Background DNA tumor markers in plasma and serum such as point mutations, hypermethylation of tumor suppressor genes, and viral sequences have attracted much interest. We investigated clonal Ig DNA rearrangements in the plasma of AIDS-related lymphoma (ARL) patients (pts).
Methods We evaluated specimens for Ig rearrangements from pts with ARL using fluorescently-labeled multiplex primers targeting IgH and IgK. PCR products were analyzed by capillary electrophoresis. Re-amplified PCR products from plasma and tumor were cloned and sequenced.
Results Clonal IgH DNA spikes were seen in plasma at baseline in 5 of 10 pts. Clonal DNA was detected in plasma in pts with either early or advanced stage disease, with or without marrow involvement. Presence of a plasma clone was associated with high LDH. Serial specimens were available from 4 pts. In 2 pts who died with primary refractory disease, clonal peaks remained present after the administration of chemotherapy. In a pt with disease that initially responded and then relapsed, clonal DNA disappeared with chemotherapy, then reappeared presaging relapse and death. In 4 pts, matching serum specimens were available. Results were similar in both types of specimens with identical sized rearrangements amplified from matched specimens. Furthermore in 2 pts, the IgH amplification products from plasma and tumor were sequenced and confirmed to be identical. Two pts with positive IgH amplification products were also screened for light chains in the plasma and in both, clonal IgK rearrangements were detected. For purposes of comparison, plasma from healthy donors (n=20) and AIDS pts with Kaposi’s sarcoma (KS) (n=10) were also surveyed. Clonal Ig DNA rearrangements were not detected in any of these.
Conclusions These results are consistent with observations suggesting that free tumor DNA can often be detected in plasma or serum of cancer pts. The absence of clonal Ig DNA in plasma from healthy donors and pts with AIDS KS suggests that detection of such DNA may be highly specific. Identification of the same Ig rearrangement and sequence in plasma and tumor is consistent with this interpretation. Serial monitoring of circulating clonal DNA appears to track—and perhaps anticipate—clinical evidence of disease. These approaches may be especially valuable in ARL where FDG uptake reflective of inflammatory disease or benign lymphoproliferation detected by PET scan often renders interpretation of imaging ambiguous. Similarly, elevated LDH in this population is relatively non-specific.
Disclosure: No relevant conflicts of interest to declare.