Abstract Abstract 4031 Introduction: Excessive production of free light chains with affinity for uromodulin results in protein aggregates and toxic injury of distal renal tubules. The ensuing renal failure is a significant risk factor for infections, dependency on chronic hemodialysis and reduced survival. Management of this emergency includes rapid confirmation of the diagnosis and prompt installment of effective anti-myeloma therapy. Here, we assess the efficacy of lenalidomide-dexamethasone for treatment of patients with LC-ARF. Patients and Methods: 32 patients with LC-ARF as formerly defined (J. Clin. Oncol. 2010 20; 28(30):4635-41) have been enrolled so far. Age (median): 66 years (range: 46–87 years), Gender: male/female: 17/15. All patients presented with ISS stage III. 26 (81.3%) had de novo MM and 6 (18.8%) previously treated, but relapsing disease. Median GFR was 19.9 ml/min (range 6.1 – 37.2 ml/min). ECOG performance status was 0 in 9, I-II in 18 and III-IV in 5 patients, respectively. Lenalidomide was given from d 1–21 with dose adaptation according to GFR as suggested in the prescribing information. Dexamethasone 40 mg was administered on d 1–4, 9–12, 17–20 during cycle 1; thereafter 1x/week. Cycles were repeated q 4 weeks. Results: Presently, 23 patients are evaluable for response (completed ≥2 cycles and fully documented). The median follow-up is 7.7 months, median number of cycles is 9 (range 2–9). CR was achieved in 5 (21.7%), nCR in 1 (4%), VGPR in 2 (8%) and PR in 13 (52%) patients, MR in 1 (3%), respectively, yielding an ORR (CR+nCR+VGPR+PR) of 91.3% for evaluable patients and 65.6% for the ITT population. Median time to first myeloma response was 28 (range 27–63 days) and to best response was 113 days (34–304 days). The cumulative incidence of all patients with myeloma and renal responses are shown in figure 1. Median PFS and OS were 13.8 and 31.2 months respectively in the evaluable patients and 7.4 and 31.2 months in the ITT population. Renal response was assessed as formerly defined (J Clin Oncol. 2010 20; 28(30):4635-41). 4 patients achieved CRrenal, 8 PRrenal and 3 MRrenal, yielding an ORRrenal in 15 patients (65.2% of the evaluable and 46.9% of the ITT population). Median time to first renal response was 28 (range: 27–34) days, and to best renal response 119 days (34–304 days). 5 of 13 dialysis dependent patients became dialysis independent. Median GFR of evaluable patients increased from 15.2 (range 6.1 – 35.1 ml/min) at baseline to a median best GFR of 31.4 ml/min (range 11.3 – 103.2 ml/min). In the 5 patients with CR a significant increase in GFR (median 26.7 to 60.9 ml/min) and in the 16 patients with nCR/VGPR/PR an increase from 13.5 to 30.1 ml/min was observed. Full documentation of adverse events is presently available in 32 patients. 5 patients died within the first 2 months, 2 (8.7%) each due to infection and cardiac arrest and 1 (4.3%) with apoplexia. Grade 3/4 anemia, thrombopenia and leucopenia, were seen in 17 (53.1%), 9 (28.1%), and 5 (15.6%) patients, respectively. Other common grade 3/4 toxicities were infection/sepsis in 13 (40.6%), and cardiac dysfunction in 8 (25%) patients, respectively. Exanthema G3 was seen in 3 patients (9.3%), pulmonary embolism, macula edema and multiple stroke syndrome in 1 (3.1%), potassium deficiency G3/4 in 5 (15.6%), and oral candidiasis in 2 patients (6.3%) each. Conclusions: LD showed significant anti-myeloma activity with an overall myeloma response rate (CR-PR) of 91.3% in the evaluable of 65.5% in the ITT cohort. Renal responses (CRrenal-PRrenal) were observed in 65.2% and 46.9% patients, respectively. Time to first myeloma and first renal response was fast (28 days each). The LD regimen with the lenalidomide dose adjusted to GFR was well tolerated. Updated results will be presented. Disclosures: Ludwig: Janssen Cilag: Honoraria; Mundipharma: Honoraria; Celgene: Honoraria. Off Label Use: Lenalidomide was used of label in combination with dexamethasone in this phase II study in patients with acute light-chain induced renal failure.