T-Cell Receptor Gamma Chain Gene Rearrangement by Homoduplex Analysis, Clinical Significance of Low Intensity Clonal Bands
JF Gradowski, MA Melan, SH Swerdlow, JA Kant. University of Pittsburgh Medical Center, Pittsburgh, PA
Background: Demonstration of T-cell clonality is a powerful tool used to support the often complicated diagnosis of T-lymphoid neoplasms. PCR approaches to clonality assessment most frequently target the T-cell receptor (TCR) gamma chain gene. Homoduplex analysis of PCR products is a sensitive approach to detect clonal fragments which avoids interpretative difficulties encountered when evaluating PCR products by size. We chose a 10% positive control as an initial cut-off to report results as positive. Samples with less intense homoduplex bands were reported as indeterminate; here we assess the clinical significance of those samples.
Design: Cases from a 15 month period were studied. Amplification was performed with TCR gamma chain V1-8, V9, V10 and V11 forward and Jg1 /Jg2 reverse primers. Products were analyzed on 20% PAGE gels following formamide treatment. 118 Samples with a visable homoduplex product <10% positive controls (Jurkat/ HSB-2 T-cell leukemia lines diluted in tonsil DNA) and no positive bands >10% with any other primers were identified. 47 displayed a distinct band <10% of the positive control while 71 displayed low intensity bands. All available hematopathology diagnoses and reports from subsequent biopsies were reviewed. 81 cases had a concurrent pathologic diagnosis with the majority of remaining cases peripheral blood specimens that were not further analyzed.
Results: 33 of 81 cases (40.7%) had demonstrable hematologic malignancy. These included 15 cases of T-cell lymphoma, 14 cases of B-cell lymphoma, 3 cases of precursor B-ALL, 1 Hodgkin lymphoma and 1 acute myeloid leukemia. The positive predictive value for a diagnosis of T-cell lymphoma was 18.5%. Of 34 cases with follow-up specimens but without a neoplastic diagnosis when TCR PCR testing was performed, 9 developed subsequent hematologic malignancy including 4 cases of mycosis fungoides, 2 cases of T-cell lymphoma, 2 cases of B-cell lymphoma and one plasma cell neoplasm.
Conclusions: TCR gamma gene rearrangement studies using PCR with visible homoduplex bands <10% positive controls are not infrequent. The low PPV for hematologic malignancy, and specifically T-cell malignancy, supports caution in the interpretation of such findings. At least some of these cases may represent oligoclonal proliferations.
Monday, March 9, 2009 9:30 AM
Poster Session I Stowell-Orbison/Autopsy Award # 181, Monday Morning