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Supplementary data - Table S1. Incidence of all adverse events occurring in {greater than or equal to}15% of patients as well as grade 3 to 5 adverse events* Figure S1. Study schematic. Figure S2. Time-to-PSA progression* from testosterone recovery to {greater than or equal to}175 ng/dL. Figure S3. Time-to-testosterone recovery. Figure S4. Time-to-next anti-cancer intervention in both arms. Figure S5. Comparison of humoral antigen spread at week 2 between STAND versus IMPACT and STAMP. Figure S6. Sipuleucel-T parameters: (A) TNC count, (B) APC count, and (C) APC activation in autologous peripheral blood mononuclear cells after ex vivo PA2024 activation. Figure S7. Comparison of APC activation (CD54+ upregulation) between STAND and IMPACT.

Purpose: STAND, a randomized, phase II, open-label trial (NCT01431391), assessed sequencing of sipuleucel-T (an autologous cellular immunotherapy) with androgen deprivation therapy (ADT) in biochemically recurrent prostate cancer (BRPC) patients at high risk for metastasis.Experimental Design: Men with BRPC following prostatectomy and/or radiotherapy, a PSA doubling time ≤12 months, and no metastasis were enrolled. Patients were randomized (34/arm) to sipuleucel-T followed by ADT (started 2 weeks after sipuleucel-T completion), or ADT followed by sipuleucel-T (started 12 weeks after ADT initiation); ADT continued for 12 months in both arms. The primary endpoint was PA2024-specific T-cell response [enzyme-linked immunospot (ELISPOT)] over time.Results: PA2024-specific ELISPOT responses over time were similar between groups, except at week 6, where responses were higher with sipuleucel-T→ADT versus ADT→sipuleucel-T (P = 0.013). PA2024-specific T-cell proliferation responses, averaged across time points, were approximately 2-fold higher with sipuleucel-T→ADT versus ADT→sipuleucel-T (P = 0.001). PA2024-specific cellular and humoral responses and prostatic acid phosphatase–specific humoral responses increased significantly versus baseline (P < 0.001) and were maintained for 24 months (both arms). Median time-to-PSA recurrence was similar between arms (21.8 vs. 22.6 months, P = 0.357). Development of a PA2024-specific humoral response correlated with prolonged time-to-PSA progression (HR, 0.22; 95% CI, 0.08–0.67; P = 0.007). Sipuleucel-T with ADT was generally well tolerated.Conclusions: Sipuleucel-T→ADT appears to induce greater antitumor immune responses than the reverse sequence. These results warrant further investigation to determine whether this sequence leads to improved clinical outcomes, as well as the independent contribution of ADT alone in terms of immune activation. Clin Cancer Res; 23(10); 2451–9. ©2016 AACR.

Little is known about the true rate of pathogenic (P)/likely pathogenic (LP) germline alterations in Hispanic men with prostate cancer as most studies analyzing the prevalence of P/LP germline alterations were performed in a largely non-Hispanic white population (NHW).We performed a retrospective analysis of two separate cohorts of men with prostate cancer: (1) a multicenter cohort of 17,256 men who underwent germline testing in a CLIA-certified laboratory and (2) a single-center cohort of all men eligible for germline testing between 2018 and 2020. The proportions of P/LP alterations and variants of uncertain significance (VUS) were computed. Fisher's exact test was used to compare germline alteration rates for significance. A multivariate logistic regression was performed adjusting for demographic and clinical factors to examine factors associated with germline testing.In the multicenter cohort, the rate of P/LP germline alterations among self-reported Hispanic men was 7.1%, which was lower than self-reported NHW men (9.7% vs. 7.1%, p = 0.058), but was not statistically significant. The VUS rate was significantly higher among the Hispanic cohort (21.5% vs. 16.6%, p = 0.005). In the single-center cohort, 136 Hispanic patients were eligible for testing of which 34 underwent germline testing (26.1%, N = 34/136). Of all prostate cancer patients in the single-center cohort undergoing germline testing (n = 173), the rate of P/LP alterations in Hispanic patients was not significantly different compared to NHW patients (14.7% vs. 12.2%, p = 0.77). The rate of VUS in Hispanic patients was significantly higher than that of NHW patients (20.6% vs. 7.2%, p = 0.047).The P/LP germline alteration rate in our cohorts was similar between Hispanic and NHW men. The rate of VUS was significantly higher in Hispanic men, a consequence of undertesting in minority populations. These data support that Hispanic men with prostate cancer should be screened for germline testing similar to NHW men.

Purpose: STAND, a randomized, phase II, open-label trial (NCT01431391), assessed sequencing of sipuleucel-T (an autologous cellular immunotherapy) with androgen deprivation therapy (ADT) in biochemically recurrent prostate cancer (BRPC) patients at high risk for metastasis. Experimental Design: Men with BRPC following prostatectomy and/or radiotherapy, a PSA doubling time ≤12 months, and no metastasis were enrolled. Patients were randomized (34/arm) to sipuleucel-T followed by ADT (started 2 weeks after sipuleucel-T completion), or ADT followed by sipuleucel-T (started 12 weeks after ADT initiation); ADT continued for 12 months in both arms. The primary endpoint was PA2024-specific T-cell response [enzyme-linked immunospot (ELISPOT)] over time. Results: PA2024-specific ELISPOT responses over time were similar between groups, except at week 6, where responses were higher with sipuleucel-T→ADT versus ADT→sipuleucel-T (P = 0.013). PA2024-specific T-cell proliferation responses, averaged across time points, were approximately 2-fold higher with sipuleucel-T→ADT versus ADT→sipuleucel-T (P = 0.001). PA2024-specific cellular and humoral responses and prostatic acid phosphatase–specific humoral responses increased significantly versus baseline (P < 0.001) and were maintained for 24 months (both arms). Median time-to-PSA recurrence was similar between arms (21.8 vs. 22.6 months, P = 0.357). Development of a PA2024-specific humoral response correlated with prolonged time-to-PSA progression (HR, 0.22; 95% CI, 0.08–0.67; P = 0.007). Sipuleucel-T with ADT was generally well tolerated. Conclusions: Sipuleucel-T→ADT appears to induce greater antitumor immune responses than the reverse sequence. These results warrant further investigation to determine whether this sequence leads to improved clinical outcomes, as well as the independent contribution of ADT alone in terms of immune activation. Clin Cancer Res; 23(10); 2451–9. ©2016 AACR.

150 Background: Little is known about the clinical course of patients (pts) with metastatic hormone sensitive prostate cancer (mHSPC) who harbor alterations in the homologous recombination repair (HRR) pathway. Here, we examine the outcomes of men with mHSPC with HRR alterations. Methods: Single center, retrospective analysis of men with mHSPC who underwent next generation sequencing from 2015-2020. The primary endpoint was to assess the time from diagnosis of mHSPC to onset of castrate resistance (mCRPC), as defined by PCWG3 criteria, in pts with HRR alterations vs wild type (WT). Both somatic and germline HRR alterations were permitted. Univariate and multivariate Cox regression were used to assess the effect of HRR alterations on time to mCRPC. Secondary endpoints included time to mCRPC stratified by HRR gene and time to treatment failure (TTF) in HRR altered vs WT pts, stratified by therapy. Results: We identified 151 men with mHSPC for the study. Median age was 66 years and 62% (n = 93) had de novo metastatic disease. 25% (n = 37) had HRR alterations detected and the most common alterations were in BRCA2 (n = 15), ATM (n = 10), CDK12 (n = 7). 78.4% (n = 29) of alterations were somatic and 13.5% (n = 5) of pts had co-alterations in 2 HRR genes. Time to mCRPC was significantly decreased in pts with HRR alterations vs WT (12.7 vs 16.1 mos, HR- 1.95, p- 0.02). In multivariate analysis, the effect of HRR alterations on time to mCRPC remained statistically significant when adjusting for age, mHSPC therapy, presence of visceral metastases, and PSA (adjusted HR- 1.69, p-0.02). Stratified by individual HRR gene, pts with BRCA2, CDK12, or co-occurring alterations had significantly decreased time to mCRPC compared to other HRR alterations (Table). In terms of mHSPC therapy, 45.7% were treated with ADT alone, 27.8% with an androgen receptor signaling inhibitor (ARSI), and 26.5% with docetaxel. TTF was inferior in HRR altered vs WT pts (10.8 vs 13.8 mos, p-0.004, HR- 1.84). Stratified by therapy, TTF was inferior in HRR altered vs WT pts treated with ADT alone (8.9 vs 13.3 mos, p- 0.019, HR-1.94) and there was no significant difference in TTF in HRR altered vs WT pts treated with either the addition of an ARSI or docetaxel. Conclusions: HRR alterations are associated with worsened outcomes in mHSPC patients. Given the established role of PARP inhibitors in mCRPC, these data highlight an opportunity to explore the use of PARP inhibitors in mHSPC to potentially improve outcomes. [Table: see text]

Background: Little is known about the prevalence of germline alterations in Hispanic men with prostate cancer (PC). Here, we examine the rates of germline alterations in Hispanic men with PC, compare these rates to non-Hispanic white men, and examine factors associated with clinicians offering testing. Methods: Single center, retrospective analysis of patients (pts) with PC who self-identify as Hispanic and meet the NCCN criteria for germline testing. Pts who consented for testing underwent a commercial multigene germline assay. Among those tested, the proportion of pathogenic alterations and variants of uncertain significance (VUS) were computed in 20 genes associated with germline alterations in PC. This was compared to non-Hispanic white (NHW) pts who also underwent germline testing. Multivariate logistic regression was performed to assess clinical and demographic factors associated with clinicians offering germline testing and/or genetics referral. Results: We identified 136 Hispanic men with PC eligible for germline testing between 2018-2020. 26.1% (n=34) of pts underwent germline testing and among those tested, 14.7% (n=5/34) had a pathogenic alteration detected. Median age of the cohort was 70 years and 46.3% (n=63) had metastatic disease. Spanish was the primary language for 50% (n=68) and 14.0% (n=19) of pts had at least 1 first-degree relative with PC. Alterations were detected in ATM (n=2), CHEK2 (n=1), MSH2 (n=1), MSH6 (n=1). When stratified by disease status, the rate of pathogenic alterations was 7.7% (n=1/13) in localized and 19.0% (n=4/21) in metastatic disease. When compared to NHW pts who underwent testing (n=139), the rate of pathogenic alterations was not significantly different (14.7% in Hispanic vs 12.2% in NWH, p=0.77). The rate of VUS in Hispanic pts was significantly higher than NHW pts (20.6% in Hispanic vs 7.2% in NWH, p=0.047). In a multivariate model examining the factors associated with receipt of testing in Hispanic men (Table), the presence of metastatic disease and a family history of PC were positively associated with testing. Spanish as a primary language was negatively associated with testing. Age was not a significant predictor. Conclusions: Among Hispanic men who underwent germline testing, there was a similar rate of pathogenic germline alterations compared to NHW men. Among Hispanic men, primary Spanish speakers appear to have lower rates of germline testing. Bilingual strategies are needed to improve rates of testing to ensure equity in germline testing for all patients. [Table: see text]

110 Background: Given the technical limitations of obtaining tissue next-generation sequencing, there has been interest in blood ctDNA to assess genomic alterations in mCRPC. We examined the genomic landscape and prognostic significance of ctDNA in mCRPC. Methods: Single center retrospective analysis of mCRPC patients who underwent ctDNA genomic profiling using Guardant360. Overall survival (OS) and time to progression (TTP) were examined and stratified by the presence of tumor suppressor mutations (p53, PTEN, Rb), androgen receptor (AR) amplification or mutation, number of genomic alterations, and highest allelic fraction of detected mutations. Results: At the time of ctDNA collection, all patients (n=46) had mCRPC with bone metastases present in 100% of patients and visceral metastases present in 17.3%. Median age at ctDNA collection was 71 years, median time from CRPC diagnosis to ctDNA was 13 months (range 0-45), and median follow-up time from CRPC diagnosis was 17.5 months (4-40). The most common alterations present were TP53 mutation (41.3%), AR amplification (30.4%), and CDK6 amplification (21.7%). Actionable mutations were detected in BRCA1 (4.3%), BRCA2 (4.3%), ATM (2.2%), and PMS2 (2.2%). The median number of genomic alterations was 2 (0-8) and the median ctDNA allelic fraction was 4.6% (0-86.9%). Median OS of the cohort was 36 months. The presence of a tumor suppressor mutation, > 2 genomic alterations, and >5% mutation allelic fraction was associated with inferior OS (Table). In terms of time to progression on 1st line abiraterone or enzalutamide, the presence of an AR amplification or mutation was associated with significantly worse median TTP of 6.9 vs 13.5 months ( p- 0.015). Conclusions: ctDNA is frequently detected in mCRPC; and the type, number and frequency of alterations are potentially prognostic of OS in mCRPC. Ongoing studies are needed to assess concordance of ctDNA with tissue NGS and the predictability of ctDNA.[Table: see text]

Purpose: The CALGB performed a phase II multicenter study to evaluate the activity of oral capecitabine in patients with malignant mesothelioma (CALGB 39807). Patients and Methods: Between November 15, 2000 and August 31, 2001, 27 patients with mesothelioma were enrolled in this study. Capecitabine was administered at 2500 mg/m2 per day divided in two doses for 14 days followed by a seven-day break. Cycles were repeated every 21 days with restaging performed every two cycles and therapy continuing for up to six cycles. One patient withdrew from the study prior to receiving therapy and is removed from further analysis. Eligibility criteria included no prior treatment, PS 0–1 by CALGB criteria and histologically documented mesothelioma. Patient characteristics: gender; male 19 (73%), female seven; median age 70 (range 40–81); histology: epithelial 15 (58%), mixed eight (31%), unclassified three; site of origin pleura, 25 (96%); weight loss in previous six months of more than 10% in seven (27%), symptoms longer than six months in five (19%). Results: One patient (4%) had a confirmed PR while 10 (38%) achieved SD for 2–6 cycles. Ten patients (38%) had PD as their best response. There were three patients unevaluable for response and two early deaths. Median survival and failure free survival were 4.9 (95% CI 4–10.8) and 2.4 (95% CI 1.5–4.2) months respectively with a one-year survival of 23% (95% CI 11–49%). Grade three or greater toxicities encountered by at least 10% of patients included lymphopenia (12%), fatigue (12%), dehydration (12%) and diarrhea (15%). Three patients (12%) had grade three skin toxicity or hand–foot syndrome. One patient died of treatment related toxicity during cycle one. Conclusion: The antitumor activity of capecitabine is insufficient to warrant further exploration in patients with malignant mesothelioma.

We analyzed the efficacy of splenic irradiation in a population of patients with hematologic diseases. The records of the Radiation Oncology Division, Naval Medical Center San Diego were retrospectively reviewed for all patients treated with splenic irradiation (SI) between January 1, 1990 and March 1, 2001. The charts of 17 patients were identified: 5 patients had chronic myelogenous leukemia, 4 had chronic lymphocytic leukemia, 4 had idiopathic myelofibrosis, 2 had polycythemia vera, and 1 patient each had idiopathic thrombocytopenic purpura and acute myelogenous leukemia. Patient ages ranged from 37 to 88 years. Sixteen of 17 suffered from symptomatic splenomegaly. Twenty-six courses of splenic irradiation were delivered to these 17 patients. Treatment courses generally consisted of two fractions of 50 cGy in the first week, two fractions of 75 cGy the second week, and two fractions of 100 cGy the third week. Blood counts were checked prior to each treatment. Seven of the 17 patients died 1 month or less after SI due to the terminal nature of their disease. Twenty-two of 25 treatment courses for splenomegaly resulted in decreased pain and symptoms. Five patients required two treatment courses for splenomegaly, and one patient required five treatment courses. Three of four patients treated for thrombocytopenia demonstrated improvement, but only one was evaluable for more than 2 weeks due to disease-related mortality. Three of five patients treated for leukocytosis had significant improvement. In general, patients suffered few significant complications from this palliative intervention. Splenic irradiation can effectively palliate symptomatic splenomegaly in patients for whom splenectomy is not an option. Retreatment is possible. Splenic irradiation is less effective in the treatment of thrombocytopenia or leukocytosis.

e16516 Background: Identifying occult metastases in men with BRPC is critical, as treatment depends on disease state (biochemical recurrence vs oligometastatic disease). It is prudent to investigate pts for metastases, even men with low prostate-specific antigen (PSA) levels, to select appropriate salvage, local or systemic treatments. We evaluated baseline parameters of BRPC pts with occult metastases identified during screening for STAND (phase 2, NCT01431391). Methods: STAND eligibility criteria included prostate cancer primary therapy and PSA doubling time (PSADT) ≤12 months. Pts with metastases were excluded. We compared pts with and without metastases. Results: Of 99 screened pts, 68 entered STAND with non-metastatic BRPC, 11 (11%) failed screening due to metastases and 20 (20%) due to other reasons. In this small sample, no baseline parameters were identified that clearly distinguished between pts with or without metastases. For pts with metastases vs STAND pts, median age was similar (66 vs 65 y); all were Caucasian. Baseline median (range) PSA levels were numerically higher (4.3 [1.7–141.7] vs 2.4 [0.3–47.8] ng/mL) and PSADT values were numerically shorter (3.5 [1.1–7.6] vs 5.1 [1.0–16.4] months) for pts with metastases vs STAND pts, respectively. The proportion of pts with PSA > 10 ng/dL was 29% vs 19%, or PSADT < 6 months was 80% vs 59% for pts with metastases vs STAND pts, respectively. Baseline lactate dehydrogenase, alkaline phosphatase and hemoglobin levels were similar between groups. Conclusions: A substantial proportion (11%) of BRPC pts with presumed non-metastatic disease had undiagnosed occult metastases at low PSA levels. Such pts may benefit from closer monitoring with improved imaging technology, continuous androgen deprivation therapy or potentially docetaxel. While more rigorous screening (even at low PSA levels) may be advantageous, identifying such pts is challenging as their baseline parameters may not differ significantly vs BRPC pts with no metastases. In the future, detection of oligometastatic disease is likely to increase due to more sensitive imaging modalities, thus, the BRPC state will be reduced. Clinical trial information: NCT01431391.

Division of Oncology, University of Minnesota-Masonic Cancer Center, Minneapolis, Minnesota.Presented in part in abstract form at the AmericanSociety of Clinical Oncology annual meeting, May18–21, 1996 (Proc ASCO1996;15:427).Supported in part by grants CA21060 (C.C.).CA59518 (M.B.), CA32291 (G.P.C.), and CA16450(B.A.P.) from the National Cancer Institute.The research for CALGB 9051 was supported inpart by grants from the National Cancer Institute(research grant CA31946) to the Cancer and Leu-kemia Group B (Richard L. Schilsky, Chairman). Itscontents are solely the responsibility of the authorsand do not necessarily represent the official viewsof the National Cancer Institute.The following institutions participated in the studyand were supported in part by grants from theNational Cancer Institute: CALGB Statistical Office,Durham, NC (Stephen George, Ph.D.; CA33601);Christiana Care Health Services, Inc. CCOP, Wil-mington, DE (Irving M. Berkowitz, D.O.; CA45418);Community Hospital-Syracuse CCOP, Syracuse, NY(Jeffrey Kirshner, M.D.; CA45389); Dana FarberCancer Institute, Boston, MA (CA32291); NorrisCotton Cancer Center, Dartmouth Medical School,Lebanon, NH (L. Herbert Maurer, M.D.; CA04326);Kaiser Permanente CCOP, San Diego, CA(Jonathan A. Polikoff, M.D.; CA45374); Long IslandJewish Medical Center, Lake Success, NY (MarcCitron, M.D.; CA11028); Department of Oncology,McGill University, Montreal, Quebec (Brian Ley-land-Jones, M.D.; CA31809); Mount Sinai Schoolof Medicine, New York, NY (James F. Holland,M.D.; CA04457); North Shore University HospitalCCOP, Manhasset, NY (Vincent Vinciguerra, M.D.;CA35279); Rhode Island Hospital, Providence, RI(Louis A. Leone, M.D.; CA08025); Roswell ParkCancer Institute, Buffalo, NY (Ellis Levine, M.D.;CA02599); Southeast Cancer Control ConsortiumInc. CCOP, Goldsboro, NC (James N. Atkins, M.D.;CA45808); SUNY Health Science Center at Syra-cuse, Syracuse, NY (Stephen L. Graziano, M.D.;CA21060); University of Alabama-Birmingham,Birmingham, AL (Robert Diasio, M.D.; CA47545);University of California at San Diego, San Diego,CA (Stephen L. Seagren, M.D.; CA11789); Univer-sity of Iowa Hospitals, Iowa City, IA (Gerald H.Clamon, M.D.; CA47642); University of Massachu-setts Medical Center, Worcester, MA (Marc Stew-art, M.D.; CA37135); University of Minnesota, Min-neapolis, MN (Bruce A. Peterson, M.D.; CA16450);Wake Forest University School of Medicine, Win-ston-Salem, NC (David D. Hurd, M.D.; CA03927);Walter Reed Army Medical Center, Washington, DC(Nancy A. Dawson, M.D.; CA26806); WashingtonUniversity School of Medicine, St. Louis, MO (Nan-cy L. Bartlett, M.D.; CA77440).George P. Canellos, M.D., is a consultant for Bris-tol-Myers Squibb.Address for reprints: Todd H. Wasserman, M.D.,Professor of Radiation Oncology, Washington Uni-versity Medical Center, 216 South KingshighwayBoulevard, St. Louis, MO 63110.Received November 30, 1998; revision receivedApril 29, 1999; accepted July 15, 1999.

Sepsis is a common cause of morbidity and mortality. Neutrophils are the major defense against bacterial invasion, and granulocyte colony- stimulating factor (G-CSF) augments both neutrophil number and function. In our study, 160 rabbits were inoculated transtracheally with 0.5 mL of a solution containing 10(4) colony forming units per milliliter of Pasteurella multocida. Twenty-four hours later, chest x- rays and quantitative blood cultures demonstrated pneumonia and bacteremia. Therapy was then begun with penicillin G and either recombinant human G-CSF (rG-CSF; 5 to 8 micrograms/kg subcutaneously) or placebo every day for 5 days. Arterial blood gases and 23 other parameters of organ function were performed before inoculation and serially thereafter. All rabbits underwent histologic examination of organs at the time of septic death or when sacrificed on day 6. A total of 149 rabbits survived long enough to initiate therapy. A significant increase in leukocytes by day 4 was found in the rG-CSF-treated group. There was a trend towards improved survival in the rG-CSF group (77% v 67%; P = .13, n = 149). Analysis of pretreatment variables revealed sepsis-induced leukopenia (< or = 2,800/microL) as the only predictor of significantly improved survival with rG-CSF treatment (57% v 39%; P = .04, n = 73). The majority of the survival benefit occurred within the first 24 hours of treatment. This was before the time that a significant difference in mean white blood cell (WBC) count was observed between the study groups, making intravascular leukocytosis an unlikely explanation for the survival advantage in the rG-CSF group. No significant difference in laboratory variables reflecting organ function was demonstrated between the groups. Histologic grading of inflammation (0, normal, to 6, necrosis) in seven organs revealed that the surviving rabbits had mild but statistically significant increased inflammation in the liver, spleen, and noninoculated lung in the rG-CSF versus placebo groups (liver: 2.6 v 1.5, P < or = .0001; spleen: 3.2 v 2.3, P < or = .0001; and noninoculated lung: 2.9 v 2.5, P = .04). Administration of rG-CSF, in addition to penicillin G, in immune competent rabbits with gram-negative sepsis complicated by leukopenia significantly improved survival over antibiotics alone. The administration of rG-CSF in early sepsis for a short therapeutic duration was not associated with any clinically evident toxicity. Clinical trials using rG-CSF in septic patients with leukopenia are indicated.

Essential thrombocythemia (ET) is a myeloproliferative disorder characterized by isolated overproduction of platelets, thrombohemorrhagic complications, and a median age of 50-60. When it occurs in younger patients, the incidence of complications has been reported to be quite low, with a good long-term prognosis. We report a retrospective review of 13 patients with ET between the ages of 22 and 35 in which 11 were symptomatic at diagnosis, with only one remaining asymptomatic during follow-up. Three patients presented with potentially life-threatening complications (two myocardial infarctions, one stroke), although no deaths were observed. The majority of the nonlife-threatening complications were vaso-occlusive in nature, including erythromelalgia and transient neurologic symptoms. We conclude that ET in young adults is not always a benign disease and that potentially life-threatening complications are not rare. The optimum approach to treatment in this or any other age group remains uncertain.

Alloimmunization to donor class I HLA antigens represents a major obstacle to successful platelet transfusion therapy. It is desirable to distinguish alloimmunization from nonimmunologic causes of poor platelet survival to assess the need for HLA-matched, single-donor platelets. We describe a new in vitro assay for anti-HLA antibodies and report its application to the problem of platelet crossmatching. In contrast to previously described crossmatch techniques, the immunobead assay is specific for anti-HLA antibodies. The assay was used to evaluate 51 single-donor platelet transfusions given to seven patients from 35 different donors. Recipient plasma was assayed for antibodies directed against HLA antigens present on donor platelets. A one-hour posttransfusion corrected count increment of greater than or equal to 7,500 was considered a successful outcome. Twenty-nine of 33 (87.9%) transfusion episodes associated with a negative immunobead assay had successful outcomes. The four unsuccessful transfusions were associated with potential nonimmunologic causes of poor platelet survival. Only two of 18 (11.1%) episodes associated with a positive assay had successful outcomes. Only one unsuccessful transfusion episode was associated with a negative immunobead assay and a positive radiolabeled antiglobulin test result, which suggested that isolated alloantibodies to antigens other than class I HLA antigens are not a common cause of platelet refractoriness. Platelets stored in suspension at 4 degrees C or frozen in liquid nitrogen were found suitable for crossmatch testing.