The Lancet's Online First section has released a new set of data from the major Primary Rituximab and Maintenance Study (PRIMA), a massive analysis of over 1200 patients in 25 countries. Rituximab maintenance is a common strategy for converting some partial responses to complete remission, and in others delaying disease progression, following initial treatment. It usually lasts two years and involves about 6-12 additional cycles of therapy. Cancer Care Ontario, for instance, funds eight maintenance doses over two years, or one every three months.
Once again, the PRIMA data show impressive progression-free survival statistics for follicular lymphoma patients -- meaning patients who, following treatment have both survived and experienced no further disease growth. 1217 patients were enrolled on the PRIMA study; after initial therapy with one of several rituximab-based regimens (R-CHOP, R-CVP, or R-FCM, which contains fludarabine), 1019 people with a detectable response were randomized to either untreated observation or to 2 years of rituximab maintenance.
The short-term benefits of rituximab maintenance are now very apparent. After the 2-year maintenance cycle was complete, 72% of patients were still in complete remission, compared with just over 50% in the untreated arm. Three years out, 75% of maintenance patients still had not experienced disease progression, compared with just 58% in the untreated group. This confirms other studies which suggest that rituximab maintenance cuts the relapse rate roughly in half over the short term.
What PRIMA can't yet answer is the increasingly urgent question of whether rituximab maintenance actually affects overall survival. Overall (long-term) survival statistics are a serious problem in indolent lymphoma research, because the natural history of the disease is already long enough that it can't easily be evaluated in a single trial. So far, the PRIMA data suggests no significant impact on overall survival. However, this may reflect the fact that 2- and 3-year survival statistics for follicular lymphoma are already so high that it is difficult to detect improvement. If benefits do exist, it may take a number of years for them to become apparent in the data.
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