WES reads were aligned against the GrCH37d5 genome using the Sanger cppmap workflow ( ) with realignment around indels and base recalibration performed using the Open Genomics GATK cocleaning workflow ( ). 23 DNA-repair genes examined included well-described markers (BRCA2, ATM, FANCA, CHEK2, BRCA1, PALB2, HDAC2, RAD51, MLH3, ERCC3, MRE11, NBN) as well as markers that could potentially have clinical relevance (BARD1, BRIP1, CDK12, RAD51B, RAD51C, RAD51D, RAD54L). MSI was assessed by PCR of BAT-25, BAT-26, NR-21, NR-24, MONO-27 for all patients, with orthogonal MSI analysis of almost 3000 different markers using microsatellite instability detection by next generation sequencing (mSINGS). 22 All responders underwent WES regardless of tumor content.
21 Two patients were tested using the Personal Genome Diagnostics panel (Baltimore, Maryland, USA), which tested 203 genes for the same features as the GeneTrails test. Exploratory endpoints were the fraction of PD-L1 expressing tumor cells and the number of genetic mutations per biopsy, including testing for microsatellite instability (MSI) and mutations associated with DNA-repair defects.Īll baseline tumor biopsies underwent analysis by whole exome sequencing (WES) for samples containing ≥10% tumor or by genotyping using the Knight Diagnostic Laboratory’s GeneTrails Solid Tumor Panel of 124 genes frequently altered in cancer, which assessed single nucleotide variations, multinucleotide variations, indels, and copy number variations if the sample contained <10% tumor.
Secondary endpoints were PSA progression-free survival (PFS), objective response, radiographic PFS per RECIST V.1.1, time to next treatment and overall survival. The primary endpoint of the study was a confirmed serum PSA decrease ≥50% at any time on treatment. Here we present the results of a phase II study examining the antitumor effect of pembrolizumab added to enzalutamide in men with mCRPC whose cancer is progressing on enzalutamide alone. Additionally, we previously reported a profound response to immunotherapy (anti-CTLA-4) in a man with mCRPC on enzalutamide with biochemical progression. Since enzalutamide is associated with increased expression of PD-L1 16 and enzalutamide augments castration, we hypothesized that enzalutamide would be a strong partner to PD-1 inhibitors. 17 However, a recent analysis revealed that one-third of mCRPC biopsies exhibit PD-1 staining 18 suggesting that strategies to enhance CD8+ T cell function and decrease inhibitory signals in the tumor may underlie the success of immunotherapies for prostate cancer. 16 Primary prostate cancer tumors are considered ‘cold tumors’ poorly infiltrated with T cells, and there is a general lack of PD-L1 expression on prostate cancer cells. Studies showed that PD-L1, a ligand for PD-1, was upregulated on dendritic cells in men with mCRPC either progressing on or refractory to enzalutamide. 14 Combinations of PD-1 inhibition with CTLA-4 and the poly-ADP ribose polymerase (PARP) inhibitor olaparib have also demonstrated activity. 13 In the second study, all patients had received docetaxel, but there was no clear difference in response rate between those with PD-L1 positive (n=131) staining versus negative staining (n=67). One enrolled only PD-L1 positive mCRPC (n=23), most of which had received prior docetaxel (91%), and a 17.4% durable response rate was observed. 10–12 Two recent studies examined single-agent pembrolizumab for programmed death ligand 1 (PD-L1) positive and PD-L1 negative mCRPC. Two phase III studies of the anti-Cytotoxic T Lymphocyte-Associated Protein-4 (CTLA-4) antibody ipilimumab failed to meet their primary endpoint of improved overall survival, and early studies of programmed cell death protein-1 (PD-1) inhibitors showed no objective radiographic responses in men with mCRPC. To date, immune checkpoint inhibitors used as monotherapy in mCRPC have shown mixed activity. Management of mCRPC after enzalutamide and/or abiraterone is a particularly challenging clinical problem. 2–9 There are few data to guide sequencing of these agents and no data supporting routine use of combination therapies.
1 Current therapies that extend survival for mCRPC include second-generation androgen receptor antagonists (enzalutamide), inhibitors of androgen synthesis (abiraterone), chemotherapy (docetaxel, cabazitaxel), a cellular vaccine (sipuleucel-T) and a radiopharmaceutical (radium-223). Despite advancements in the management of metastatic castration-resistant prostate cancer (mCRPC), prostate cancer remains the second most common cause of cancer death in US men.