The evidence for the use of single agent ibrutinib in relapsed/refractory mantle cell lymphoma (MCL) originates in a phase 3 study published in The Lancet in 2016r which advanced on a phase 2 study published in 2013 assessing ibrutinib use in relapsed/refractory mantle cell lymphoma.r Ibrutinib is an oral covalent inhibitor of Bruton’s tyrosine kinase, an essential enzyme in B cell receptor function. This open label, multicenter study, included 280 patients with relapsed or refractory mantle cell lymphoma who were randomized to receive either daily oral ibrutinib 560 mg or intravenous temsirolimus (175 mg on days 1, 8, and 15 of cycle 1; 75 mg on days 1, 8, and 15 of subsequent 21-day cycles). The primary endpoint was progression free survival while secondary endpoints included overall response rate (complete response and partial response), overall survival, 1-year survival rate, duration of response, time to next treatment, safety, pre-specified patient-reported outcomes, biomarkers and pharmacokinetics, and medical resource use rate. Median age was 68 years while median follow up was 20 months.r
A second study, published in NEJM in 2013 then updated in Blood in 2015 was a multicentre trial where ibrutinib was administered as a single agent to 111 patients with relapsed or refractory MCL.rr The primary endpoint was response rate with secondary endpoints of duration of response, progression free survival (PFS), overall survival (OS) and safety. The median age of the patients was 68 years and 86% had intermediate or high risk MCL based on clinical scores (simplified MIPI). The patients had received a median of 3 prior treatments (including bortezomib).r
Efficacy
Ibrutinib treatment resulted in a 57% reduction in the risk of disease progression or death compared with temsirolimus (HR 0·43 [95% CI 0·32–0·58]; p<0·0001, figure 1). The median progression-free survival was 14.6 months for the ibrutinib group and 6.2 months for the temsirolimus group. At 2 years, the progression-free survival rate is 41% in the ibrutinib group versus 7% in the temsirolimus group. Overall response rate was significantly higher in the ibrutinib group compared with the temsirolimus group (72% vs 40%, p <0.0001). Significantly, there was no benefit shown between the two arms in patients with the blastoid subtype, it should be noted however, that the sample size in this subgroup was small.r
The overall response rate in the phase 2 study by Wang et al. was 68% with 21% complete responses (CR) and 47% partial responses (PR) (see figure 2).r Prior treatment with bortezomib had no effect on response rate. A transient increase in the absolute lymphocyte count was observed in 34% of patients and typically resolved within a median of 8.0 weeks.r The median follow up in the initial paper was 15.3 monthsr and was extended to 26.7 months in the second publication.3 At the later follow up, the median treatment duration was reported as 8.3 months with 46% treated for >12 months and 22% for >24 months. The median PFS was 13 months and median OS was 22.5 months. The 2 year PFS was 31% and OS was 47% (see figure 3).r
Figure 1.

© The Lancet 2016
Figure 2.

© New England Journal of Medicine 2013
Figure 3.

© Blood 2015
Toxicity
The commonest non-haematological adverse events (AEs) seen in patients with MCL treated with ibrutinib were diarrhoea (56%), fatigue (50%), nausea (33%) and dyspnoea (32%) (see figure 4).r The majority of these events were of grade 1 or 2 only. Grade =3 haemorrhage did occur, with 2% of patients suffering subdural haematomas (all associated with trauma) and 2% experiencing haematuria. Atrial fibrillation (AF) occurred in 12 patients (11%) with grade 3 reported in 7 (6%), however treatment was not discontinued in any patient as a result of AF.r Haematological AEs included thrombocytopenia (22%), neutropenia (19%) and anaemia (18%) (see figure 4).r
The phase 3 study by Dreyling et al. showed a similar adverse effect profile though they did identify an increased number of secondary malignancies in the ibrutinib arm (figure 5).r These were predominantly non melanomatous skin cancers. It should be noted however, that when adjusted for length of exposure the risk of secondary malignancy was similar in both groups.r
Figure 4.

© Blood 2015
Figure 5.

© The Lancet 2016