Enhancing clinical decision support with genomic tools in breast cancer: A Scottish perspective

INTRODUCTION

The Oncotype DX Breast RS test has been adopted in Scotland and has been the subject of a large population-based study by a Scottish Consensus Group to assess the uptake of the recurrence score (RS), evaluate co-variates associated with the RS and to analyse the effect it may have had on clinical practice.

MATERIALS & METHODS

Pan-Scotland study between August 2018-August 2021 evaluating 833 patients who had a RS test performed as part of their diagnostic pathway. Data was extracted retrospectively from electronic records and analysis conducted to describe change in chemotherapy administration (by direct comparison with conventional risk assessment tools), and univariate/multivariate analysis to assess relationship between covariates and the RS.

RESULTS

Chemotherapy treatment was strongly influenced by the RS (p < 0.001). Only 30 % of patients received chemotherapy treatment in the intermediate and high risk PREDICT groups, where chemotherapy is considered. Additionally, 55.5 % of patients with a high risk PREDICT had a low RS and did not receive chemotherapy. There were 17 % of patients with a low risk PREDICT but high RS who received chemotherapy. Multivariate regression analysis showed the progesterone receptor Allred score (PR score) to be a strong independent predictor of the RS, with a negative PR score being associated with high RS (OR 4.49, p < 0.001). Increasing grade was also associated with high RS (OR 3.81, p < 0.001). Classic lobular pathology was associated with a low RS in comparison to other tumour pathology (p < 0.01). Nodal disease was associated with a lower RS (p = 0.012) on univariate analysis, with menopausal status (p = 0.43) not influencing the RS on univariate or multivariate analysis.

CONCLUSIONS

Genomic assays offer the potential for risk-stratified decision making regarding the use of chemotherapy. They can help reduce unnecessary chemotherapy treatment and identify a subgroup of patients with more adverse genomic tumour biology. A recent publication by Health Improvement Scotland (HIS) has updated guidance on use of the RS test for NHS Scotland. It suggests to limit its use to the intermediate risk PREDICT group. Our study shows the impact of the RS test in the low and high risk PREDICT groups. The implementation across Scotland has resulted in a notable shift in practice, leading to a significant reduction in chemotherapy administration in the setting of high risk PREDICT scores returning low risk RS. There has also been utility for the test in the low risk PREDICT group to detect a small subgroup with a high RS. We have found the PR score to have a strong independent association with high risk RS. This finding was not evaluated by the key RS test papers, and the potential prognostic information provided by the PR score as a surrogate biomarker is an outstanding question that requires more research to validate.

Impaired Cardiac and Skeletal Muscle Energetics Following Anthracycline Therapy for Breast Cancer

BACKGROUND

Anthracycline-related cardiac toxicity is a recognized consequence of cancer therapies. We assess resting cardiac and skeletal muscle energetics and myocyte, sarcomere, and mitochondrial integrity in patients with breast cancer receiving epirubicin.

METHODS

In a prospective, mechanistic, observational, longitudinal study, we investigated chemotherapy-naive patients with breast cancer receiving epirubicin versus sex- and age-matched healthy controls. Resting energetic status of cardiac and skeletal muscle (phosphocreatine/gamma ATP and inorganic phosphate [Pi]/phosphocreatine, respectively) was assessed with 31P-magnetic resonance spectroscopy. Cardiac function and tissue characterization (magnetic resonance imaging and 2D-echocardiography), cardiac biomarkers (serum NT-pro-BNP and high-sensitivity troponin I), and structural assessments of skeletal muscle biopsies were obtained. All study assessments were performed before and after chemotherapy.

RESULTS

Twenty-five female patients with breast cancer (median age, 53 years) received a mean epirubicin dose of 304 mg/m2, and 25 age/sex-matched controls were recruited. Despite comparable baseline cardiac and skeletal muscle energetics with the healthy controls, after chemotherapy, patients with breast cancer showed a reduction in cardiac phosphocreatine/gamma ATP ratio (2.0±0.7 versus 1.1±0.5; P=0.001) and an increase in skeletal muscle Pi/phosphocreatine ratio (0.1±0.1 versus 0.2±0.1; P=0.022). This occurred in the context of increases in left ventricular end-systolic and end-diastolic volumes (P=0.009 and P=0.008, respectively), T1 and T2 mapping (P=0.001 and P=0.028, respectively) but with preserved left ventricular ejection fraction, mass and global longitudinal strain, and no change in cardiac biomarkers. There was preservation of the mitochondrial copy number in skeletal muscle biopsies but a significant increase in areas of skeletal muscle degradation (P=0.001) in patients with breast cancer following chemotherapy. Patients with breast cancer demonstrated a reduction in skeletal muscle sarcomere number from the prechemotherapy stage compared with healthy controls (P=0.013).

CONCLUSIONS

Contemporary doses of epirubicin for breast cancer treatment result in a significant reduction of cardiac and skeletal muscle high-energy 31P-metabolism alongside structural skeletal muscle changes.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT04467411.

Energetic and myocellular pathways in cardiac and skeletal muscle following anthracycline chemotherapy

Background

Anthracycline-related cardiac dysfunction is a recognised consequence of cancer therapies. Here we assess resting cardiac and skeletal muscle energic status as an early mechanistic pathway of myocyte derangement and explore molecular targets of skeletal myocyte metabolism, protein synthesis/degradation and mitochondrial biogenesis signalling.

Methods

We conducted a prospective, mechanistic, observational, longitudinal study of chemotherapy-naive breast cancer patients undergoing anthracycline-based chemotherapy, compared to a healthy control group. 31P-Magnetic Resonance spectroscopy in cardiac and skeletal muscle (phosphocreatine/gamma adenosine triphosphate (PCr/yATP) and inorganic phosphate/phosphocreatine (Pi/PCr) ratios respectively), cardiac magnetic resonance (CMR) imaging inclusive of T1 and T2 mapping, echocardiography-derived global longitudinal strain function, serum NT-pro-BNP and skeletal muscle biopsies from the right vastus lateralis were assessed before and after 3 cycles of Flurouracil, Epirubicin and Cyclophosphamide followed by 3 cycles of Docetaxel. Statistical significance was set at p&lt;0.05.

Results

Twenty-five female breast cancer patients (median age 53 years, range 32–74 years) receiving a mean epirubicin dose 307 mg/m2) and twenty-eight controls (median age 44 years, range 23–65) were recruited. All study assessments in breast cancer patients at pre-chemotherapy stage were comparable to the matched healthy controls. However, following chemotherapy, breast cancer patients demonstrated a small but significant reduction in cardiac function (global longitudinal strain −22.9±3.9 vs −19.1±3.3%, p=0.01 and CMR-derived ejection fraction 65±5 vs 62±4%, p=0.047), a mild increase in CMR-derived indexed left ventricular volumes (end diastolic 65±10 vs 74±11 ml/m2, p=0.014 and end systolic 23±5 vs 28±5 ml/m2, p=0.01) as well as an increase in left ventricular T1 and T2-mapping (1289±29 vs 1321±31 ms, p=0.004 and 50±4 vs 55±7 ms, p=0.027, respectively) and serum NT-Pro-BNP (49±25 vs 108±84 pg/m, p=0.008). After epirubicin, there was significant reduction in cardiac PCr/yATP ratio (2.0±0.7 vs 1.2±0.6, p=0.007) and a significant increase in skeletal muscle Pi/PCr ratio (0.13±0.04 vs 0.22±0.2, p=0.008) – Figure 1.

Following chemotherapy, there was significant upregulation of skeletal myocyte protein synthesis (mammalian target of rapamycin, 0.44±0.4 vs 0.53±0.2, p&lt;0.001) and degradation (Calcium/calmodulin dependent protein kinase II, 1.4±0.7 vs 2.7±1.1, p&lt;0.001), metabolism (peroxisome proliferator-activated receptor gamma, 0.35±0.2 vs 0.60±0.1, p&lt;0.001) and muscle mass regulator myostatin-2 (0.16±0.1 vs 0.24±0.1, p&lt;0.001).

Conclusion

Contemporary doses of epirubicin for breast cancer result in significant reduction of cardiac and skeletal muscle high energy 31P-metabolism alongside skeletal myocellular alterations of protein synthesis and metabolic regulation pathways.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Tenovus ScotlandNHS Grampian Endowment fund

Not all small HER2 positive breast cancers have the same clinical outcome in the North-East of Scotland

HER2-positive breast cancers, representing up to 20% of all breast cancers, are more aggressive and have poorer outcomes. Systemic therapy has been proven to prevent disease recurrence and improve survival. Existing literature provides only limited evidence to support this in smaller HER2-positive tumors. The study aimed to evaluate HER-2 positive breast cancer management and treatment of all T1N0 tumors in the North of Scotland, diagnosed 2012-2019. Clinical-pathological details, comorbidities, treatments and clinical events were retrieved from the Scottish North Cancer Alliance audit database and analyzed using univariate and multivariate analysis including cox-regression and log-rank testing (SPSSv23).Overall, 299 patients (41% screen detected/ 56.9% symptomatic /2.1% other), median age 63 years and median tumor size 13 mm, were included. Most cancers were grade 2/3 (43.1%/ 55.5%). Most patients (59.5%) received treatment with trastuzumab (tT); 40.8% concurrent with chemotherapy and endocrine therapy. 7.7% of patients received neo adjuvant chemotherapy. Median follow-up time was 2.6 years, with recurrence on average occurring 2.9 years after diagnosis. Patients receiving trastuzumab were younger, had a higher grade and larger size tumor. 78.5% of patients in the untreated group (non-tT) were ER positive compared to 65.2% in the treated group (tT). Trastuzumab significantly lowered breast cancer recurrence (Tt=3.4% versus non-Tt=8.3%, p = 0.022 HR= 0.096, 95% CI 0.025-0.361). In conclusion, receiving anti-HER2 treatment significantly improved clinical outcome in this T1N0 patient group. Consideration, at the very least informed discussions with patients, should be undertaken to treat these early stage HER2-positive breast cancers.

Variation in chemotherapy prescribing rates and mortality in early breast cancer over two decades: a national data linkage study

Background

Regional variation in clinical practice may identify differences in care, reveal inequity in access, and explain inequality in outcomes. The study aim was to measure geographical variation in Scotland for adjuvant chemotherapy use and mortality in early-stage breast cancer.

Patients and methods

In this retrospective cohort study using population cancer registry-based data linkage, patients with surgically treated early breast cancer between 2001 and 2018 were identified from the Scottish Cancer Registry. Geographical regions considered were based on NHS Scotland organisational structure including 14 territorial Health Boards as well as three regional Cancer Networks. Regional variation in the proportion receiving chemotherapy, breast cancer mortality and all-cause mortality was investigated. Inter-regional comparisons of chemotherapy use were adjusted for differences in case mix using logistic regression. Comparison of breast cancer-specific mortality and all-cause mortality used regression with a parametric survival model. Time trends were assessed using moving average plots.

Results

Chemotherapy use ranged from 35% to 46% of patients across Health Boards without adjustment. Variation reduced between 2001 and 2018. Following adjustment for clinical case mix, variation between cancer networks was within 3 percentage points, but up to 10 percentage points from the national average in some Health Boards. Differences in breast cancer mortality and all-cause mortality between cancer networks were modest, with hazard ratios of between 0.933 (95% confidence interval 0.893-0.975) and 1.041 (1.002-1.082) compared with the national average. Survival improved over the time period studied.

Conclusion

With adequate case mix adjustment, variation in adjuvant chemotherapy use for early breast cancer in Scotland is small, with a trend towards greater convergence in practice and improved mortality outcomes in more recent cohorts. This suggests very limited regional inequity in access and convergence of clinical practice towards risk-stratified treatment recommendations. Outliers require assessment to understand the reasons for variance.

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A cohort study including the Scottish population of surgically treated early breast cancer patients from 2001 to 2018.

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With adequate case mix adjustment, regional variation in adjuvant chemotherapy use was small, but with notable outliers.

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Over time there was a trend towards greater convergence in practice towards risk-stratified treatment recommendations.

362 Comparison of PREDICT Score to Oncotype Dx Score in Early Invasive Breast Cancer

Aim

The PREDICT score is used to help define decisions about benefits of chemotherapy in early invasive breast cancer. With a PREDICT score of 5% or more chemotherapy should be considered, 3% to 4% is a borderline decision and less than 3% chemotherapy is not pursued. We set out to compare the PREDICT score to Oncotype Dx recurrence score (RS), which predicts chemotherapy benefit based on 21-gene breast cancer assay.

Method

Data for patient and tumour characteristics, and treatment choice was collected from electronic patient records of 98 patients who had an RS score done between February 2017-September 2020. This data was then compared to the patients’ PREDICT scores.

Results

98 patients were analysed with 2 excluded due to having nodal macro-metastases. Mean patient age was 53 years with an average tumour size of 27mm. 31/96 (32%) patients had a PREDICT score ≥5%, with 21/31 (68%) having a low RS score (&lt;26). 57/96 (59%) patients had a PREDICT score of 3-4%, with 40/57 (70%) having a low RS score. 8/96 (8%) patients had a PREDICT score of &lt; 3%, with 7/8 (88%) having a low RS score. Additionally, 7/8 (88%) patients in this group were pre-menopausal.

Conclusions

68% of patients in the ≥5% PREDICT group had a low RS score and so have avoided chemotherapy. In the 3-4% group, approximately 1 in 3 tested were shown to have a chemotherapy benefit. In the &lt;3% group most patients were pre-menopausal, and chemotherapy was safely avoided. A bigger dataset and comparison to other health boards is required.

Does the gut microbiome environment influence response to systemic breast cancer treatment?

The gut microbiome is a novel player in the pathogenesis and treatment of breast cancer. The term “microbiome” is used to describe the diverse community of micro-organisms existing within the gastrointestinal tract. The gut microbiome plays an important role in oestrogen metabolism through its ability to deconjugate oestrogens within the gut resulting in their reabsorption. Therefore, it is not unsurprising that “dysbiosis”, the disruption of normal gut microbiota composition, is now thought to play a role in the development of the disease, as women with breast cancer have been shown to have altered gut microbiota and this has been correlated with tumour characteristics. There is emerging evidence to suggest that the gut microbiota may also impact on breast cancer treatment, by mediating both drug efficacy and toxicity. The present review will discuss the influence of the gut microbiota on systemic treatments for breast cancer, including chemotherapy, anti-human epidermal growth factor receptor 2 (HER2) therapy, endocrine therapy and immunotherapy as well as other targeted treatments.

Regulation of cellular sphingosine-1-phosphate by sphingosine kinase 1 and sphingosine-1-phopshate lyase determines chemotherapy resistance in gastroesophageal cancer

Background

Resistance to chemotherapy is common in gastroesophageal cancer. Mechanisms of resistance are incompletely characterised and there are no predictive biomarkers in clinical practice for cytotoxic drugs. We used new cell line models to characterise novel chemotherapy resistance mechanisms and validated them in tumour specimens to identify new targets and biomarkers for gastroesophageal cancer.

Methods

Cell lines were selected for resistance to oxaliplatin, cisplatin and docetaxel and gene expression examined using Affymetrix Exon 1.0 ST arrays. Leads were validated by qRT-PCR and HPLC of tumour metabolites. Protein expression and pharmacological inhibition of lead target SPHK1 was evaluated in independent cell lines, and by immunohistochemistry in gastroesophageal cancer patients.

Results

Genes with differential expression in drug resistant cell lines compared to the parental cell line they were derived from, were identified for each drug resistant cell line. Biological pathway analysis of these gene lists, identified over-represented pathways, and only 3 pathways - lysosome, sphingolipid metabolism and p53 signalling- were identified as over-represented in these lists for all three cytotoxic drugs investigated. The majority of genes differentially expressed in chemoresistant cell lines from these pathways, were involved in metabolism of glycosphingolipids and sphingolipids in lysosomal compartments suggesting that sphingolipids might be important mediators of cytotoxic drug resistance in gastroeosphageal cancers . On further investigation, we found that drug resistance (IC50) was correlated with increased sphingosine kinase 1(SPHK1) mRNA and also with decreased sphingosine-1-phosphate lysase 1(SGPL1) mRNA. SPHK1 and SGPL1 gene expression were inversely correlated. SPHK1:SGPL1 ratio correlated with increased cellular sphingosine-1-phosphate (S1P), and S1P correlated with drug resistance (IC50). High SPHK1 protein correlated with resistance to cisplatin (IC50) in an independent gastric cancer cell line panel and with survival of patients treated with chemotherapy prior to surgery but not in patients treated with surgery alone. Safingol a SPHK1 inhibitor, was cytotoxic as a single agent and acted synergistically with cisplatin in gastric cancer cell lines.

Conclusion

Agents that inhibit SPHK1 or S1P could overcome cytotoxic drug resistance in gastroesophageal cancer. There are several agents in early phase human trials including Safingol that could be combined with chemotherapy or used in patients progressing after chemotherapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1718-7) contains supplementary material, which is available to authorized users.

Early clinical experience with the Anaconda re-deployable endograft in 106 patients with abdominal aortic aneurism: the west of Scotland Anaconda registry

Endovascular repair of abdominal aortic aneurysm is a common procedure and not without complications. The aim of this study was to evaluate the early results of the Anaconda endograft (Vascutek Ltd., Inchinnan, Scotland, UK) in 106 patients in three hospitals in the west of Scotland. A prospective registry of 106 consecutive patients undergoing endoluminal repair of their abdominal aortic aneurysms using the Anaconda device was set up to record the clinical outcomes, with a mean follow-up of two years. There was no 30-day perioperative mortality in the 106 patients. Only type II endoleaks were detected on serial computed tomography scanning at follow-up. Technical success was achieved in 99% (105/106) in this study; one patient was converted to open surgical repair. Two cases of proximal device migration (>1 cm) were detected at one month and 19 months, respectively, with no associated endoleak or sac enlargement. Five cases of endograft limb thrombosis were noted in this study. Our early clinical experience with the Anaconda endograft compares favourably with other commercially available endografts in the treatment of abdominal aortic aneurysms. The main advantages of this device are that it is re-deployable and that it has a magnetic wire system which makes it easy to implant.

Immunization information systems progress - United States, 2005

Immunization registries are confidential, computerized information systems that collect and consolidate vaccination data from multiple health-care providers, generate reminder and recall notifications, and assess vaccination coverage within a defined geographic area. A registry with added capabilities, such as vaccine management, adverse event reporting, lifespan vaccination histories, and linkages with electronic data sources, is called an immunization information system (IIS). This report summarizes data from CDC's 2005 Immunization Information System Annual Report (IISAR), a survey of grantees in 50 states, five cities, and the District of Columbia (DC) that receive funding under section 317b of the Public Health Service Act. These data indicated that approximately 56% of U.S. children aged <6 years participated in an IIS, an increase from 48% in 2004. Moreover, 75% percent of public vaccination provider sites and 44% of private vaccination provider sites submitted vaccination data to an IIS during July-December 2005. These findings underscore the need to increase the number of participating children, from the current 13 million to approximately 21 million, to assure 95% participation of children aged <6 years and improve the effectiveness of U.S. immunization programs.

Colorectal stenting for colonic obstruction: the indications, complications, effectiveness and outcome--5 year review

INTRODUCTION

Currently self-expanding metallic stents are being used for palliation and acute decompression of colonic obstruction. The aim of this study is to review our experience of using these metallic stents over a 5-year period.

MATERIALS AND METHODS

Case records of 102 patients who had colorectal stenting between 1998 and 2004 were reviewed retrospectively. The indications for colorectal stenting, efficacy of the procedure in relieving the obstruction, complications and clinical outcome were analysed.

RESULTS

Ninety-nine patients had malignant disease and in three patients a benign cause of obstruction was demonstrated. All procedures were performed during normal working hours. Stenting was technically successful in 87 patients (85%). A single stent was placed in 80 patients. Seven patients required two stents. Of the successful cases, 67 had stents placed by fluoroscopy alone and 20 by a combined fluoroscopy/endoscopy procedure. Four percent had early complications (within 30 days) which included four perforations. There were late complications (over 30 days) in 9% which included five stent migrations, two blocked stents and one colovesical fistula. Ninety percent (n=76) of the successful patients needed no further radiological or surgical intervention later. Survival ranged from 14 days to 2 years.

CONCLUSION

Colorectal stenting when technically successful is an effective procedure for both preoperative and palliative decompression of colonic obstruction.

Anaesthetic implications of uterine artery embolisation in management of massive obstetric haemorrhage

The latest triennial report on maternal deaths has recommended the consideration of uterine artery embolisation in management of cases of massive obstetric haemorrhage. We have been using interventional radiology to manage both expected and unanticipated postpartum bleeding in our centre. Three case reports are presented to highlight the value of this technique and issues relating to the anaesthetic and postoperative management of these patients are discussed.

The use of non-prescription medicines by general practitioner attendees

PURPOSE

Against a background of increasing availability and use of non-prescription medicines, this study set out to explore: use of such medicines by patients seeing their general practitioner (GP); frequency of GP enquiry about such use; and frequency of recommendations to use a non-prescription medicine.

METHOD

Patients attending four general practices in Aberdeen, Scotland, completed separate questionnaires (before and after seeing their GP).

RESULTS

Some 461 individuals waiting to see their GP were invited to participate: 427 (93%) completed the pre-consultation questionnaire and 305 (71% of questionnaires issued) completed the post-consultation questionnaire. Almost half (45%) of all participants reported using non-prescription medicines in the 7 days prior to visiting their doctor; with 20% of the medicines purchased from non-pharmacy retail outlets. Thirteen per cent of participants were asked about their use of non-prescribed medicines by their GP. Eight per cent of participants were recommended to use a non-prescription medicine by their GP.

CONCLUSION

Although there was a high level of recent use of non-prescribed medicines by the general practice attenders, relatively few reported being asked about such use, or were recommended to use such medicines by their GP.

Mediastinal chest sump tubes following cardiac surgery: an unconventional method

The practice of using conventional mediastinal chest tubes (MCTs) connected to a closed collection device is commonplace in cardiovascular surgery care settings. The MCT collection device requires a closed system to maintain a negative intrathoracic pressure with the goal of preventing inadvertent trapping of air and blood within the mediastinal space. Despite the proposed integrity of the closed system, there is no guarantee that the suction's negative pressure will prevent cardiac tamponade. In addition, it has been postulated that the required negative intrathoracic suction may potentiate mediastinal tissue damage. This clinical paper will describe the use of multi-lumen MCTs open to atmosphere following surgical repair for congenital heart defects. It is postulated that open MCTs may potentially reduce the risks of cardiac tamponade and mediastinal tissue damage. Through case presentation, the mechanics of open MCTs, nursing care, and possible complications will be delineated.

Continuous venous hemodiafiltration with trisodium citrate anticoagulation in cardiac surgery patients

Despite advances in perioperative organ protection during cardiovascular surgery, acute renal failure remains a serious complication. The purpose of this clinical article is to describe the role of continuous renal replacement therapy (CRRT) in proactive maintenance of fluid and electrolyte balance and treatment of acute renal failure in patients following cardiovascular surgery. Implications for nursing practice, education, and future research will be delineated using a case study of a patient who required mechanical circulatory support and CRRT. The complexity of the patient's care was compounded by the need to alter conventional anticoagulation therapy to trisodium citrate.

Purification and characterization of pyruvate kinase from Schizosaccharomyces pombe: evidence for an unusual quaternary structure

Earlier attempts to purify and characterize nonrecombinant pyruvate kinase from Schizosaccharomyces pombe proved difficult due to problems associated with the instability of the protein. The enzyme has been overexpressed in Saccharomyces cerevisiae strain AH22, permitting studies to determine the conditions required to stabilize the enzyme during purification. Recombinant S. pombe pyruvate kinase was purified by a combination of ion-exchange chromatography and gel filtration. The purified enzyme showed sigmoidal kinetics with respect to PEP; in the presence of FBP, the kinetics were restored to Michaelis-Menten behavior. With respect to ADP, the Hill coefficient was not affected by FBP. Determination of the molecular mass of the purified enzyme by ultracentrifugation showed that it behaved as a dimer-tetramer system with a Kd of approximately 1 microM.

Effect of oestradiol and tamoxifen on the testosterone response in male rats to a single injection of hCG

A single s.c. injection of hCG (100 i.u.) produced a biphasic serum testosterone response in adult male rats, peaks being noted at 2 h (24 ng/ml) and 3 days (16 ng/ml). The levels fell to control during the intervening interval (8 ng/ml), although there were elevated levels of serum hCG. Maintenance of high oestradiol levels by a s.c. injection of 50 micrograms oestradiol benzoate given on Day 2 after the initial hCG injection failed to prolong the refractory period and the secondary peak of testosterone (16 ng/ml) occurred on Day 3. Administration of the antioestrogen, tamoxifen (2 mg or 3 micrograms), 24 h before or simultaneously with hCG did not prevent testicular refractoriness in vivo because serum testosterone levels still declined after 2 h to reach a nadir at 2 days. The basal in-vitro testosterone production by decapsulated testes from animals injected with hCG was enhanced at 2 h. Stimulation by hCG increased the amount of testosterone produced (X 1.5 that in controls). By 12 h basal production decreased and there was no further increment in testosterone in the presence of hCG. This refractoriness to further hCG stimulation prevailed until Day 3, but the total production of testosterone fell so that at 24 h and 2 days testes were producing basal amounts of testosterone. Testes recovered from refractoriness at 4 and 5 days, when basal and stimulated testosterone production were greater than in controls. Injection of 50 micrograms oestradiol benzoate at 2 days did not prolong the in-vitro refractory period and 2 mg or 3 micrograms tamoxifen had no effect on the in-vitro steroidogenic activity, since testes were still refractory to further hCG stimulation from 12 h to 3 days. The results of the present study do not support the hypothesis that oestradiol is involved in the hCG-induced refractoriness of the Leydig cell. The nadir between the peaks of serum testosterone in vivo corresponds to the period during which the testis is refractory to in-vitro stimulation by hCG.