Background Pembrolizumab is approved for patients with metastatic, microsatellite instability (MSI)‐high or mismatch repair‐deficient (dMMR) solid tumors. However, very few men with prostate cancer were included in these initial studies. Methods We performed a single institution retrospective review of men with metastatic castrate‐resistant prostate cancer (mCRPC) who were treated with pembrolizumab. The primary objective was to describe the clinical efficacy of pembrolizumab associated with patient and genomic characteristics. Results We identified 48 men who received ≥1 cycle of pembrolizumab for mCRPC. Of these, 94% (45/48) had ≥3 prior lines of therapy for mCRPC. Somatic tumor sequencing was available in 18/48 men (38%). We found that 17% (8/48) had a ≥50% confirmed PSA decline with pembrolizumab, and 8% (4/48) had a ≥90% PSA decline with durations of response ranging from 3.1 to 16.3 months. Two of these four men had mutations in LRP1b , one of whom also had MSH2 loss and was MSI‐H and TMB‐high. Despite prior progression on enzalutamide, 48% (23/48) of men were treated with concurrent enzalutamide. The median PSA progression‐free‐survival was 1.8 months (range 0.4‐13.7 months), with 31% of patients remaining on pembrolizumab therapy and 54% of men remain alive with a median follow‐up of 7.1 months. Conclusions In a heavily pretreated population of men with mCRPC, pembrolizumab was associated with a ≥50% PSA decline in 17% (8/48) of men, including a dramatic ≥90% PSA response in 8% (4/48), two of whom harbored pathogenic LRP1b mutations suggesting that LRP1b mutations may enrich for PD‐1 inhibitor responsiveness in prostate cancer.

Immune checkpoint blockers have revolutionized cancer treatment in recent years. These agents are now approved for the treatment of several malignancies, including melanoma, squamous and non-squamous non-small cell lung cancer, renal cell carcinoma, urothelial carcinoma, and head and neck squamous cell carcinoma. Studies have demonstrated the significant impact of immunotherapy versus standard of care on patient outcomes, including durable response and extended survival. The use of immunotherapy-based combination therapy has been shown to further extend duration of response and survival. Immunotherapies function through modulation of the immune system, which can lead to immune-mediated adverse events (imAEs). These include a range of dermatologic, gastrointestinal, endocrine, and hepatic toxicities, as well as other less common inflammatory events. ImAEs are typically low grade and manageable when identified early and treated with appropriate measures. Identifying the right patient for the right therapy will become more important as new immunotherapies and immunotherapy-based combinations are approved and costs of cancer care continue to rise.

No abstract

Aminopterin can be safely incorporated in multiagent therapy for patients with ALL, in place of systemic methotrexate, without causing excessive toxicity. These results support a larger trial comparing the efficacy and toxicity of aminopterin and methotrexate in therapy for patients with ALL.

6547 Background: Although medication errors comprise 10–25% of all medical errors, little is known concerning the occurrence or types of medication errors occurring while treating patients on a clinical trial. Therefore, we retrospectively reviewed the medication errors reported in patients enrolled on clinical trials at our center. Methods: As part of a multidisciplinary continuous quality improvement project, from January 2003 through December 2006, we collected voluntary reports of medication errors in adult and pediatric patients on clinical trials involving both oral and intravenous chemotherapy. All reports were classified prospectively regarding clinical trial involvement, severity category (A to I) per the National Coordination Council on Medical Error Reporting and Prevention, type, cause, and where in the medication use process the error occurred. Results: There were 163 reports involving patients treated on clinical trials. The most common errors were those corrected prior to reaching the patient in 68% of events (Category A&B), while 31% reached the patient but did not result in harm (Category C&D), with 1% resulting in temporary patient harm (Category E&F). The most common type of errors were prescribing (66%), improper dose (42%), and omission errors (9%). Not following an institutional procedure or the protocol was the primary cause for these errors (39%), followed by the written order (30%), and poor communication involving both the healthcare team and the patient (26%). The processes where the errors initiated were in prescribing 47%, administration 10%, dispensing 6%, and monitoring 5%. Conclusion: Medication errors do occur in clinical trials, however the majority of these are corrected prior to reaching the patient or do not result in harm. Not following an institutional procedure or the protocol was the most common cause of error. This is most likely due to the protocol procedures differing from existing standards of care. Protocol-specific education through the Centralized Education and Training Service, a shared resource within our cancer center, addresses this issue enhancing the quality and safety of clinical trials through the education and training of healthcare professionals. No significant financial relationships to disclose.