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with eBPP at 4 UK centres. Results: From 2009, 103 patients were managed first line with either eBPP (n=51) or eBPDac (n=52) with median follow-up 37 months for eBPP and 10.4 months for eBPDac patients. Patients were well matched with no significant differences in age (median: 25), sex, stage (stage 3/4: 82%) and international prognostic score (IPS3+:71%). More patients treated with eBPDac received only 4 cycles of treatment (54% vs 10%; p=0.0007) reflecting recent HD18 trial data (1). In total, 74% patients achieved iPET Deauville score 2 or 3 and 98% patients achieved PET negative remission by end of treatment. Of eBPDac patients, 78% achieved iPET Deauville 2 or 3 which was statistically similar to the eBPP cohort (68%; p=0.344) and matched the 76% iPET D2/3 reported in HD18 (1). Of 103 patients, 102 are alive and 99 continue in first remission. Two eBPP patients have relapsed at 13 and 41 months. One eBPDac patient had primary refractory disease and one eBPDac patient died with bowel perforation. Toxicity was compared over the first 4 cycles. There was no difference in day 8 ALT between the two regimens although the mean day 8 neutrophil count was lower in eBPDac than eBPP patients (1.82 vs 2.35; p=0.056; G-CSF given day 9). There was a trend to fewer nonelective days of in-patient care for eBPDac compared with eBPP (mean: 2.8 vs 6.06; p=0.13), and eBPDac patients received fewer red cell transfusions during cycles 1 to 4 compared with eBPP patients (Mean 2.06 units vs 4.42 units; p=0.0009). Women aged < 35 with > 6 months post chemotherapy follow-up had a similar rate of return of menstrual cycles (eBPP: 20/21; eBPDac: 11/12), although eBPDac patients appeared to restart menstruation earlier post chemotherapy completion (mean: 3.91 months vs 8.65 months, p=0.0002). However, this could also reflect the higher mean chemotherapy cycle number completed by the eBPP women (5.86 vs 4.67; p=0.0005). The use of monthly Goserelin to suppress ovulation varied between centres. Conclusions: Accepting the limitations of a retrospective study, we suggest that substituting dacarbazine for procarbazine is unlikely to compromise the efficacy of eBPP and may have some toxicity benefits. As it is highly unlikely that this single drug substitution will ever be tested in a prospective trial, publishing real-world data from eBPDac patients is important. References 1. Borchmann P et al. Lancet. 2018;390:2790-2802