been demonstrated that radiotherapy could enhance the release and uptake of tumor-associated antigens, thus promoting antitumor T cell priming, and enhancing access to tumors due to effects both on the tumor vasculature and the chemokine milieu.

Despite of emergence of immune checkpoint inhibitors as a novel treatment paradigm for cancers, the results of investigations about the efficacy of immunotherapy alone for pancreatic cancer was disappointing. Due to enhanced immunogenicity of tumor irradiation, the underlying rationale of combination of radiotherapy and immunotherapy is that radiation can noninvasively prime the immune system against tumor cells, where antigen presentation and co-stimulation are facilitated, thus creating immune responses against previously hidden epitopes that are shared among distant metastases, while immune checkpoint inhibitors can reverse the immunosuppressive effects of the tumor microenvironment, thus facilitating antitumor immunity.

Although oncogenic mutations in KRAS are frequent in pancreatic cancer, KRAS proteins are difficult to be targeted due to high affinity for GTP and/or GDP. Therefore, efforts have been made to develop therapies targeting the major downstream effector pathways, which include the RAS-RAF-MEK-ERK and PI3K-PDPK1-AKT signaling pathways. MEK inhibitor trametinib alone or in combinations with chemotherapy or autophagy inhibitor hydroxychloroquine may probably have positive effects on tumor regression.

Regarding local recurrence after surgery, it was recommended that chemotherapy with optional radiotherapy may be the first-line treatment without addition of targeted therapy or immunotherapy owing to that no studies have investigated the efficacy of this regimen. Therefore, the aim of our study was to compare the outcomes between stereotactic body radiation therapy (SBRT) with pembrolizumab and trametinib and SBRT with gemcitabine for locally recurrent pancreatic cancer after surgical resection.