Circulating nucleic acids have been explored as tumor markers in several malignancies. Lymphoma offers a special opportunity to develop tumor DNA markers. Normal B cells undergo Ig rearrangements to generate antibody diversity. In B cell malignancies, the Ig gene rearrangements are monoclonal. Molecular diagnostic tests are widely employed in tumor specimens to detect these clone-specific Ig rearrangements when histology and immunohistochemistry are ambiguous. While long-lived plasma cells can secrete Ig over years, a B cell can only release its unique clone once. In order to sustain the presence of Ig DNA, ongoing cellular proliferation and death is required, suggesting that detection in the plasma may be a specific marker for presence of lymphoma. We previously reported our experience in screening plasma from patients (pts) with AIDS-related lymphomas (Blood 110(11):1579, 2007). The feasibility of this approach and promising results led to a pilot study evaluating clonal Ig DNA in pts with newly diagnosed diffuse large B cell lymphoma (DLBCL) without HIV.
Plasma is screened for clonal Ig DNA using standardized fluorescently-labeled multiplex primers (InVivoScribe) targeting IgH rearrangements. Rearranged Ig DNA is amplified by polymerase chain reaction (PCR), and the amplified products are separated by size using capillary electrophoresis. International prognostic index (IPI) scores and results of baseline PET/CT scans, including standardized uptake value (SUV)max scores are collected from pts to determine the impact of these findings on the ability to detect clonal Ig DNA.
Of 36 plasma specimens evaluated to date, 28 (78%) had clonal IgH rearrangements. Clonal and polyclonal controls yielded appropriate results. Tumor specimens are available from 22 patients, including 19 formalin-fixed paraffin-embedded (FFPE) and 5 fresh frozen tissue (FFT) specimens (2 pts have both FFPE and FFT). Eight FFPE tumor specimens have been evaluated; monoclonal IgH rearrangements were present in 5 (63%), 2 had polyclonal rearrangements, and 1 had no detectable IgH rearrangements. The median IPI scores were 1.5 (75% of pts had scores of 0–2) for the group without detectable plasma clonal Ig DNA and 2 (67% of pts had scores of 0–2) for the group with detectable plasma clonal Ig DNA. Wilcoxon 2-sample test demonstrated no difference between the 2 groups with respect to IPI scores (p= 0.50). Pre-treatment PET/CT scans were interpreted as positive in 30 of 33 pts. Two pts with negative PET/CT and corresponding IPI scores of 0 and 1 respectively, did not have detectable plasma clonal Ig DNA. One pt with a negative PET/CT had an IPI score of 0 and had detectable clonal Ig DNA in the plasma. In a T-test comparison, there was no evidence for a difference in SUVmax among pts with and without detectable clonal Ig DNA (p = 0.31).
Circulating clonal Ig DNA is detectable in pts with newly diagnosed DLBCL even with low IPI scores and negative PET/CT scans. Relatively small pt numbers limit the interpretation of the IPI/FDG-PET findings with respect to the detection of clonal Ig DNA in the plasma, and larger studies are needed to better appreciate if there is any correlation. Studies are ongoing to determine whether clonal Ig plasma DNA persists after the initiation of therapy, and whether the presence of clonal Ig DNA in plasma might complement information obtained from early interim FDG-PET in identifying patients likely to fail conventional therapy. Continued analysis of paired tumor/plasma specimens will clarify if plasma clonal Ig DNA is tumor derived.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.