Weekly x 4 induction therapy with the anti-CD20 antibody rituximab: effect on circulating t(14;18)(+) follicular lymphoma cells

Radiotherapy with rituximab may be better than radiotherapy alone in first-line treatment of early-stage follicular lymphoma: is it time to change the standard strategy?

Early-stage follicular lymphoma (FL) has traditionally been treated with involved-field radiotherapy (RT). Rituximab (R) is a low-toxic, efficient systemic therapy for FL, but there are no data about its clinical impact in early FL. We retrospectively analyzed 93 patients with stage I-II indolent FL treated with RT (n=65) or RT+R (n=14) or R alone (n=14). Median follow-up was 5.0 years for patients with RT, 2.8 years for the RT+R subgroup and 2.5 years for patients treated with R. The complete response rate was 92%, 100% and 86% (not significant) and the median PFS was 3.3 years, not reached and 4.9 years (p=0.035) for the RT, RT+R and R arms, with no impact on overall survival. R combined with RT seems to give better results in terms of global FL control, but longer follow-up and prospective comparison are needed to verify these results.

The persistence of t(14;18)-bearing cells in lymph nodes of patients with follicular lymphoma in complete remission: the evidence for 'a lymphoma stem cell'

Monitoring of t(14;18) in blood or bone marrow in follicular lymphoma (FL) remains controversial. We attempted to monitor t(14;18) in lymph nodes by ultrasound-guided fine needle aspirations (UG-FNA). First, we confirmed t(14;18) in 27/31 UG-FNAs of lymph nodes with fluorescent in situ hybridisation (FISH) and/or polymerase chain reaction (PCR) in patients with advanced disease. In complete (CR) and molecular remission, there were repeated 18 UG-FNAs in 17 patients. Five of 18 UG-FNA were technically unsuccessful and 6/18 samples contained fibrosis. Despite that, these patients had a better prognosis. In 7/7 aspirations in six patients, t(14;18) was detected. Three patients are still in CR, even one of them remains in long lasting remission despite two consecutive evidences of t(14;18) in UG-FNA. Another three of these patients relapsed a few months after UG-FNA. This study is proof of the principle of the detection of residual t(14;18) bearing cells in previously involved lymph nodes despite patients being in remission.

Rituximab (monoclonal anti-CD20 antibody): mechanisms of action and resistance

Rituximab, a chimeric monoclonal antibody targeted against the pan-B-cell marker CD20, was the first monoclonal antibody to be approved for therapeutic use. Treatment with rituximab at standard weekly dosing is effective in more than 50% of patients with relapsed or refractory CD20-positive follicular non-Hodgkin's lymphoma, but is not curative. It is less effective in other subtypes of CD20-positive lymphoma and for retreatment, even with CD20 still expressed. Thus, binding of rituximab to CD20 is not sufficient to kill many lymphoma cells, indicating that there are mechanisms of resistance. Mechanisms of cell destruction that have been demonstrated to be activated by rituximab binding to CD20 include direct signaling of apoptosis, complement activation and cell-mediated cytotoxicity. The relative importance of each of these mechanisms in determining clinical response to rituximab treatment remains a matter of conjecture. Thus, the role of various resistance pathways, some documented in experimental systems and others still hypothetical, remains uncertain. Resistance could potentially be mediated by alterations in CD20 expression or signaling, elevated apoptotic threshold, modulation of complement activity or diminished cellular cytotoxicity. As the first of an expanding class of anticancer agents, lessons learned regarding the mechanism of rituximab action and resistance will be of increasing importance.