There are at least two potential explanations for this behavior: 1) anti-CD-20 and combination therapy are most effective at early times, when both as-bcl-2 and anti-CD-20 are in maximum abundance, or 2) the therapy is more effective with the most vulnerable of a heterogeneous population of tumor cells, which are eliminated in the first week, leaving the less vulnerable cells to dominate tumor growth after 7 days. Here, BCL2 is linked to neoplasm.