Circulating tumor cell (CTC) number measured with the CellSearch assay is prognostic for survival in metastatic castration-resistant prostate cancer before and after therapy. Using a standard operating protocol for sample collection, processing, and analysis, we compared detection rates of CellSearch performed using US Food and Drug Administration–cleared methodology with a second positive selection assay, AdnaTest, and a nonselection polymerase chain reaction (PCR)–based (direct detection PCR [DDPCR]) assay in 55 blood samples from 47 men with progressive metastatic castration-resistant prostate cancer. AdnaTest requires processing within 4 hours of the draw and detects KLK3, PSMA, and EGFR transcripts in cells captured on magnetic beads. The DDPCR assay can be processed up to 7 days after a draw and detects KLK2, KLK3, HOXB13, GRHL2, and FOXA1 genes. AdnaTest and DDPCR were considered positive if at least 1 transcript was detected. AdnaTest detected CTCs in 34 samples (62%; 95% confidence interval [CI], 48%–75%), of which 23 (68%) had unfavorable CTC counts by CellSearch. A positive DDPCR result was seen in 38 cases (69%; 95% CI, 55%–81%), including 24 (63%) with unfavorable CellSearch CTC counts. CellSearch found unfavorable CTC counts in 25 samples (45%; 95% CI, 33%–58%). Sensitivities were similar between the AdnaTest and DDPCR assays, and both were more sensitive than CellSearch. Concordance probability estimates (possible values, 0.5–1.0) associating the biomarker result with survival were similar: 0.77 (SE, 0.07) for AdnaTest, 0.72 (SE, 0.08) for DDPCR, and 0.76 (SE, 0.06) for CellSearch. Overall detection rates between the AdnaTest and DDPCR assays were similar, and both were superior to CellSearch. The DDPCR assay required the lowest blood volume, least on-site processing, and longest stability for batch processing.

Purpose:Reliable molecular diagnostic tools are still unavailable for making informed treatment decisions and monitoring the response in castration resistant prostate cancer (CRPC) patients. In thi...

5029 Background: STEAP1 is overexpressed in mCRPC and is an ADC target. STEAP1 expression in tissue assayed by IHC, protein and mRNA expression levels in circulating tumor cells (CTC) and by 89Zr-labeled anti-STEAP1 antibody uptake by iPET. Methods: Patients (pts) with progressive mCRPC received doses of the ADC ranging from 0.3 to 2.8 mg/kg once every three weeks. Antitumor activity was assessed by PSA declines, time on study and changes in CTC number (CellSearch). STEAP1 expression in tumor tissue by a validated IHC assay was used as reference biomarker on a scale of 0 (not detected) to 3+ (highest expression). Protein and mRNA expression in CTCs was explored by FACS and RT-PCR, and standardized uptake values (SUV) of 89Zr-labeled anti-STEAP1 antibody by iPET. Results: At doses of ≥ 2 mg/kg, a ≥ 50% PSA decline was observed in 22% (10/45, 11-37%), and CTC conversions from unfavorable (> 5 cells) to favorable (4 or fewer/7.5 ml of blood) in 55% (11/20, 32-77%) of cases. CTC showed a readily detectable ST...

45 Background: To estimate the association between molecular biomarkers and outcomes, robust assays are needed before qualification in prospective trials. Although tumor specific transcripts detected in blood by PCR have been associated with outcome, an analytically validated PCR platform enabling detection of CTC-associated transcripts in clinical settings remains to be identified. Here we explore detecting a panel of prostate specific transcripts in conjunction with conventional markers in CRPC. Methods: Blood was collected from 97 patients with progressive CRPC in PAXgene tubes (2.5 ml) for total RNA extraction. Five genes expressed in prostate but not in nucleated blood cells were analyzed by primer-specific RT-PCR. Fluidigm Dynamic Array platform was analytically validated for KLK3, KLK2, HOXB13, GHRL2 and FOXA1 assays. Each PCR-reaction was run in 6 replicates, detection thresholds for each gene were chosen by ROC analysis of an independent set of 56 CRPC patients versus 51 healthy volunteers, and results were reported as transcripts present or absent. CellSearch reported CTC number/7.5 ml of blood drawn into CellSave tube. Results: Prostate specific transcripts for KLK3, KLK2, HOXB13, GHRL2 and FOXA1were detected in 50 (52%), 39 (40%), 53 (55%), 28 (29%) and 47 (48%) of patients, respectively.Two or more genes were detected in 53/97 patients (55%, 95% CI 45-65%) of patients with progressive CRPC studied with a median survival time of 17 months (95% CI: 13.8, 23.5). 40/45 CRPC-patients with ≥5 CTC and 13/52 CRPC patients with

Background: Fluoroquinolone prophylaxis during autologous stem cell transplantation (aSCT) reduces the risk of fever but raises the risk of bloodstream infection (BSI) with fluoroquinolone-resistant Enterobacterales (FRE). We performed a prospective cohort study to detect the presence and potential gain or loss of colonic FRE colonization using serial sampling before and after aSCT in a uniform population of patients with a diagnosis of multiple myeloma. Methods: Eligible subjects underwent aSCT after conditioning with dose-intense melphalan, 200 mg/m². Peri-anal swabs were obtained before aSCT, upon hospital discharge, and 12–16 weeks after transplantation. Samples were cultured in tryptic soy broth supplemented with either ciprofloxacin or ceftriaxone with subsequent plating onto selective chromogenic agar designed to facilitate recovery and differentiation of Enterobacterales. Results: FRE colonization on pre-transplant sampling was detected for 23 of 117 subjects (19.7%) and 29 of 98 (29.6%) subjects at hospital discharge after a course of fluoroquinolone (116/117 subjects) prophylaxis (p < 0.001) and 28 of 92 (30.4%) subjects at 12–16 weeks. Including all three sampling time points, 48 of 117 subjects (41.0%) tested positive for FRE colonization. In total, 58 of the 90 FRE isolates (64.4%) from 48 subjects expressed extended-spectrum beta-lactamase (ESBL). Three FRE-colonized subjects developed FRE BSI. Bloodstream isolates for two subjects were identical to the organisms identified on pre-transplant sampling. Conclusions: We hypothesize that fluoroquinolone prophylaxis of subjects with undetected low levels of FRE colonization allows the expansion of the FRE population, placing subjects at risk of BSI with fluoroquinolone-resistant (and ESBL-expressing) Enterobacterales. Pre-transplant testing for FRE colonization permits patient-specific design of prophylactic and empiric antibiotic regimens.