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BACKGROUND Current treatment choices are based on generalized outcome data from clinical trials, but not all MM patients respond the same and a considerable percentage of them do not achieve a desirable treatment endpoint. Contradictory results based on the rate of descent of the monoclonal component (M-component) to predict long-term outcome have been published, but no to identify patients with insufficient response to a therapeutic regimen. The ability to identify treatment early on resistance could accelerate the introduction of another (and more effective) line of therapy. AIM Develop and validate a rule based on the rate of descent of the M-component, to predict the probability of disease resistance to reach a complete remission (CR) in MM patients. METHODS Three studies were conducted: exploratory, confirmatory, and clinical validation. A total of 87 patients treated between July 2014 and September 2018, were included for the first two. Patients who were unable to complete the planned treatment due to toxicity or comorbidities, and those treated for palliative purposes only, were excluded. A therapeutic regimen was considered to be effective if CR was achieved with it. Conversely, a therapeutic regimen was considered to be ineffective if disease progression was observed during treatment, or if CR was not achieved with it. The percentage of the daily decrease in the M-component achieved by each treatment cycle is calculated dividing the percentage of the decrease during the cycle by the number of days elapsed (n.nn% /day). Timing between measurement of the M-component do not differed more than 15% from the scheduled cycle time. In the exploratory study using the receiver operating characteristic (ROC) curve through SPSS v24, the ability to discriminate between effective and ineffective therapeutic regimen was investigated in 99 cycles, to identify the optimal cutoff, and to desing a rule; followed by a confirmatory study of the rule in 52 cycles different from those of the first study. A third clinical validation study was carried out with 62 patients, 31 with treatment guided by response speed rule (RSR-guided) and 31 not (unguided). RESULTS In the exploratory study it was observed that the area under the ROC curve was 0.971 (CI 95%: 0.93 - 1.00) (p 1.40% /day in a first cycle it does not indicate efficacy. In the confirmatory study it was observed for the RSR a sensitivity 100% (CI 95%: 92 - 100), specificity 100% (CI 95%: 66 - 100), reliability 100% (CI 95%: 93 - 100). In the clinical validation study the most common treatments in 1st, 2nd, and 3rd line were VBCMP/VBAD, VCD, and KRd for candidates, and VCD, Rd, DRd or KRd in non-candidates respectively. No significant differences were observed in the type of treatment used between RSR-guided and unguided patients. The median (months) to reach the CR in the RSR-guided patients was lower (8.5 vs 12.1 months; p = 0.003). RS-guided patients need fewer cycles to achieve CR (5.29 vs. 10.84; p = 0.002). The CR rate at 18 months was 94.3% (CI 95%: 84.1 - 100) and 74.2% (CI 95%: 58.4 - 90.0) for RSR-guided and unguided patients respectively, although in unguided patients the rate rose to 96.8% (CI 95%: 90.4 - 100.0) continuing treatment until 30 months. No significant differences were found in the number of lines for CR (1.96 vs 2.42; p = 0.054). CONCLUSIONS The Response Speed Rule (RSR), defined as a speed of M-component descent of ≤ 1.40% /day in two successive cycles, predicted with great accuracy the current ineffectiveness of a therapeutic regimen to deliver CR. During the clinical validation of this cutoff, it was shown that CR is achieved in less time and with fewer cycles using RSR. This is a simple metric that can be used broadly and accelerate the introduction of another (and more effective) line of therapy. Figure Disclosures No relevant conflicts of interest to declare.

Background: Assessing MRD has become a standard procedure in clinical trials to evaluate treatment efficacy. In accordance with its consistent prognostic value, the International Myeloma Working Group added MRD-negative criteria into response guidelines for its standardized use in clinical trials. That notwithstanding, the expectations for MRD as biomarker are to use it in routine clinical practice to help in treatment decisions, since in most clinical trials the therapeutic approach is defined upfront and does not vary according to patients' depth of response. However, the use of MRD in clinical practice is controversial and it remains unknown if tailoring treatment to achieve MRD-negativity is safe and improves patients' survival. Aim: Compare in clinical practice, outcome and tolerability of a treatment strategy tailored to achieve sustained undetectable MRD by NGF and imaging, as compared to conventional treatment approaches that are not modified according to patients' depth of response. Methods: This study was conducted in a single Hospital and included a total of 66 patients with newly-diagnosed MM from July 2014 to May 2019. All patients younger than 76 were prospectively included, whereas patients with high frailty score, severe senile dementia, other neoplasms, or with significant comorbidities in whom the therapeutic objective was only palliative care were excluded. In accordance to the local ethical committee and the Helsinki Declaration, all patients gave informed consent prior entering the study and were given the choice between the MRD and image driven (MRD-driven) and the conventional treatment (CT) approach. In the former, persistent MRD after the first-line of therapy was considered as treatment failure and patients received subsequent lines until achieving undetectable MRD by NGF and imaging (treatment endpoint). In the CT approach, subsequent lines of therapy were given upon progressive disease. The most commonly used first, second, and third line therapies in the MRD-driven approach were VBMCP/VBAD, VCD, and lenalidomide combinations, whereas in the CT cohort these were VCD for first-line, and lenalidomide combinations in second and third lines. Maintenance therapy (Interferon α2b + Prednisone for a year) was administered in 61% of patients treated according to the MRD-driven approach, and in 12% (bortezomib until progression) in the CT cohort. MRD was assessed in patients achieving complete remission using EuroFlow NGF, with a limit of detection of 2x10-6. Undetectable MRD by imaging was defined by negative PET/CT and by negative MRI of the spine and pelvis. Results: Of the 66 patients enrolled thus far, 49 were treated with the MRD-driven and 17 with the CT approach. There were no significant differences between groups regarding patients' age (median, 62 years), the Revised-ISS (37.5%, 53% and 37.5% with R-ISS-I, -II and -III) or the usage of HDT/ASCT (85% vs 76%; P>.05). Approximately 80% of patients treated with the MRD-driven approach achieved undetectable MRD at 30 months. The median time from start of treatment to undetectable MRD was 24 months, after a average of 2.2 lines of therapy. By contrast, only 1 (6%) patient treated with CT showed undetectable MRD after first line of therapy. With a median follow-up of 29 months, progression-free survival (PFS) rates at 30 months were 92% for patients treated with the MRD-driven vs 28% for the CT approach (hazard ratio 0.10 [0.04-0.30]; p Conclusions: We show that as compared to pre-specified therapies that are not modified according to patients' depth of response, an MRD-driven treatment approach reduces by 90% the risk of progression or death without increasing toxicity. These results support the use of undetectable MRD by NGF and imaging as treatment endpoint in routine clinical practice. Disclosures Paiva: Amgen, Bristol-Myers Squibb, Celgene, Janssen, Merck, Novartis, Roche, and Sanofi; unrestricted grants from Celgene, EngMab, Sanofi, and Takeda; and consultancy for Celgene, Janssen, and Sanofi: Consultancy, Honoraria, Research Funding, Speakers Bureau.