▪Background: HDT-ASCT with TBC conditioning has emerged as a common consolidation strategy for patients (pts) with relapsed/refractory (rel/ref) primary (PCNSL) or secondary (SCNSL) (Welch et al, Leuk & Lymph 2014). In a prospective study, chemosensitive PCNSL pts in first remission after induction with R-MPV (rituximab, MTX, procarbazine and vincristine) proceeding to HDT-ASCT with TBC conditioning, experienced an encouraging 2-year PFS and OS of 75% and 81%, respectively (Omuro et al, Blood, 2015). Three of these patients experienced transplant-related mortality (TRM, 11.5%), which appears greater than HDT-ASCT for other lymphomas. The purpose of this report is to correlate characteristic toxicities of TBC conditioning for CNSL to pre-HDT-ASCT clinical variables.Methods: The MSKCC IRB approved this retrospective chart review. Eligible pts (n=34) were ≥ 18 years of age with PCNSL or SCNSL that was chemosensitive to induction therapy after which they proceeded to HDT-ASCT conditioned with TBC between December 2006 and April 2015. All pts included were treated outside of prospective clinical trials. Clinically significant grade 3-5 non-hematologic toxicities per CTCAE 4.0 occurring in >20% of pts were recorded from the initiation of conditioning until 6 months post ASCT (Figure 1). Pre-HDT-ASCT variables for analysis include: age, gender, disease (PCNSL or SCNSL), Karnofsky performance status (KPS), hematopoietic cell transplant comorbidity index (HCT-CI), number of prior regimens, prior use of whole-brain radiotherapy (WBRT), and disease status prior to HDT-ASCT (CR/CRu or PR). We evaluated the association of these pre-HDT-ASCT characteristics with the number of clinically significant grade 3-5 non-hematologic toxicities (≥4 vs. <4) using FisherÕs exact test. We further estimated progression-free survival (PFS) and overall survival (OS) using Kaplan-Meier methods.Results: Thirty-three patients (97%) experienced ≥ 1 grade 3-5 non-hematologic toxicity. Febrile neutropenia (grade 3) occurred in 32 pts (94%). Of all pre-HDT-ASCT variables, only the number of prior regimens (>2) was significantly associated with incurring more grade 3-5 non-hematologic toxicities, p=0.04 (Table 1). With a median follow-up for survivors of 12 months (range, 1.5-86.2 months), PFS was 79% (95% CI, 65-96) and OS was 82% (95% CI, 68-98) at 1 year (Figures 2 and 3). During the follow-up period, there were 7 pt deaths: 4 died of disease, 2 died secondary to TRM (5.9%), and one died of a secondary malignancy (squamous cell carcinoma) 86.2 months after HDT-ASCT. There were no progression events beyond 12 months. In a limited subset analysis wherein n=22 had first dose bu pharmacokinetics evaluated, pre-HDT-ASCT variables were not associated with higher bu AUC levels, though 64% of these pts required a dose reduction.Conclusions: We reaffirmed that HDT-ASCT with TBC conditioning is effective consolidation for CNSL, but it is associated with more grade 3-5 non-hematologic toxicity in pts having had >2 prior regimens. Risk-adapted dose attenuation of TBC conditioning for this group of pts may mitigate observed toxicity.Table 1Association of Pre-ASCT Variables & Grade 3-5 Non-hematologic ToxicitiesNumber of Clinically Significant Grade 3-5 ToxicitiesPre-ASCT VariablesAll (N=34)Fewer than 4 (N=21)4 or more (N=13)p-valueAge0.71<6023 (68%)15 (71%)8 (62%)≥6011 (32%)6 (29%)5 (38%)Gender0.72Female13 (38%)9 (43%)4 (31%)Male21 (62%)12 (57%)9 (69%)Disease0.30PCNSL19 (56%)10 (48%)9 (69%)SCNSL15 (44%)11 (52%)4 (31%)KPS0.99≥8032 (94%)20 (95%)12 (92%)<802 (6%)1 (5%)1 (8%)BMT HCT CI0.99≤217 (50%)11 (52%)6 (46%)>217 (50%)10 (48%)7 (54%)Number of Prior Regimens0.04≤221 (62%)16 (76%)5 (38%)>213 (38%)5 (24%)8 (62%)WBRT0.17No28 (82%)19 (90%)9 (69%)Yes6 (18%)2 (10%)4 (31%)Disease state prior0.99CR/CRu29 (85%)18 (86%)11 (85%)PR5 (15%)3 (14%)2 (15%) [Display omitted] [Display omitted] [Display omitted] DisclosuresBhatt:Spectrum: Consultancy. Moskowitz:GSK: Research Funding; Merck: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding. Giralt:TAKEDA: Consultancy, Honoraria, Research Funding; JAZZ: Consultancy, Honoraria, Research Funding, Speakers Bureau; AMGEN: Consultancy, Research Funding; SANOFI: Consultancy, Honoraria, Research Funding; CELGENE: Consultancy, Honoraria, Research Funding.