Analysis of secretomes critically underpins the capacity to understand the mechanisms determining interactions between cells and between cells and their environment. In the context of cancer cell micro-environments, the relevant interactions are recognized to be an important determinant of tumor progression. Global proteomic analyses of secretomes are often performed at a single time point and frequently identify both classical secreted proteins (possessing an N-terminal signal sequence), as well as many intracellular proteins, the release of which is of uncertain biological significance. Here, we describe a mass spectrometry-based method for stable isotope dynamic labeling of secretomes (SIDLS) that, by dynamic SILAC, discriminates the secretion kinetics of classical secretory proteins and intracellular proteins released from cancer and stromal cells in culture. SIDLS is a robust classifier of the different cellular origins of proteins within the secretome and should be broadly applicable to nonproliferating cells and cells grown in short term culture.

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e14522 Background: Corticosteroids are commonly used in neuro-oncology both in the perioperative setting and with chemotherapy and radiotherapy to manage cancer and treatment-associated cerebral oedema and neurological deficits. Corticosteroids are associated with significant morbidity. We sought to identify primary brain tumour patients affected by steroid complications within our centre, the repercussions on their treatment and whether these consequences are avoidable. Methods: This retrospective study curated the last 50 primary brain tumour patients treated radically and therefore at risk of long term steroid use between November 2018 and August 2019. Patient demographics, tumour and treatment type, as well as diabetic and steroid history were collected. A second cohort of primary brain patients undergoing radical radiotherapy were recruited between November 2019 and January 2020. HbA1c blood tests were performed and NICE guidelines used for HbA1c diagnostic criteria with referral to diabetic services and outcomes recorded. Results: Tumour types ranged from Glioblastoma (36%), meningioma (32%), oligodendroglioma (16%), astrocytoma (14%) and hemangioblastoma (2%). 12 (24%) had a known diabetes diagnosis. Forty-two (84%) had an operation (biopsy (30%), partial (18%) or full debulking (16%). 82% of patients were exposed to dexamethasone at some point during their neurosurgical or oncological treatment. Initial doses varied but 36% were placed on 8mg twice daily. Steroid-induced hyperglycaemia occurred in 8 (16% of the cohort) with admission to hospital as a consequence in half of these cases, of whom two were newly diagnosed diabetes patients. HbA1c testing prior to or during treatment occurred in 16 (32%) patients. In the second cohort, All 15 patients (100%) had HbA1c testing with 5 (33%) patients diagnosed with diabetes or at risk of diabetes. Diabetic team advice was sought and recommended blood glucose testing in all these patients with oral hypoglycaemic and/or insulin dose modification in 3 (60%). There were no hyperglycaemic recordings or subsequent admissions to hospital in this cohort. Conclusions: We therefore recommend HbA1c testing and early diabetic team involvement in all primary brain tumour patients receiving radical radiotherapy.

AimTo undertake a survey of UK paediatric endocrinologists to assess the current practice for sex steroid priming prior to growth hormone stimulation tests (GHST).MethodsAn online questionnaire was sent to Paediatric Endocrinology centres in the UK assessing their current practice of priming for GHST.Results26 responses were received from 24 centres with 18/24 (67%) of responses from tertiary endocrine centres and 8/24 (33%) responses from district general hospitals. The agents used for growth hormone stimulation included insulin 15/26 (58%), clonidine 5/26 (19%), arginine 14/26 (54%), glucagon 24/26 (92%) and GnRH/arginine 2/26 (8%). 13/26 (50%) used the cut-off of 6.7ug/l for diagnosis. 85% (22/26) use sex steroid priming. The regimes used for priming are shown in Table 1. Some respondents used more than one regime.Abstract G434 Table 1The priming regimes used by survey respondents for boys and girlsPriming Regime [Time (days) given before GHST]Number using regime for priming boysNumber using regime for priming girls100 mg testosterone IM (8–10)10100 mg testosterone IM (5–7)20100 mg testosterone IM (2–4)3050 mg testosterone (5–7)30Diethylstilboestrol 1mg twice a day orally (2)1012Ethinyloestradiol 10 mcg once daily (3)14Ethinyloestradiol 20 mcg once (3)33Other44The criteria to prime boys was pre-pubertal with a bone age (BA) >10 years (8/22 (36%)) or chronological age (CA) of >10years (4/22 (18%)). 4 (18%) used either BA or CA and 6/22 (27%) had a practice different to this. The criteria to prime girls was pre-pubertal with a BA >10 years (8/22 (36%)) or CA >10 years (5/22 (23%)). 1/22 (5%) used either BA or CA and 8/22 (36%) had practice different to this.ConclusionSex steroid priming is still a controversial area of paediatric endocrinology and there is no clear consensus on how this is undertaken. There appears to be a wide variation in practice in terms of the selection of patients and the drugs and methods used for priming. A consensus guideline on appropriate sex steroid priming prior to GHST will minimise the variation in the diagnosis of growth hormone deficiency.