Impact of Baseline Osseous Involvement on Outcomes in Patients with Lymphoplasmacytic Lymphoma (LPL)/Waldenstrom’s Macroglobulinemia (WM)

Background: Lymphoplasmacytic lymphoma (LPL) is an indolent B-cell non-Hodgkin lymphoma that can involve the bone marrow and cause a monoclonal IgM proteinemia, in which case it is considered Waldenstrom’s macroglobulinemia (WM). Involvement of osseous structures in patients (pts) with LPL/WM is uncommon with osteopenia/porosis being the most frequent finding (Vermess, Radiology 1972). The prognostic significance of osseous involvement in LPL/WM is unknown.

Methods: To assess the impact of baseline osseous involvement on outcomes in pts with LPL/WM, we performed a single-center retrospective cohort study of pts with LPL/WM. Osseous involvement was defined as the presence of lytic or sclerotic lesions, pathologic fractures, FDG-avid lesions in osseous structures on positron emission tomography (PET) scans, or osteopenia/porosis that were not explained by alternate etiologies at the time of LPL/WM diagnosis.

Baseline clinical characteristics and outcomes were assessed, including overall response rate (ORR), defined as rate of minor response (MR) + partial response (PR) + very good partial response (VGPR) + complete response (CR), major response rate (MRR), defined as PR+VGPR+CR, diagnosis to treatment interval (DTI), progression-free survival (PFS), and overall survival (OS). PFS was defined from initiation of first line treatment to progression or death, and OS from time of diagnosis to death from any cause with censoring of those alive at last follow-up.

Baseline variables are reported descriptively with median and range for continuous variables and frequency and percentage for categorical variables. Kaplan-Meier method was used to describe survival outcomes and log-rank test was used to compare groups. Cox proportional hazard regression models were used to estimate the hazard ratios (HR) for risk of progression or death. A multivariable analysis (MVA) was built to evaluate independent risk factors for outcomes incorporating significant factors from univariable analysis (UVA) as well as clinically important factors such as level of IgM proteinemia.

Results: A total of 77 pts were identified, 20 (26%) with baseline osseous involvement and 57 (74%) without. Six pts (30%) had lytic lesions, 5 FDG-avid PET lesions (25%), 4 pathologic fractures (20%) and sclerotic lesions (20%) each, and 1 osteopenia/porosis (5%). Pts with osseous involvement tended to be older at diagnosis (70 years vs 63 years, p=0.014) and at treatment initiation (73 years vs 64 years, p=0.003) and were exclusively white (100% vs 83%, p=0.05) compared to pts without osseous involvement. The rest of the baseline characteristics were balanced between the two groups, including gender, Eastern Cooperative Oncology Group (ECOG) performance status, presence of B symptoms, IgM levels, non-osseous extranodal involvement, MYD88/CXCR4 mutations, elevated lactate dehydrogenase (LDH) level, and presence of complex karyotype. The median follow up was 5.6 years.

In total, 73 (95%) pts received disease-directed treatment (17 with osseous involvement vs 56 without) with a median DTI of 0.11 years (95% CI: 0.05, 0.62) and 0.12 years (95% CI: 0.08, 0.39) among pts with and without osseous involvement. Treatment types were balanced across groups with 26% receiving anti-CD20 monoclonal antibody monotherapy, 63% receiving chemoimmunotherapy, and 11% receiving other therapies such as Bruton tyrosine kinase inhibitors or proteasome inhibitors. Among treated pts, the ORR (80% vs 91%, p=0.35) and MRR (80% vs 84%, p=0.71) were comparable between those with and without osseous involvement. PFS was similar between pts with (median 7.79 years [95% CI: 3.82, not reached (NR)]) and without osseous involvement (median 6.33 years [95% CI: 4.28, NR] p=0.38). In the entire cohort, pts with osseous involvement had comparable OS compared to pts without osseous involvement (median NR [95% CI: 6.42, NR] vs 13.1 years [95% CI: 8.85, NR], p=0.98). UVA and MVA Cox model showed increasing age was significantly associated with inferior OS (HR 1.08 [95% CI: 1.02, 1.15] p=0.005).

Discussion: To our knowledge, this is the first study to look at the prognostic significance of osseous involvement at diagnosis in pts with LPL/WM. We found that the presence of osseous involvement at baseline did not affect response rates, DTI, or survival. Larger studies are needed to validate our findings and further clarify the significance of osseous involvement in LPL/WM.