Next-generation sequencing has revealed recurring somatic mutations in Waldenström macroglobulinemia (WM), including MYD88 (95%-97%), CXCR4 (30%-40%), ARID1A (17%), and CD79B (8%-15%). Deletions involving chromosome 6q are common in patients with mutated MYD88 and include genes that modulate NFKB, BCL2, Bruton tyrosine kinase (BTK), and apoptosis. Patients with wild-type MYD88 WM show an increased risk of transformation and death and exhibit many mutations found in diffuse large B-cell lymphoma. The discovery of MYD88 and CXCR4 mutations in WM has facilitated rational drug development, including the development of BTK and CXCR4 inhibitors. Responses to many agents commonly used to treat WM, including the BTK inhibitor ibrutinib, are affected by MYD88 and/or CXCR4 mutation status. The mutation status of both MYD88 and CXCR4 can be used for a precision-guided treatment approach to WM.

Purpose Ibrutinib is active in previously treated Waldenström macroglobulinemia (WM). MYD88 mutations ( MYD88) and CXCR4 mutations ( CXCR4) affect ibrutinib response. We report on a prospective study of ibrutinib monotherapy in symptomatic, untreated patients with WM, and the effect of CXCR4 status on outcome. Patients and Methods Symptomatic, treatment-naïve patients with WM were eligible. Ibrutinib (420 mg) was administered daily until progression or unacceptable toxicity. All tumors were genotyped for MYD88 and CXCR4. Results A total of 30 patients with WM received ibrutinib. All carried MYD88, and 14 (47%) carried a CXCR4. After ibrutinib treatment, median serum IgM levels declined from 4,370 to 1,513 mg/dL, bone marrow involvement declined from 65% to 20%, and hemoglobin level rose from 10.3 to 13.9 g/dL ( P < .001 for all comparisons). Overall (minor or more than minor) and major (partial or greater than partial) responses for all patients were 100% and 83%, respectively. Rates of major (94% v 71%) and very good partial (31 v 7%) responses were higher and time to major responses more rapid (1.8 v 7.3 months; P = 0.01) in patients with wild-type CXCR4 versus those with CXCR4, respectively. With a median follow-up of 14.6 months, disease in two patients (both with CXCR4) progressed. The 18-month, estimated progression-free survival is 92% (95% CI, 73% to 98%). All patients are alive. Grade 2/3 treatment-related toxicities in > 5% of patients included arthralgia (7%), bruising (7%), neutropenia (7%), upper respiratory tract infection (7%), urinary tract infection (7%), atrial fibrillation (10%), and hypertension (13%). There were no grade 4 or unexpected toxicities. Conclusion Ibrutinib is highly active, produces durable responses, and is safe as primary therapy in patients with symptomatic WM. CXCR4 status affects responses to ibrutinib.

MYD88 mutations are present in 95% of Waldenstrom Macroglobulinaemia (WM) patients, and support diagnostic discrimination from other IgM-secreting B-cell malignancies. Diagnostic discrimination can be difficult among suspected wild-type MYD88 (MYD88 ) WM cases. We systematically reviewed the clinical, pathological and laboratory studies for 64 suspected MYD88 WM patients. World Health Organization and WM consensus guidelines were used to establish clinicopathological diagnosis. Up to 30% of suspected MYD88 WM cases had an alternative clinicopathological diagnosis, including IgM multiple myeloma. The estimated 10-year survival was 73% (95% confidence interval [CI] 52-86%) for MYD88 versus 90% (95% CI 82-95%) for mutated (MYD88 ) WM patients (Log-rank P < 0·001). Multivariate analysis only showed MYD88 mutation status (P < 0·001) as a significant determinant for overall survival. Diffuse large B-cell lymphoma (DLBCL) was diagnosed in 7 (15·2%) and 2 (0·76%) of MYD88 and MYD88 patients, respectively (Odds ratio 23·3; 95% CI 4·2-233·8; P < 0·001). Overall survival was shorter among MYD88 patients with an associated DLBCL event (Log-rank P = 0·08). The findings show that among suspected MYD88 WM cases, an alternative clinicopathological diagnosis is common and can impact clinical care. WM patients with MYD88 disease have a high incidence of associated DLBCL events and significantly shorter survival versus those with MYD88 disease.

Activating MYD88 mutations are present in 95% of Waldenström macroglobulinemia (WM) patients, and trigger NF-κB through BTK and IRAK. The BTK inhibitor ibrutinib is active in MYD88-mutated (MYD88MUT) WM patients, but shows lower activity in MYD88 wild-type (MYD88WT) disease. MYD88WT patients also show shorter overall survival, and increased risk of disease transformation in some series. The genomic basis for these findings remains to be clarified. We performed whole exome and transcriptome sequencing of sorted tumor samples from 18 MYD88WT patients and compared findings with WM patients with MYD88MUT disease. We identified somatic mutations predicted to activate NF-κB (TBL1XR1, PTPN13, MALT1, BCL10, NFKB2, NFKBIB, NFKBIZ, and UDRL1F), impart epigenomic dysregulation (KMT2D, KMT2C, and KDM6A), or impair DNA damage repair (TP53, ATM, and TRRAP). Predicted NF-κB activating mutations were downstream of BTK and IRAK, and many overlapped with somatic mutations found in diffuse large B-cell lymphoma. A distinctive transcriptional profile in MYD88WT WM was identified, although most differentially expressed genes overlapped with MYD88MUT WM consistent with the many clinical and morphological characteristics that are shared by these WM subgroups. Overall survival was adversely affected by mutations in DNA damage response in MYD88WT WM patients. The findings depict genomic and transcriptional events associated with MYD88WT WM and provide mechanistic insights for disease transformation, decreased ibrutinib activity, and novel drug approaches for this population.

Summary Ibrutinib is associated with response rate of 90% and median progression‐free survival (PFS) in excess of 5 years in Waldenström macroglobulinaemia (WM) patients. CXCR4 mutations are detected in 30–40% of patients with WM and associate with lower rates of response and shorter PFS to ibrutinib therapy. Both frameshift (CXCR4FS) and nonsense (CXCR4NS) CXCR4 mutations have been described. The impact of these mutations on outcomes to ibrutinib have not been evaluated in WM patients. We studied consecutive patients with a diagnosis of WM, on ibrutinib therapy, for the presence of CXCR4FS and CXCR4NS mutations and evaluated the differences in response and PFS between groups. Of 180 patients, 68 patients (38%) had CXCR4 mutations; 49 (27%) had CXCR4NS and 19 (11%) had CXCR4FS mutations. In multivariate models, patients with CXCR4NS had lower odds of major response (Odds ratio 0·25, 95% confidence interval [CI] 0·12–0·53; P < 0·001) and worse PFS (Hazard ratio 4·02, 95% CI 1·95–8·26; P < 0·001) than patients without CXCR4 mutations. CXCR4FS was not associated with worse major response or PFS rates than patients without CXCR4 mutations. Our results suggest different response and PFS rates to ibrutinib for WM patients with CXCR4NS and CXCR4FS, and advocate in favour of CXCR4 mutational testing as well as CXCR4‐directed therapy.

Acquired ibrutinib resistance due to BTK mutations occurs in B-cell malignancies, including those with MYD88 mutations. BTK mutations are usually subclonal, and their relevance to clinical progression remains unclear. Moreover, the signaling pathways that promote ibrutinib resistance remain to be clarified. We therefore engineered BTK and BTK expressing MYD88-mutated Waldenström macroglobulinemia (WM) and activated B-cell (ABC) diffuse large B-cell lymphoma (DLBCL) cells and observed reactivation of BTK-PLCγ2-ERK1/2 signaling in the presence of ibrutinib in only the former. Use of ERK1/2 inhibitors triggered apoptosis in BTK-expressing cells and showed synergistic cytotoxicity with ibrutinib. ERK1/2 reactivation in ibrutinib-treated BTK cells was accompanied by release of many prosurvival and inflammatory cytokines, including interleukin-6 (IL-6) and IL-10 that were also blocked by ERK1/2 inhibition. To clarify if cytokine release by ibrutinib-treated BTK cells could protect BTK MYD88-mutated malignant cells, we used a Transwell coculture system and showed that nontransduced BTK MYD88-mutated WM or ABC DLBCL cells were rescued from ibrutinib-induced killing when cocultured with BTK but not their BTK-expressing counterparts. Use of IL-6 and/or IL-10 blocking antibodies abolished the protective effect conferred on nontransduced BTK by coculture with BTK expressing WM or ABC DLBCL cell counterparts. Rebound of IL-6 and IL-10 serum levels also accompanied disease progression in WM patients with acquired BTK mutations. Our findings show that the BTK mutation drives ibrutinib resistance in MYD88-mutated WM and ABC DLBCL cells through reactivation of ERK1/2 and can confer a protective effect on BTK cells through a paracrine mechanism.

Herein, we present the final report of a single-center, prospective phase II study evaluating ibrutinib 420 mg once daily in 30 treatment-naive patients with Waldenstrom macroglobulinemia (WM). The present study is registered with ClinicalTrials.Gov (NCT02604511). With a median follow-up of 50 months, the overall, major, and VGPR response rates were 100%, 87%, and 30%. The VGPR rate was numerically but not significantly lower in patients with than without CXCR4 mutations (14% vs. 44%; p = 0.09). The median time to a minor response was 0.9 months, and to a major response was 1.9 months, though were longer in those with mutated CXCR4 at 1.7 months (p = 0.07) and 7.3 months (p = 0.01). Six patients had disease progression. The median progression-free survival (PFS) was not reached, and the 4-year PFS rate was 76%. There was also a non-significant lower 4-year PFS rate in patients with than without CXCR4 mutations (59% vs. 92%; p = 0.06). The most common treatment-related adverse events were fatigue, upper respiratory infection, and hematoma. Atrial fibrillation occurred in 20% of patients. Ibrutinib monotherapy induced durable responses in treatment-naive patients with WM. CXCR4 mutations impacted VGPR attainment, time to major response, and 4-year PFS rate.

PURPOSE BCL2 is overexpressed and confers prosurvival signaling in malignant lymphoplasmacytic cells in Waldenström macroglobulinemia (WM). Venetoclax is a potent BCL2 antagonist and triggers in vitro apoptosis of WM cells. The activity of venetoclax in WM remains to be clarified. PATIENTS AND METHODS We performed a multicenter, prospective phase II study of venetoclax in patients with previously treated WM ( NCT02677324 ). Venetoclax was dose-escalated from 200 mg to a maximum dose of 800 mg daily for up to 2 years. RESULTS Thirty-two patients were evaluable, including 16 previously exposed to Bruton tyrosine kinase inhibitors (BTKis). All patients were MYD88 L265P–mutated, and 17 carried CXCR4 mutations. The median time to minor and major responses was 1.9 and 5.1 months, respectively. Previous exposure to BTKis was associated with a longer time to response (4.5 v 1.4 months; P < .001). The overall, major, and very good partial response rates were 84%, 81%, and 19%, respectively. The major response rate was lower in those with refractory versus relapsed disease (50% v 95%; P = .007). The median follow-up time was 33 months, and the median progression-free survival was 30 months. CXCR4 mutations did not affect treatment response or progression-free survival. The only recurring grade ≥ 3 treatment-related adverse event was neutropenia (n = 14; 45%), including one episode of febrile neutropenia. Laboratory tumor lysis without clinical sequelae occurred in one patient. No deaths have occurred. CONCLUSION Venetoclax is safe and highly active in patients with previously treated WM, including those who previously received BTKis. CXCR4 mutation status did not affect treatment response.