Ibrutinib at First Relapse for Mantle Cell Lymphoma: A United Kingdom Real World Analysis of Outcomes in 169 Patients

Background:

Ibrutinib has transformed the clinical approach to relapsed mantle cell lymphoma (MCL) with those receiving ibrutinib at first relapse obtaining the greatest benefit encouraging use earlier in the treatment algorithm (Rule et al, 2019). However, the general applicability of clinical trial findings is not established and concerns regarding ibrutinib tolerability persist, especially in non-trial populations enriched for frailer patients with multiple co-morbidities. In the United Kingdom, ibrutinib is funded as standard of care at first relapse. This study has analysed the clinical effectiveness and tolerability of this approach in a non-clinical trial real world population.

Method:

23 centres across the United Kingdom contributed data from consecutive patients treated with ibrutinib for MCL at first relapse. Patients received standard dose 560 mg OD, unless documented, and commenced treatment between August 2014 and April 2019. Response to therapy was defined as per Lugano classification (Cheson et al, 2014), although CR assessment by bone marrow biopsy was not always undertaken. Data was collected on baseline characteristics, including response to prior therapy, and MIPI at time of relapse. The study primary outcome was PFS. Predictors of progression were determined using univariate Cox regression.

Results:

169 patients were included in the study. Median age at start of ibrutinib was 72 years (range 33 to 97) and 122 (72.2%) were male. At diagnosis 13.5% had blastoid histology; 59.3% Ki67 ≥30%; 32.0% received cytarabine based induction and 27.8% HSCT consolidation; 11.2% received low intensity frontline therapy (i.e. not fit for R-CHOP) due to frailty. Median PFS following frontline therapy was 21.4 months (95% CI 14.6 to 28.3) and 52.1% progressed within 2 years. At start of ibrutinib 52.2% were MIPI high risk; 23.9% were ECOG 2 or higher and 2.4% had CNS involvement.

Overall response rate (ORR) to ibrutinib was 71.6% with 30.4% achieving CR/CRu. Estimated median PFS from start of ibrutinib was 16.5 months (95% CI 11.5 to 21.5) and estimated OS 23.9 months (95% CI 13.0 to 34.8), with median follow up 26 months. Median PFS for patients with early relapse to frontline therapy (progression of disease <2 years) was significantly shorter than those with more durable response (PFS 10.6 months vs. 20.6 months, HR 2.1, p=<0.001). Age ≥75 yrs and ECOG >1 were also negative predictors of PFS (see table 1 for univariate analysis). 10 patients (5.9%) received attenuated dose from start of therapy due to frailty and 20 patients (11.8%) underwent dose reductions while on therapy due to drug toxicity. Of 109 patients to discontinue ibrutinib 72 (66.1%) were due to progressive disease, 15 for consolidation alloHSCT (13.8%), 13 due to medical co-morbidities and unrelated death (11.9%), and 9 due to drug toxicity (8.3%), including 1 bleed. Only 5.3% of all patients stopped therapy due to drug toxicity.

Patients ≥80 yrs were more likely to stop therapy early for reasons other than progressive disease or alloHSCT (OR 2.92, p=0.02), but frailer patients who received low intensity frontline therapy also showed a trend for more durable response with second-line ibrutinib (PFS 10.0 months versus 4.0 months, p=0.36) justifying use in this patient group.

Conclusion:

This study population is enriched for several recognised adverse prognostic markers, including older age and poor performance status, which is likely to explain differences in PFS relative to clinical trial data. Despite these features response rates were similar, and it is notable that 46.7% of evaluable pts achieved longer PFS with ibrutinib than preceding front-line therapy. It is reassuring that the proportion of patients stopping ibrutinib due to toxicity was similar to trial data and bleeding events that required alterations to therapy were rare (3 cases, 1.8%).

Although ibrutinib represents a significant breakthrough with clear benefit to most patients the results also highlight that outcome for many remains poor. 40% of patients progressed within 1 year of starting ibrutinib and median OS post ibrutinib was only 3.6 months. 35.2% of patients died within 1 month of documented relapse suggesting many, predominantly older patients, were not fit for further therapy. Of the 53 pts surviving beyond 1 month median OS was 7.5 months and 21.9% lived beyond 1 year. Improved treatment strategies in the post-ibrutinib setting remains a priority.

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