Comparison of Circulating Tumor DNA Assays for Molecular Residual Disease Detection in Early-Stage Triple-Negative Breast Cancer

PURPOSE

Detection of circulating tumor DNA (ctDNA) in patients who have completed treatment for early-stage breast cancer is associated with a high risk of relapse, yet the optimal assay for ctDNA detection is unknown.

EXPERIMENTAL DESIGN

The cTRAK-TN clinical trial prospectively used tumor-informed digital PCR (dPCR) assays for ctDNA molecular residual disease (MRD) detection in early-stage triple-negative breast cancer. We compared tumor-informed dPCR assays with tumor-informed personalized multimutation sequencing assays in 141 patients from cTRAK-TN.

RESULTS

MRD was first detected by personalized sequencing in 47.9% of patients, 0% first detected by dPCR, and 52.1% with both assays simultaneously (P < 0.001; Fisher exact test). The median lead time from ctDNA detection to relapse was 6.1 months with personalized sequencing and 3.9 months with dPCR (P = 0.004, mixed-effects Cox model). Detection of MRD at the first time point was associated with a shorter time to relapse compared with detection at subsequent time points (median lead time 4.2 vs. 7.1 months; P = 0.02).

CONCLUSIONS

Personalized multimutation sequencing assays have potential clinically important improvements in clinical outcome in the early detection of MRD.

Abstract PD5-03: PD5-03 Comparison of a personalized sequencing assay and digital PCR for circulating tumor DNA based Molecular Residual Disease detection in early-stage triple negative breast cancer in the cTRAK-TN trial

Background: Detection of circulating tumour DNA (ctDNA) in patients (pts) who have completed treatment for early-stage breast cancer is associated with a high risk of future relapse. Identifying those at high risk of subsequent relapse may allow tailoring of further therapy to delay or prevent recurrence. Previous analysis of this cohort showed that tools capable of detecting ctDNA at lower concentrations are needed to increase sensitivity and lengthen the lead time between ctDNA detection and relapse. We compared ctDNA detection via a personalised sequencing assay to dPCR in patients from the cTRAK TN clinical trial. Methods: The cTRAK-TN trial recruited 161 pts into prospective ctDNA surveillance with dPCR, with ctDNA positive pts randomised to 1) CT staging plus pembrolizumab therapy for patients without relapse or 2) observation. Pts had serial post-treatment surveillance plasma samples collected every 3 months for up to 2 years. Whole exome sequencing (WES) was performed on tumor DNA from FFPE samples to design personalised Residual Disease and Recurrence (RaDaR®) multiplex PCR based NGS assays. Retrospectively, plasma DNA extracted from a minimum of 2mls banked plasma, was sequenced with personalised RaDaR assays, and ctDNA detection identified with a proprietary algorithm. dPCR assays tracked 1-2 mutations, as previously described. Primary endpoint was rate of positive ctDNA detection by 12 months from start of surveillance in both assays. Secondary endpoints were agreement in ctDNA detection between RaDaR and dPCR assays and lead-time between ctDNA detection and disease recurrence. Results: Overall, 147 pts and 241 tissue samples were subject to WES, and RaDaR assays were developed for 142 pts with sufficient plasma for testing. RaDaR assays tracked a median of 47 variants (range 33-56) per patient, and a total of 907 timepoints were analysed (median 6 timepoints per pt, range 1-11). With RaDaR, 39.4% (56/142) patients tested ctDNA positive during follow-up, with a median ctDNA detected level of 0.081% estimated variant allele fraction (eVAF). With dPCR, 35.2% (50/142) pts tested ctDNA positive. The ctDNA detection rate by 12 months from the start of ctDNA surveillance was 36.2% (95% CI; 27.6% – 43.7%) with RaDaR and 29.9% (95%CI; 21.6% – 37.3%) with dPCR. The overall test agreement between RaDaR and dPCR assays was 92.7% (95%CI; 90.7% – 94.4%). From a patient perspective, 58.7% pts were ctDNA negative for both assays, 32.9% ctDNA were positive for both assays and 8.6% presented discrepancies. ctDNA was detected by RaDaR but not by dPCR in 9 pts and it was detected by dPCR but not by RaDaR in 3 pts. Among ctDNA positive pts, 55.2% were first detected positive by RaDaR, 5.2% by dPCR, and 39.6% were detected at the same time-point (test of proportions, p&lt; 0.001). The median lead time from ctDNA detection to relapse was 7.1 months (95% CI 5.9 – 15.9%) with RaDaR and 5.7 months (95% CI 3.2% – 7.4%) with dPCR. Conclusion: The RaDaR personalised multi-mutation sequencing assay detected MRD with a longer median lead time prior to relapse, and with higher sensitivity, than dPCR mutation tracking assays. These findings have implications for the choice of ctDNA assay in clinical trials designed to treat patients at the point of MRD detection.

Citation Format: Maria Coakley, Prithika Sritharan, Guillermo Villacampa, Claire Swift, Kathryn Dunne, Lucy Kilburn, Katie Goddard, Patricia Rojas, Andy Joad, Warren Emmett, Charlene Knape, Karen Howarth, Peter S. Hall, Catherine Harper-Wynne, Tamas Hickish, Iain Macpherson, Alicia F. Okines, Andrew M. Wardley, Duncan Wheatley, Simon Waters, Rosalind Cutts, Isaac Garcia-Murillas, Judith Bliss, Nicholas Turner. PD5-03 Comparison of a personalized sequencing assay and digital PCR for circulating tumor DNA based Molecular Residual Disease detection in early-stage triple negative breast cancer in the cTRAK-TN trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD5-03.

Results of the c-TRAK TN trial: a clinical trial utilising ctDNA mutation tracking to detect molecular residual disease and trigger intervention in patients with moderate- and high-risk early-stage triple-negative breast cancer

BACKGROUND

Post-treatment detection of circulating tumour DNA (ctDNA) in early-stage triple-negative breast cancer (TNBC) patients predicts high risk of relapse. c-TRAK TN assessed the utility of prospective ctDNA surveillance in TNBC and the activity of pembrolizumab in patients with ctDNA detected [ctDNA positive (ctDNA+)].

PATIENTS AND METHODS

c-TRAK TN, a multicentre phase II trial, with integrated prospective ctDNA surveillance by digital PCR, enrolled patients with early-stage TNBC and residual disease following neoadjuvant chemotherapy, or stage II/III with adjuvant chemotherapy. ctDNA surveillance comprised three-monthly blood sampling to 12 months (18 months if samples were missed due to coronavirus disease), and ctDNA+ patients were randomised 2 : 1 to intervention : observation. ctDNA results were blinded unless patients were allocated to intervention, when staging scans were done and those free of recurrence were offered pembrolizumab. A protocol amendment (16 September 2020) closed the observation group; all subsequent ctDNA+ patients were allocated to intervention. Co-primary endpoints were (i) ctDNA detection rate and (ii) sustained ctDNA clearance rate on pembrolizumab (NCT03145961).

RESULTS

Two hundred and eight patients registered between 30 January 2018 and 06 December 2019, 185 had tumour sequenced, 171 (92.4%) had trackable mutations, and 161 entered ctDNA surveillance. Rate of ctDNA detection by 12 months was 27.3% (44/161, 95% confidence interval 20.6% to 34.9%). Seven patients relapsed without prior ctDNA detection. Forty-five patients entered the therapeutic component (intervention n = 31; observation n = 14; one observation patient was re-allocated to intervention following protocol amendment). Of patients allocated to intervention, 72% (23/32) had metastases on staging at the time of ctDNA+, and 4 patients declined pembrolizumab. Of the five patients who commenced pembrolizumab, none achieved sustained ctDNA clearance.

CONCLUSIONS

c-TRAK TN is the first prospective study to assess whether ctDNA assays have clinical utility in guiding therapy in TNBC. Patients had a high rate of metastatic disease on ctDNA detection. Findings have implications for future trial design, emphasising the importance of commencing ctDNA testing early, with more sensitive and/or frequent ctDNA testing regimes.

Abstract P2-01-10: Detection of ctDNA following surgery predicts relapse in breast cancer patients receiving primary surgery

Introduction: Identification of Molecular Residual Disease (MRD) by circulating tumour DNA (ctDNA) analysis has the potential to transform the clinical management of patients with early breast cancer. We present results from a proof-of-principle study to assess ctDNA analysis following primary surgery to identify MRD and anticipate which patients are at risk of relapse. Methods: Early breast cancer patients receiving primary surgery for breast cancer (48 total), enrolled in the PlasmaDNA/ITH sample collection studies were included in the analysis. Tumour DNA from FFPE samples was whole exome sequenced to identify patient specific mutations and design personalized Signatera ctDNA assays. Plasma samples were collected pre-surgery (n=31), 1-14 weeks post-surgery and prior to adjuvant therapy (n=48), and following adjuvant chemotherapy (n=36). Cell free DNA was extracted from a total of 144 plasma samples (median volume 3.6ml, range 1.8-4.7ml) and sequenced with Signatera ctDNA assays. Primary objective was to assess whether relapse free survival (RFS) and distant metastasis free survival (DMFS) are worse in patients with ctDNA detected at the post-surgery timepoint compared to those without ctDNA detected. Results: Median age was 50.5 years, 34 had hormone receptor positive HER2 negative (HR+HER2-), 5 HER2 positive and 9 triple negative breast cancer (TNBC), 32 were stage 1-2 and 16 were stage 3-4. At a median follow-up of 60 months post-surgery, 8 patients had relapsed. ctDNA was detected in the single post-surgery timepoint in 29% (14/48) of patients, and detected in 62.5% (5/8) of patients who relapsed. RFS in patients with ctDNA detected at a single post-surgery timepoint was worse than those with no detected ctDNA although it was not statistically significant (Hazard Ratio (HR): 3.7; 95% CI, 0.9-15.6; P=0.07), while ctDNA detection associated with worse DMFS (HR: 5.6; 95% CI, 1.1-29-3; P=0.04). DMFS at 4 years follow-up in those with MRD ctDNA detection was 0.78 (95% CI 0.47-0.92) and those without MRD detection was 0.97 (95% CI 0.80-0.99). In patients with a pre-surgical timepoint (n=31), 64.5% (20/31) had ctDNA detected. Detection of ctDNA at either pre-surgery or post-surgery was associated with worse outcomes compared to no ctDNA detection at both RFS (HR: 7.9; 95% CI, 0.9-64.7; P=0.05) and DMFS (HR: 6.7; 95% CI, 0.8-55.8; P=0.07). Conclusions: In this proof-of-principle study of early-stage breast cancer patients, ctDNA-detected MRD at a single post-surgical timepoint was associated with distant metastasis free survival. The majority of patients with ctDNA detected MRD did not relapse, during the period of follow-up, possibly suggesting activity of adjuvant therapy in these patients. Further assessment is warranted on the prognostic impact of ctDNA MRD detection, and its possible role in adjuvant chemotherapy selection.

Citation Format: Isaac Garcia-Murillas, Rosalind J Cutts, Lara Ulrich, Matthew Beaney, Marie Robert, Maria Coakley, Catey Bunce, Giselle WalshCrestani, Sarah Hrebien, Ekaterina Kalashnikova, Hsin-Ta Wu, Scott Dashner, Himanshu Sethi, Alexey Aleshin, Alistair Ring, Alicia Okines, Ian E Smith, Mitch Dowsett, Peter Barry, Nicholas C Turner. Detection of ctDNA following surgery predicts relapse in breast cancer patients receiving primary surgery [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-01-10.

Abstract 536: Molecular residual disease detection in early stage breast cancer with a personalized sequencing approach

Introduction: Detection of circulating tumor DNA (ctDNA) presents a strategy to identify Molecular Residual Disease (MRD) in patients with breast cancer. Tools capable of detecting ctDNA at lower concentrations are needed to increase sensitivity and lengthen lead time between ctDNA detection and relapse. We present results from a highly sensitive personalized sequencing approach for ctDNA detection of MRD based on multiple patient specific mutations.

Methods: 22 early breast cancer patients (12 hormone receptor positive HER2 negative (HR+HER2-), 7 HER2+ and 3 triple negative breast cancer (TNBC)) enrolled in the ChemoNEAR sample collection study were included. Tumor DNA from FFPE samples was Whole Exome Sequenced to identify patient specific mutations and design personalized Residual Disease and Recurrence (RaDaRTM) multiplex PCR assays. Cell free DNA was extracted from 147 plasma samples (median volume 4ml, range 0.5-5ml) and sequenced with RaDaR assays, with 10-61 variants (median 41) per panel, to 100,000x per locus. A matched single timepoint buffy coat was sequenced to identify confounding CHIP mutations. A proprietary algorithm was used to identify ctDNA. Tumor Sequencing of multiple biopsy timepoints was carried out for 14 patients (mean 2.8 samples per patient) and clonal populations estimated with Pyclone. For clusters of greater than 10 mutations, RaDaR panels were supplemented with additional variants for clonal tracking.

Results: At a median follow-up of 24.6 months post-surgery, MRD was identified in 100% (17/17) of relapsed patients, and in none of the 54 time points in the 5 patients that did not relapse (p=0.0002, Log rank test). Detection of ctDNA levels ranged from 7.4 parts per million (ppm), equivalent to Allele Frequency (AF) of 0.0007%, to 13,195ppm (1.3%) (median 625ppm and 0.06% AF). Median lead-time from ctDNA detection to clinical relapse in patients with extracranial disease relapse was 12.89 months (range 3.72-26.04). In three patients with brain only relapse, ctDNA was detected prior to relapse in all patients (3/3, 100%) albeit with a reduced lead time over clinical relapse (3.85, 4.21 and 5.65 months), which was not previously achievable with single mutation dPCR MRD-detection assays. In 8/14 patients with multiple tumor samples sequenced, multiple clones (mean 3.4 clones/patient) were identified, with heterogenous polyclonal relapse in 4/8 patients, and a single clone detectable in 4/8 patients.

Conclusions: In a retrospective, multi-center, proof-of-principle study of early stage breast cancer patients with personalized sequencing assays, ctDNA-detected MRD associates with relapse free survival and long lead time over clinical relapse. Sequencing based ctDNA testing can detect patients with brain-only relapses, with increased sensitivity over first generation dPCR-based ctDNA assays.

Citation Format: Rosalind J. Cutts, Maria Coakley, Isaac Garcia-Murillas, Lara Ulrich, Karen Howarth, Warren Emmett, Malcolm Perry, Pete Ellis, Charlene Knape, Stephen R. Johnston, Alistair Ring, Simon Russell, Abigail Evans, Anthony Skene, Duncan Wheatley, Mitch Dowsett, Ian E. Smith, Nicholas C. Turner. Molecular residual disease detection in early stage breast cancer with a personalized sequencing approach [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 536.

Impact of timing of adjuvant chemothapy for early breast cancer: the Royal Marsden Hospital experience

BACKGROUND

The optimal time to deliver adjuvant chemotherapy has not been defined.

METHODS

A retrospective study of consecutive patients receiving adjuvant anthracycline and/or taxane 1993-2010. Primary endpoint included 5-year disease-free survival (DFS) in patients commencing chemotherapy <31 versus ≥31 days after surgery. Secondary endpoints included 5-year overall survival (OS) and sub-group analysis by receptor status.

RESULTS

We identified 2003 eligible patients: 1102 commenced chemotherapy <31 days and 901 ≥31 days after surgery. After a median follow-up of 115 months, there was no difference in 5-year DFS rate with chemotherapy <31 compared to ≥31 days after surgery in the overall population (81 versus 82% hazard ratio (HR) 1.15, 95% confidence interval (95% CI) 0.92-1.43, p = 0.230). The 5-year OS rate was similar in patients who received chemotherapy <31 or ≥31 days after surgery (90 versus 91%, (HR 1.21, 95% CI 0.89-1.64, p = 0.228). For 250 patients with triple-negative breast cancer OS was significantly worse in patients who received chemotherapy ≥31 versus <31 days (HR = 2.18, 95% CI 1.11-4.30, p = 0.02).

DISCUSSION

Although adjuvant chemotherapy ≥31 days after surgery did not affect DFS or OS in the whole study population, in TN patients, chemotherapy ≥31 days after surgery significantly reduced 5-year OS; therefore, delays beyond 30 days in this sub-group should be avoided.

Correlation of rRNA gene amplicon pyrosequencing and bacterial culture for microbial compositional analysis of faecal samples from elderly Irish subjects

AIMS

The aim of this investigation was to establish the degree of correlation between measurements from culture-dependent microbiological techniques and from next generation sequencing technologies.

METHODS AND RESULTS

Data generated by both techniques were collected from faecal samples from 185 elderly Irish people involved in the ongoing ELDERMET study (http://eldermet.ucc.ie). The results for three groups of intestinal bacteria were compared. Bifidobacterium sp., Lactobacillus sp. and Enterobacteriaceae were enumerated on selective media through culture-dependent techniques, whereas proportions of these bacteria were determined through sequencing technology against the background of other bacteria. The Spearman's rank correlation coefficient determined a good correlation between results from culture-dependent microbiology and culture-independent techniques for all three bacterial groups assessed (correlation coefficients for Bifidobacterium sp., Lactobacillus sp. and Enterobacteriaceae were 0·380, 0·366 and 0·437, respectively).

CONCLUSION

Correlation between the two methods implies that a single method is capable of profiling intestinal Bifidobacterium, Lactobacillus and Enterobacteriaceae populations. However, both methods have advantages that justify their use in tandem.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first extensive study to compare bacterial counts from culture-dependent microbiological techniques and from next generation sequencing technologies.

Assessment of thrombin generation measured before and after cardiopulmonary bypass surgery and its association with postoperative bleeding

BACKGROUND

Bleeding after cardiopulmonary bypass (CPB) is a major cause of morbidity and mortality and consumes large amounts of blood. Identifying patients at increased risk of bleeding secondary to hemostatic impairment may improve clinical outcomes by allowing early intervention.

METHODS

This present study recruited 77 patients undergoing CPB and measured coagulation screens, coagulation factors, TEG(®), Rotem(®) and thrombin generation (TG) before surgery and 30 min after heparin reversal. The tests were analyzed to investigate whether they identified patients at increased risk of excess bleeding (defined as > 1000 mL) in the first 24 h postoperatively.

RESULTS

Patients who bled > 1000 mL had a lower: platelet count (P < 0.02), factors (F)IX, X and XI (P < 0.005), endogenous thrombin potential (ETP) and an initial rate of TG (P < 0.02) and higher activated partial thromboplastin time (aPTT) (P < 0.001) than patients who bled < 1000 mL. Receiver operating characteristic (ROC) analysis was significant for post-operative TG and aPTT (P < 0.001). Furthermore, reduced pre-operative TG was associated with increased postoperative bleeding (P < 0.02). Pre- and postoperative TG were correlated (ρ = 0.7, P < 0.001). TEG(®), Rotem(®) and prothrombin time (PT) at either time point were not associated with increased bleeding.

CONCLUSION

These data suggest that pre-operative defects in the propagation phase of hemostasis are exacerbated during CPB, contributing to bleeding post-CPB. TG taken both pre- and postoperatively could potentially be used to identify patients at an increased risk of bleeding post-CPB.

Cheese Manufacture with Milk with Elevated Conjugated Linoleic Acid Levels Caused by Dietary Manipulation

The objective of this study was to assess the effect of dietary supplementation of cows on pasture with sunflower oil for conjugated linoleic acid (cis-9, trans-11 CLA) enrichment of milk, for the production of CLA-enriched cheese. A group of 40 autumn-calving dairy cows were assigned to either a control group (indoor feeding on grass silage ad libitum and 6 kg/d of a typical indoor concentrate) or an experimental group (on pasture, being fed 6 kg of a supplement containing 100 g/kg of sunflower oil per d). These diets were fed for 16 d, during which time milk was collected for pilot-scale hard cheese manufacture. The pasture-based diet with sunflower oil resulted in a significant effect on the milk fatty acid CLA content. The concentration of cis-9, trans-11 CLA in the milk produced from cows on this diet increased to 2.22 g/100 g of fatty acid methyl esters (FAME) after 14 d, compared with 0.46 g/100 g of FAME in milk produced on the control indoor diet. The content of cis-9, trans-11 CLA in the cheese manufactured from the indoor control milk was 0.78 g/100 g of FAME and that from the pasture-based sunflower oil milk was 1.93 g/100 g of FAME. The cheese was assessed during the ripening period and CLA concentrations were stable throughout the 6 mo of ripening. Other cheese variables (microbiology, composition, flavor, free AA) were monitored during the ripening period, and the cheese with the elevated CLA concentrations compared favorably with the control cheese. Thus, a pasture-based diet supplemented with an oil source rich in linoleic acid resulted in an enhanced CLA content of bovine milk fat, compared with an indoor grass silage-based diet.

Use of the platelet function analyser (PFA-100) to quantify the effect of low dose aspirin in patients with ischaemic heart disease

Continuing aspirin up until surgery in cardiac surgical patients may increase peri-operative blood loss. It is possible that there is a subset of patients particularly sensitive to aspirin. The platelet function analyser (PFA-100) can demonstrate the antiplatelet effect of aspirin. This study was designed to assess the effect of daily 75 mg aspirin on platelet function, as measured by the PFA-100, in 92 patients with ischaemic heart disease. Patients were classified into three groups according to their PFA-100 results; aspirin hyper-responders (16%), aspirin normal responders (33%) and aspirin non-responders (51%). The PFA-100 has potential as a screening tool to identify patients who are either hyper-responsive or resistant to aspirin. Pre-operative PFA-100 screening to isolate aspirin hyper-responders could enable the vast majority of patients to continue with aspirin therapy pre-operatively, avoiding the risks of stopping treatment.

Conjugated linoleic acid biosynthesis by human-derived Bifidobacterium species

AIMS

To assess strains of Lactobacillus, Lactococcus, Pediococcus and Bifidobacterium for their ability to produce the health-promoting fatty acid conjugated linoleic acid (CLA) from free linoleic acid.

METHODS AND RESULTS

In this study, strains of Lactobacillus, Lactococcus, Pediococcus and Bifidobacterium were grown in medium containing free linoleic acid. Growth of the bacteria in linoleic acid and conversion of the linoleic acid to CLA was assessed. Of the bacteria assessed, nine strains of Bifidobacterium produced the c9, t11 CLA isomer from free linoleic acid. The t9, t11 CLA isomer was also produced by some strains, but at much lower concentrations.

CONCLUSIONS

The production of CLA by bifidobacteria exhibited considerable interspecies variation. Bifidobacterium breve and B. dentium were the most efficient CLA producers among the range of strains tested, with B. breve converting up to 65% linoleic acid to c9, t11 CLA when grown in 0.55 mg ml(-1) linoleic acid. Strains also varied considerably with respect to their sensitivity to linoleic acid.

SIGNIFICANCE AND IMPACT OF THE STUDY

The production of CLA by probiotic bifidobacteria offers a possible mechanism for some health-enhancing properties of bifidobacteria and provides novel opportunities for the development of functional foods.

An intracranial neoplasm complicating labour

We present a case in which a 27-year-old primigravida was found to have an intracranial tumour during the first stage of labour. We review previous reports of similar cases and discuss the management options.

Pharmacokinetics of flunixin meglumine in donkeys, mules, and horses

OBJECTIVE

To compare serum disposition of flunixin meglumine after i.v. administration of a bolus to horses, donkeys, and mules.

ANIMALS

3 clinically normal horses, 5 clinically normal donkeys, and 5 clinically normal mules.

PROCEDURE

Blood samples were collected at time zero (before) and 5, 10, 15, 30, and 45 minutes, and at 1, 1.25, 1.5, 1.75, 2, 2.5, 2.75, 3, 3.5, 4, 4.5, 5, 5.5, 6, and 8 hours after i.v. administration of a bolus of flunixin meglumine (1.1 mg/kg of body weight). Serum was analyzed in duplicate by the use of high-performance liquid chromatography for determination of flunixin meglumine concentrations. The serum concentration-time curve for each horse, donkey, and mule were analyzed separately to estimate noncompartmental pharmacokinetic variables

RESULTS

Mean (+/-SD) area under the curve for donkeys (646 +/- 148 minute x microg/ml) was significantly less than for horses (976 +/- 168 minute x microg/ml) or for mules (860 +/- 343 minute x microg/ml). Mean residence time for donkeys (54.6 +/- 7 minutes) was significantly less than for horses (110 +/- 24 minutes) or for mules (93 +/- 30 minutes). Mean total body clearance for donkeys (1.78 +/- 0.5 ml/kg/h) was significantly different from that for horses (1.14 +/- 0.18 ml/kg/h) but not from that for mules (1.4 +/- 0.5 ml/kg/h). Significant differences were not found between horses and mules for any pharmacokinetic variable.

CONCLUSION AND CLINICAL RELEVANCE

Significant differences exist with regard to serum disposition of flunixin meglumine in donkeys, compared with that for horses and mules. Consequently, flunixin meglumine dosing regimens used in horses may be inappropriate for use in donkeys.

Application and evaluation of the phage resistance- and bacteriocin-encoding plasmid pMRC01 for the improvement of dairy starter cultures

The conjugative 63-kb lactococcal plasmid pMRC01 encodes bacteriophage resistance and production of and immunity to a novel broad-spectrum bacteriocin, designated lacticin 3147 (M.P. Ryan, M.C. Rea, C. Hill, and R.P. Ross, Appl. Environ. Microbiol. 62:612-619, 1996). The phage resistance is an abortive infection mechanism which targets the phage-lytic cycle at a point after phage DNA replication. By using the genetic determinants for bacteriocin immunity encoded on the plasmid as a selectable marker, pMRC01 was transferred into a variety of lactococcal starter cultures to improve their phage resistance properties. Selection of resulting transconjugants was performed directly on solid media containing the bacteriocin. Since the starters exhibited no spontaneous resistance to the bacteriocin as a selective agent, this allowed the assessment of the transfer of the naturally occurring plasmid into a range of dairy starter cultures. Results demonstrate that efficient transfer of the plasmid was dependent on the particular recipient strain chosen, and while high-frequency transfer (10(-3) per donor) of the entire plasmid to some strains was observed, the plasmid could not be conjugated into a number of starters. In this study, transconjugants for a number of lactococcal starter cultures which are phage resistant and bacteriocin producing have been generated. This bacteriocin-producing phenotype allows for control of nonstarter flora in food fermentations, and the phage resistance property protects the starter cultures in industry. The 63-kb plasmid was also successfully transferred into Lactococcus lactis MG1614 cells via electroporation.

"Normal" childhood sexual play and games: differentiating play from abuse

Recent recognition of child-to-child and adolescent-to-child sexual abuse raises the question, for the courts, educators, clinicians, and lay individuals, where do we draw the line between normal childhood sexual play, and abuse. This paper presents the results of a survey on normative childhood sexual play and games experiences that was distributed to 300 undergraduates at an all women's college. One hundred-twenty-eight returned the survey, 85% of whom described a childhood sexual game experience. Of these women, 44% described cross-gender play and there was a trend for women who had described cross-gender experiences to have seen the play as involving persuasion, manipulation, or coercion. A strong relationship was found between abuse and cross-gender play. Level of physical involvement in the game was correlated with perceptions of normality. A typology of six kinds of sexual play experiences was derived. Results are discussed in terms of their relation to differentiating childhood sexual abuse from play and gender socialization influences relating to the role rehearsal of coercive or manipulative relationships.