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Somatic malignant transformation of germ cell tumours is a well-described but poorly understood phenomenon. It is characterized by differentiation of pluripotent teratoma cells into somatic tumour cells. Following malignant transformation, the most common histologies are sarcomas and primitive neuroectodermal tumours; however, other subtypes have been recognized including melanoma, leukaemia, and renal cell carcinoma. We report a case of a 38-year-old male who had recently completed treatment for a mediastinal germ cell tumour with teratomatous components. He presented several months after completion of chemotherapy with metastatic lesions in his spine and liver accompanied with severe pancytopenia. He was subsequently diagnosed with acute megakaryoblastic leukaemia (AMKL), and a biopsy of a liver lesion was consistent with metastatic melanoma. This case illustrates the simultaneous development of 2 rare malignant entities: mediastinal germ cell tumour-associated AMKL and somatic malignant transformation to melanoma. It also highlights the importance of close surveillance to detect these metastatic sequelae and the emerging role of tumour sequencing to establish targetable pathways.

Introduction The combination of rituximab & lenalidomide (R 2) is an established regimen for treatment of follicular lymphoma (FL), with efficacy reported in the first line and relapsed setting (Morchhauser NEJM 2018, Leonard JCO 2019). The inferior OS of patients who remain post-induction PET-CT positive (PET+ve) has also been demonstrated in both settings (Trotman Lancet Haem 2014, Lancet Oncol 2018, Ysebaert, ASH 2011). We sought to study the effect of R 2 in relapsed FL by examining its ability to convert to PET-negative (PET-ve) those patients who remain PET+ve after reinduction rituximab-chemotherapy. Methods This was a prospective, multicentre, Phase 2 study of patients with bulky Stage II, or Stage III-IV relapsed FL. Eligibility criteria were: at least stable disease on CT within 4-6 weeks of last cycle of re-induction rituximab-chemotherapy; ECOG ≤2; CrCL ³30mL/min; haemoglobin >80g/L, neutrophils >1.0 & platelets >75 x 10 9/L. Exclusion criteria were: histological transformation ≤12 months (mo); any interim-PET that was negative, and other malignancy ≤5 years. After enrolment pts underwent a centrally-reviewed PET within 8 weeks of D1 last cycle of re-induction rituximab-chemotherapy. Given the higher probability of further progression in the relapsed setting PET+ve was defined as a Deauville score (DS) 3-5. PET-ve patients were assigned rituximab maintenance q2mo for 2 years, and those remaining PET+ve were assigned R 2 to commence within 12 weeks. Lenalidomide schedule for R 2 pts was 10mg/d x 21 q28d, with dose modifications for tolerance, over a planned 2 years. Repeat PET scans were scheduled at 6 & 12 mo after starting R 2. The primary endpoint was the rate of conversion from postinduction PET+ve to PET-ve in evaluable patients 6 mo after commencing lenalidomide. Evaluable patients were defined as those receiving >63 days of Lenalidomide. Sample size calculations used a one-sided exact test for proportions, assuming a conversion rate of ³50% as worthy of further evaluation and ≤20% as unacceptable. Thus 16 evaluable patients were required to have 80% power with type I error of 5%. Secondary endpoints were PET conversion rates by baseline DS in the PET+ve, the toxicity & deliverability of R 2, and PFS & OS in both the PET+ve & PET-ve populations. Results Thirty-seven patients (pts) were recruited from Nov 2013 to Jan 2021 when the study was closed due to poor recruitment attributed to competing studies. Median (med) age was 67yrs (36-83); 58% male, med 2 (range 2-11) prior therapies incl. the recent rituximab-chemotherapy; FLIPI low risk (21%), intermediate risk (12%) high risk (67%). Eighteen of 37 (48.6%) pts were postinduction PET+ve. Med follow-up was 38 mo (0.8 - 76.4): 32 mo (0.8 - 76.4) in PET+ve and 42 mo (6.7 - 73.8) in PET-neg. Of the 18 PET+ve pts one was ineligible for R 2 due to reactivation of hepatitis B; 3 were not evaluable having not received >63 doses of lenalidomide due to progressive disease (PD). Thus 14/18 (78%) PET+ve pts were evaluable, of whom 5/14 (36%; 95% CI 11% - 61%) became PET-ve at 6-mo, thus not excluding a PET conversion rate of Of the 17 PET+ve pts starting lenalidomide, deliverability was limited by both disease progression and AEs: 3 failed to receive 3 cycles, 6 pts received 4-6, and 8 pts 7-24 cycles. Mean number of lenalidomide doses was 213 (SD 188). At least one AE was reported in 16/17 (94%), most commonly neutropenia (n=10, 59%, Gd4 24%). At least one SAE occurred in 9/17 (53%): infections 2, malignancy 2, cardiac disorders 2, musculoskeletal 2, other causes 3 pts. Conclusion The high PET+ve rate of 49% (DS 3-5) after rituximab-chemotherapy for relapsed FL suggests the need for consolidation therapy. However, R 2 did not achieve a sufficiently high PET-conversion rate to justify further study. The inferior outcome of patients who remain PET+ve after treatment of relapse highlights the importance of investigating novel approaches in this setting. Figure 1 Figure 1. Disclosures Trotman: TAKEDA: Research Funding; beigene: Research Funding; roche: Research Funding; BMS: Research Funding; PCYC: Research Funding; JANSSEN: Research Funding. Gandhi: janssen: Research Funding; novartis: Honoraria. Butcher: WriteSource: Current Employment, Other: Medical writing for Pharma companies. Not pertinent to this abstract for which author is study Statisticiam.

e20003 Background: A number of studies have demonstrated poorer outcomes for patients with cancer who live in rural/regional areas compared to metropolitan areas. There is conflicting information on the effect of rurality on outcomes of patients with multiple myeloma, and limited information regarding the cause of this discrepancy. Methods: Retrospective analysis of demographic, treatment and outcomes of 238 patients newly diagnosed with multiple myeloma between 2002-2019 in the Illawara Shoalhaven Local Health District. Results: Patients being treated in a regional cancer care centre had lower overall survival compared to those treated at a metropolitan cancer care centre (median OS = 63.6 months vs. 43.8 months, p=0.004), and a trend towards lower progression-free survival (median PFS = 24.7 months vs. 19.8 months, p=0.228) despite treatment by the same group of hematologists. There was a lower rate of autologous transplantation for patients treated at a regional cancer care centre compared to a metropolitan cancer care centre (36% vs. 18%, p=0.007). Conclusions: Survival differences between patients with multiple myeloma living in regional areas compared to metropolitan areas may be due to lower rates of autologous transplantation.

Aim High dose melphalan (HDM) and autologous stem cell transplantation (ASCT) retains a central role in the treatment of myeloma. The aim of this study was to determine whether HDM exposure (area under the concentration vs. time curve, AUC), is significantly associated with transplant outcomes. Methods Melphalan concentrations were measured in six to 11 plasma samples collected after HDM (median 192 mg m(-) (2) ) to determine melphalan AUC for a total of 114 patients. Binary logistic regression was used to assess whether melphalan AUC was associated with severe (≥ grade 3) oral mucositis. Multivariate Cox regression was used to assess whether melphalan AUC was significantly associated with time to progression, progression-free survival and overall survival (OS). Results Melphalan AUC ranged from 4.9 to 24.6 mg l(-1) h, median 12.84 mg l(-1) h. Melphalan AUC above the median was a risk factor for severe mucositis (HR 1.21, 95% CI 1.06, 1.38, P = 0.004) but was also associated with significantly improved overall survival (OS) (HR 0.40, 95% CI 0.20, 0.81, P = 0.001), with an estimated median survival of 8.50 years vs. 5.38 years for high vs. low AUC groups. Multivariate analysis did not identify melphalan AUC as being significantly associated with time to progression or progression-free survival. Conclusions This large scale pharmacodynamic analysis of HDM demonstrates that high melphalan exposure is associated with improved survival, with an acceptable increase in transplant toxicity. These results suggest studies targeting a higher AUC are warranted in patients undergoing HDM and ASCT for myeloma.

Introduction: 5'-Azacitidine (AZA), a DNA demethylating agent, is the primary drug for the treatment of high-risk Myelodysplastic Syndrome (MDS) and Chronic Myelomonocytic Leukaemia (CMML). Response is associated with improved survival. However, only half of patients respond, and these responses are rarely durable. We recently reported that primary AZA resistance is associated with a molecular signature of cell cycle quiescence within bone marrow (BM) hematopoietic progenitor cells (Unnikrishnan et al, Cell Reports, 20:572-585 (2017)). As DNA incorporation of the deoxyribonucleic form of AZA (5-aza-2′-deoxycytidine, DAC) occurs during DNA replication, cell cycle quiescence is predicted to lead to less DAC in DNA and concomitantly less DNA demethylation. We recently developed a quantitative multi-parameter assay, AZA-MS (Unnikrishnan, Vo et al, Leukemia 32:900-910 (2018)), to measure the intracellular dynamics of AZA in patients. Using AZA-MS, we reported data supporting the predicted resistance model. CC486 is an oral formulation of AZA. A 28-day cycle of CC486 involves 21 continuous days (21/28) versus the standard 7/28 subcutaneous (SC) injection AZA scheme. Whether levels of in vivo DAC incorporation into DNA during a cycle of CC486 are comparable with that of SC AZA is unknown. AZA-MS provides us with a unique opportunity to empirically assess the in vivo intracellular dynamics of SC versus oral AZA. Study Design and Methods: To directly assess in vivo DAC incorporation and concomitant DNA demethylation with SC AZA and CC486 in the same patient, we initiated a phase II clinical trial (NCT03493646; Fig A). MDS (IPSS; intermediate-2 or high-risk), CMML (bone marrow [BM] blasts 10-29%) and AML (20-30%) patients were recruited for six cycles of SC AZA (75mg/m^2/day for 7/28 days) followed by six cycles of CC486 (100mg bid for 21/28 days in C7-C8 and 150mg bid for 21/28 in C9-C12). Clinical response was assessed at the end of C6 and C12 using International Working Group criteria. Clinical responders and non-responders to SC AZA at C6 received CC486 from C7 onwards. From each patient, 36 peripheral blood (PB) samples and five BM samples were collected over the study period. DNA, RNA and intracellular fractions were isolated from the PB MNCs, for intracellular DAC/AZA measurements by AZA-MS (primary endpoint; Fig A). BM MNCs were utilised for AZA-MS as well as flow cytometry-based cell cycle measurements (secondary endpoint). Results: 31 of 42 consented patients have commenced treatment since trial opening (Fig B-C). We applied the AZA-MS assay on the longitudinal PB and BM samples collected from the seven patients who had completed six months AZA and commenced CC486 as at 26th June 2019 (Fig D). DAC incorporation into DNA and DNA methylation levels were quantified within the same cells, in addition to measuring other parameters (Fig E). As represented by patient 61213-005 (Fig F) who had a complete response (CR) at cycle 6, after 7 days of injection AZA we observed robust incorporation of DAC within PB MNCs (left panel, Fig F) together with concomitant DNA demethylation (right panel, Fig F). DAC levels diminished upon cessation of AZA within a cycle, with corresponding increases in DNA methylation. There were quantitatively higher levels of DAC incorporated in DNA during SC AZA cycles versus CC486. The trend observed is also appreciated from 2.3x higher area under the curve (AUC) measurements in 61213-005 during the SC AZA cycle. DAC incorporation was higher at C9/10 (CC486 150mg bid 21/28) than at C7/8 (CC486 100mg bid 21/28) without appreciable changes in DNA demethylation. During SC AZA cycles, higher DAC levels (top panel, Fig G) and greater DNA methylation (lower panel, Fig G) were seen in the BM MNCs. In a non-responding patient at cycle 6 (61290-002, SD), we saw less DAC incorporation and DNA demethylation (Fig H). We also observed a positive correlation between baseline proportions of cycling BM cells (LIN-CD34+CD38+) and the amount of DAC incorporated in BM MNCs at C1 day 8 (Fig I). Conclusion: AZA-MS can be used to reliably measure in vivo DAC incorporation and concomitant DNA demethylation in PB MNCs and inform appropriate CC486 dosing. Figure Disclosures Unnikrishnan: Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Fong:Astellas: Consultancy; Novartis: Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; Amgen: Consultancy, Research Funding, Speakers Bureau. Roncolato:St. George Hospital: Employment. Enjeti:Roche: Honoraria, Speakers Bureau; Bayer and Sanofi: Honoraria, Speakers Bureau; Astellas: Consultancy; Novartis: Consultancy; Abbvie: Consultancy. Hertzberg:BMS: Membership on an entity's Board of Directors or advisory committees; F. Hoffmann-La Roche Ltd: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees. Polizzotto:Janssen: Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Merck: Research Funding; ViiV: Research Funding. Pimanda:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • There has been one previous population pharmacokinetic analysis of total melphalan given as a short infusion in 84 adults (mixed diagnoses) and creatinine clearance and body size were found to be important determinants of total melphalan clearance. Dose and exposure to total melphalan were found to correlate with the development of mucositis. WHAT THIS STUDY ADDS • This is the largest population pharmacokinetic study on melphalan conducted to date. It is the first conducted in a uniform patient population (patients with multiple myeloma) and the first in which both total and unbound melphalan pharmacokinetics are examined. Factors found to be important determinants of total and unbound plasma clearance of melphalan were creatinine clearance, fat free mass and haematocrit. Haematocrit has not previously been identified as an influential covariate in any previous study. The importance of total and unbound melphalan exposure on transplant outcome was demonstrated by preliminary pharmacodynamic results showing significant associations with melphalan-related toxicity. A preliminary analysis of the association with disease response showed promising trends, but will be examined in more detail with longer follow-up of the whole cohort. AIMS To i) investigate the pharmacokinetics of total and unbound plasma melphalan using a population approach, ii) identify clinical factors that affect melphalan disposition and iii) evaluate the role of melphalan exposure in melphalan-related toxicity and disease response. METHODS Population pharmacokinetic modelling (using NONMEM) was performed with total and unbound concentration–time data from 100 patients (36–73 years) who had received a median 192 mg m−2 melphalan dose. Model derived estimates of total and unbound melphalan exposure (AUC) in patients with serious melphalan toxicity and those who had a good disease response (≥90% decrease in paraprotein concentrations) were compared using the Mann-Whitney test. RESULTS A two compartment model generated population mean estimates for total and unbound melphalan clearance (CL) of 27.8 and 128 l h−1, respectively. Estimated creatinine clearance, fat free mass and haematocrit were important determinants of total and unbound CL, reducing the inter-individual variability in total CL from 34% to 27% and in unbound CL from 42% to 30%. Total AUC (range 4.9–24.4 mg l−1 h) and unbound AUC (range 1.0–6.5 mg l−1 h) were significantly higher in patients who had oral mucositis (≥grade 3) and long hospital admissions (P < 0.01). Patients who responded well had significantly higher unbound AUC (median 3.2 vs. 2.8 mg l−1 h, P < 0.05) when assessed from diagnosis to post-melphalan and higher total AUC (median 21.3 vs. 13.4 mg l−1 h, P= 0.06), when assessed from pre- to post-melphalan. CONCLUSIONS Creatinine clearance, fat free mass and haematocrit influence total and unbound melphalan plasma clearance. Melphalan exposure is related to melphalan toxicity while the association with efficacy shows promising trends that will be studied further.

Autologous stem cell transplantation (ASCT) has a well-established role in the treatment of haematological malignancies. Stem cells are commonly collected following salvage chemotherapy although there may be advantages in collecting earlier in the disease course. A ’rainy day’ harvest (RDH) refers to the collection of autologous haemopoietic stem cells for long-term storage. Although there are few data to support RDH, there is increasing evidence that such harvests are being carried out, creating storage pressures in stem cell laboratories across New South Wales. The Bone Marrow Transplant Network New South Wales conducted a three-staged exercise to develop consensus-based RDH guidelines. Using available evidence, guidelines were developed supporting RDH for specific patients with acute and chronic myeloid leukaemias, follicular and other lymphomas, and multiple myeloma. Physician agreement with these disease-specific guidelines ranged between 58 and 100%. These consensus guidelines will improve equity of access to appropriate RDH and assist the planning of future storage requirements in New South Wales.

Introduction and aims: High-dose melphalan (HDM) is the commonest conditioning regimen used in autologous transplantation for multiple myeloma (MM), with >10,000 transplants performed annually. The standard dosing algorithm of 200mg/m2, with reduction to 140mg/m2 for renal impairment, has been based upon empiric dose selection, rather than pharmacokinetic (PK) and pharmacodynamic (PD) studies. We have previously examined PK and clinical outcome in 114 patients receiving HDM and shown that exposure (area under the concentration versus time curve: AUC) above the median (12.8 mg/L.h) was associated with increases in ≥ grade 3 mucositis (HR 1.2, p< 0.005), and a median overall survival of 8.5 years vs. 5.4 years for AUC below the median (HR 0.40, p < 0.001) [1]. The aims of this pilot study were to (1) test the feasibility of real-time PK in patients with MM and (2) evaluate whether a test dose reliably predicted exposure to a full dose. Methods: Thirty three patients (age range: 35 to 71 years) scheduled to receive HDM followed by ASCT were recruited from six Australian hospitals situated within 16-860km from the PK laboratory. A test dose (20 mg/m2) was administered one to three days prior to the remaining 180 mg/m2, n=29, or another dose (n = 4, 186- 200mg/m2) chosen by the treating physician. Melphalan infusion duration ranged from 9 to 36 min for the test dose and from 15 to 45 min for the remaining dose. Blood samples were collected after both doses at: 5 min, 15 min, 30 min, 40 min, 1.25 h and 2.5 h after completion of the infusion, stored immediately on ice and centrifuged within 40 minutes at 3000 rpm for 10 minutes at 4o C to collect plasma, then stored at -40°C until transported on dry ice. Melphalan concentrations were determined by HPLC with UV detection. Test dose AUC was calculated using the trapezoidal rule (Kinetica software) and used to predict what the AUC would be for the 180mg/m2 (or modified) dose, assuming linear PK. Percent deviation of actual-from-predicted AUC was calculated as % deviation = (actual AUC - predicted AUC) / predicted AUC*100. Comparison of % deviation between the first patient recruited at each institution and the remaining patients was performed using the Mann-Whitney test. Results: The predicted and actual melphalan AUC values for all 33 patients are charted (Figure 1). AUC values following the test dose were median (range): 1.34 (0.83-1.88 mg/L.h). Predicted AUC values (adjusted for subsequent dose) were median (range): 11.8 (8.3-15.8) mg/L.h, whilst actual values were 10.5 (6.3-16.0) mg/L.h. Median % deviation of actual from predicted values was -8%, (range -43 to 11%), with predictions for 23 patients (70%), being within ± 15%. The median % deviation for the first patient in each centre was -22.1%, and for subsequent patients was -7%, (p=0.046), for whom 21/27 (78%) had full dose AUC values within ± 15%. Conclusions: Test-dose PK predictions of melphalan exposure were accurate to within ± 15% for 70% of patients in this pilot study. The significantly improved AUC predictions with subsequent dosing suggest that meticulous care is required in dose administration and blood sampling. Other factors such as duration of infusion, concomitant medications and renal function are being examined in a larger cohort to identify any impact on melphalan exposure and subsequently whether PK directed dosing of HDM to achieve a desirable AUC is sufficiently reliable to implement for patients undergoing ASCT. [1] Shaw PJ et al. Biol Blood Marrow Transplant (2012): 18 (2), S207 Abs13. Figure 1. Figure 1. Disclosures Grigg: Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees; Merck: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Abstract 1749 Poster Board I-775 Introduction Both thalidomide (Thal) and 5-azacitidine (Vidaza; AZA) have single-agent activity in patients (pts) with myelodysplastic syndromes (MDS), but there is limited experience with the combination. The addition of Thal to AZA may improve efficacy, but tolerability of the combination may be limited by side-effects. Patients and Methods This analysis included all evaluable pts on the Ph I/II Australasian Leukaemia and Lymphoma group (ALLG) MDS3 study of Thal and AZA. Pts were eligible if they had any FAB subtype of MDS; those with RA and RARS also required clinically significant cytopenias. Pts were excluded if they had previously received Thal or its derivatives or any demethylating agent. All pts were treated with Thal 50mg/d for the first 28d increasing to 100mg/d for a max of 12 Mo treatment and AZA 75mg/m2/d x7d every 28d until progression or prohibitive toxicity. The protocol specified dose delays or reductions for treatment-related toxicities. Results A total of 80 pts have been enrolled, with 41 treated between 7/08 – 7/09 currently evaluable. Median age is 68.5y (42-81) with 66% male. FAB MDS category was RA 15%, RARS 10%, RAEB 46%, RAEB-t 10% and CMML 17% with IPSS low 12%, intermed-1 37%, intermed-2 34% and high 12%. Median baseline Hb 88g/L (71-127), ANC 1.91×10 9/L (0.06-87.65) and platelets 75 ×10 9/L (10-399). Median time post diagnosis was 9 Mo. Seventeen pts (41%) remain on treatment with AZA alone (n=3) or both agents (n=14) with a median follow-up of 208d (60-297d). For those still on Thal and AZA median exposure to Thal is 209d (60-297d), with a median 7 cycles of AZA (2-9). For those 27 ceased Thal median exposure was 49d (17-220d) and of 24 ceasing AZA, median number cycles was 2 (1-8). Of 27 pts ceasing one (n=3) or both (n=24) agents; 7 withdrew consent, 3 at investigator decision, 4 for toxicity, 6 progressive disease, 1 lack of efficacy, 2 death (1 respiratory failure in setting of PD and WCC>300, 1 sepsis) and 4 unknown. There were 3 additional deaths within 28d of ceasing study therapy (all with PD); 2 due to sepsis and 1 intracranial haemorrhage. No pt experienced peripheral neuropathy Gr3 or worse. During cycle 1 of the first 40 consecutive patients on treatment, there were 18 episodes of Gr3+ non-haematologic toxicity in 13 patients; this was more likely in those with ECOG 2 (67% v 26%, p=0.053), age>65y (39% v 19%, p=0.175) and baseline ANC'0.5 (75% v 21%, p=0.008). Most of these events were infection related (a recognised risk of underlying MDS and of AZA alone); others occurred on only one occasion each (syncope, postop hemorrhage, respiratory disorder, renal failure, abdominal pain, pain, thrombosis and hypokalemia). Conclusions The combination of Thal 50-100mg/d and standard dose AZA is feasible without unexpected toxicity. Infections are common in the first cycle, particularly in pts with baseline neutropenia or impaired performance status. An updated toxicity analysis will be presented. Disclosures Kenealy: Celgene Pty Ltd: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Seymour:Celgene Pty Ltd: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Mills:Celgene Pty Ltd: Honoraria, Membership on an entity's Board of Directors or advisory committees. Szer:Celgene Pty Ltd: Honoraria, Speakers Bureau.

Abstract 1979 Introduction and aims: High-dose melphalan (HDM) for myeloma is the commonest conditioning regimen used in autologous transplantation with >10,000 transplants performed world-wide each year. Despite evidence of a dose-response effect, the standard dosing algorithm of 200mg/m2, with reduction to 140mg/m2 for renal impairment, has been based upon small comparative and observational studies, and not from pharmacokinetic analysis. We have examined the pharmacokinetics and clinical outcome of 115 patients receiving HDM and shown that exposure (area under the concentration versus time curve, AUC) above the median (12.85 mg/L.h) is associated with increased mucositis (HR 1.2, p < 0.005), but improved time to progression (TTP) (HR 0.35, p Methods: For the 115 myeloma patients, (median age 58 (35 –73) years) enrolled in this study between 2004 and 2010 [1], the median follow up is now 3.7 years. The Mann Whitney test was the used to compare the following characteristics between patients with low ( Results: In the total population, patients with low and high melphalan AUC did not differ significantly in weight, BMI, mg/m2 melphalan dose or % dose decrease. However, patients with a low AUC had significantly better renal function: (CrCl, median (interquartile range) 97 (79–112) vs. 77 (58–90) ml/min/70 kg (p Conclusions: This pharmacokinetic study of HDM was conducted in the modern era characterised by both the impact of myeloma biotherapies and an increasing prevalence of obesity. Obese patients obtained comparable drug exposure and clinical outcomes as normal weight patients despite receiving a significantly lower mg/m2 dose of melphalan. Regardless of BMI, patients with low exposure to HDM had significantly better renal function, consistent with renal excretion being an important elimination pathway for melphalan. Given the significantly prolonged survival in patients with higher exposure to melphalan a dose increase may be appropriate in patients with excellent renal function. Clinical trials of pharmacokinetic based targeting to safely achieve this higher exposure, in lieu of a mg/m2 based dosing are now warranted. Disclosures: No relevant conflicts of interest to declare.