Pembrolizumab for a patient with metastatic castration-resistant prostate cancer with microsatellite instability-high

The Role of Histology-Agnostic Drugs in the Treatment of Metastatic Castration-Resistant Prostate Cancer

Precision medicine has opened up a new era in the development of anti-cancer agents that is focused on identifying biomarkers predictive of treatment response regardless of tumor histology. Since 2017, the Food and Drug Administration has approved six drugs with histology-agnostic indications: pembrolizumab (both for tumors with the mismatch-repair deficiency (dMMR)/high microsatellite instability (MSI-H) phenotype and for those with the high tumor mutational burden (TMB-H) phenotype), dostarlimab (for dMMR tumors), larotrectinib and entrectinib (for tumors harboring neurotrophic tyrosine receptor kinase (NTRK) fusions), and the combination of dabrafenib plus trametinib (for BRAF V600E-mutated tumors). The genomic alterations targeted by these antineoplastic agents are rare in metastatic castration-resistant prostate cancer (mCRPC). Furthermore, only a small number of mCRPC patients were enrolled in the clinical trials that led to the approval of the above-mentioned drugs. Therefore, we critically reviewed the literature on the efficacy of histology-agnostic drugs in mCRPC patients. Although the available evidence derives from retrospective studies and case reports, our results confirmed the efficacy of pembrolizumab in dMMR/MSI-H mCRPC. In contrast, few data are available for dostarlimab, larotrectinib, entrectinib, and dabrafenib-trametinib in this subset of patients. Large, multi-institutional registries aimed at collecting real-world data are needed to better comprehend the role of tissue-agnostic drugs in mCRPC patients.

A case of microsatellite instability-high clinically advanced castration-resistant prostate cancer showing a remarkable response to pembrolizumab sustained over at least 18 months

Defective DNA mismatch repair genes can lead to microsatellite instability (MSI)-high status in prostate cancer (PC). Accumulation of replication errors in DNA leads to the production of abundant neoantigens, which could be targets for immune checkpoint inhibitors (CPIs). However, the incidence of MSI-high PC is low, and not all patients show a satisfactory therapeutic response to CPIs. Here, we present the case of a patient with MSI-high castration-resistant PC who showed a remarkable and durable response to pembrolizumab. The patient was resistant to abiraterone, docetaxel, and cabazitaxel and was suffering from multiple tumor-associated or treatment-related complications, such as urinary tract infection, infective endocarditis, and uncontrollable prostatic hemorrhage. Soon after the start of pembrolizumab therapy, the patient showed a dramatic decrease in prostate-specific antigen from 35.67 ng/mL to an undetectable level and a remarkable reduction in the size of a massive prostate mass and lymph node metastases, with an absence of treatment-related complications. Specimens from the transurethral resection of prostate cancer during cabazitaxel treatment for control of prostate bleeding and also that from the prostate biopsy at initial diagnosis revealed MSI-high status. Immunohistochemistry showed loss of MSH2 and MSH6, and whole-exome sequencing revealed an approximate tumor mutation burden of 61 mutations/Mb as well as biallelic loss of MSH2. Pembrolizumab could show a significant effect even in a heavily treated patient with MSI-high advanced PC. Accumulation of detailed clinical and genomic information of cases of MSI-high PC treated with pembrolizumab is necessary for optimal patient selection.

Recent Advances in Medical Therapy for Urological Cancers

The mainstay of medical treatment has been tyrosine kinase inhibitors (TKIs) for renal cell cancer (RCC), cytotoxic chemotherapy for urothelial cancer (UC), and androgen deprivation therapy for prostate cancer. These therapeutic modalities still play important roles in these malignancies. However, immune checkpoint inhibitors (ICIs) that target PD-1/PD-L1 or CTLA-4 are being rapidly introduced for the treatment of metastatic urological cancers, just as they have been for other malignancies. Currently, the paradigm of medical treatment for patients with metastatic urological cancer is dramatically changing. Accordingly, we need to organize and summarize the new therapeutic tools, which include immune checkpoint inhibitors, poly (ADP-ribose) polymerase (PARP) inhibitors, and antibody-drug conjugates (ADCs). This review provides an overview of agents and regimens that have just launched or will be launched in the near future in Japan. Based on the promising anti-tumor efficacy and manageable safety profiles being demonstrated in clinical trials, these new agents and therapies are expected to be rapidly introduced in Japanese clinical practice. Additionally, the newly designed ADC, enfortumab vedotin, which comprises a fully human monoclonal antibody conjugated to an anti-cancerous agent via a protease-cleavable linker, has just been launched in Japan. In order to provide the optimal treatment for our patients, we need to completely understand these new therapeutic tools.

Efficacy, Prognostic Factors, and Safety Profile of Enzalutamide for Non-metastatic and Metastatic Castration-Resistant Prostate Cancer: A Retrospective Single-Center Analysis in Japan

BACKGROUND

Enzalutamide is a novel, non-steroidal anti-androgen that has demonstrated excellent anti-tumor activity for both non-metastatic and metastatic castration-resistant prostate cancer (nmCRPC and mCRPC) patients, and that is being rapidly introduced into clinical practice in Japan.

OBJECTIVE

We retrospectively investigated the treatment efficacy, safety profile, and prognostic factors of enzalutamide over a relatively long observation period in Japanese patients with nmCRPC and mCRPC.

PATIENTS AND METHODS

The medical records of 184 consecutive Japanese patients with nmCRPC and mCRPC who started enzalutamide treatment in our institution between January 2012 and April 2018 were reviewed. Efficacy and safety profiles were assessed and statistically analyzed.

RESULTS

Among these 184 patients, 44 (23.9%) nmCRPC patients, 89 (48.4%) docetaxel-naïve mCRPC patients, and 51 docetaxel-pretreated (27.7%) mCRPC patients underwent enzalutamide therapy. The median prostate-specific antigen progression-free survival (PSA-PFS) and overall survival (OS) periods for nmCRPC patients were 39.2 months and not reached; those for docetaxel-naïve mCRPC patients were 16.5 months and 59.8 months; and those for docetaxel-pretreated mCRPC patients were 7.0 months and 30.4 months, respectively. Multivariate analysis identified performance status ≥ 2, PSA > 8.89 ng/mL (median value), hemoglobin < lower limit of normal range, neutrophil to lymphocyte ratio > 3.0, and 4-week PSA decline < 50% as the predictive factors for shorter OS. Our respective prognostic models using these factors successfully demonstrated distinctly separated survival curves (p < 0.001). In addition, among these patients, 30 (16.3%) experienced adverse events and 16 (8.7%) experienced adverse events resulting in the discontinuation of therapy. Fatigue (14%) and appetite loss (7%) were the most common such events.

CONCLUSIONS

Both the survival period and risk factors were extracted from a relatively long-term observation period. Since enzalutamide was approved for administration to patients with castration-sensitive prostate cancer earlier this year (2020), we believe that the data presented here will be useful for both physicians and patients in clinical practice.