G17V Rhoa Mutation in Circulating DNA Is a Useful Marker for Diagnosis of AITL and AITL-Related Lymphoma

[Background] Angioimmunoblastic T-cell lymphoma (AITL) is a subtype of peripheral T-cell lymphoma. We and others reported that the G17V RHOA mutation is frequent and highly specific to AITL and AITL-like peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS). Thus, detection of this mutation serves as a novel diagnostic strategy for AITL and AITL-like PTCL-NOS.

[Aim] Analysis of disease-specific mutations in serum DNA from AITL and PTCL-NOS patients.

[Method] Genomic DNA was collected from tumors and sera from 16 AITL and PTCL-NOS patients and 11 B-cell malignancy patients. Seven out of 16 T-cell lymphoma and all B-cell malignancy patients did not receive prior treatment. Amplicon-based sequencing by Ion Torrent PGM was performed to analyze the G17V RHOA mutation as well as TET2 and DNMT3A mutations in these samples.

[Result] Three out of 7 tumor samples of T-cell lymphoma patients whose serum was preserved prior to treatment were positive for the G17V RHOA mutation. In the serum of these 3 patients, allele frequencies of the G17V RHOA mutation were 0.006 - 0.072 (mean 0.015, SDV 0.026), while 0 (mean 0, SDV 0) in the serum of the remaining 4 T-cell lymphoma patients and all the 11 B-cell malignancy patients whose tumor samples did not show RHOA mutation. Because we set cut off value as 0.002 (0.2%) based on the ROC curve, RHOA mutation was segregated into positive and negative faithfully according to whether the mutation was identified in the tumor samples. Then, we analyzed TET2 and DNMT3A mutations in sera of 5 patients whose tumor samples were positive for TET2 (n=2; a single mutation in each sample) and DNMT3A (n=3; 5 mutations all together), respectively. TET2 and DNMT3A mutations were detected in all the 5 sera, although 2 out of the 5 DNMT3A mutations were undetectable. In the clinical courses, RHOA mutations became undetectable after the treatment in sera of all the 3 patients whose pre-treatment sera were positive, while TET2 mutations were detected even after the treatment in sera of both patients whose pre-treatment sera were positive.

[Conclusion] Biopsy is sometimes difficult in lymphoma patients with progressed diseases. Identification of the disease-specific G17V RHOA mutation in serum may provide a non-invasive method to diagnose AITL and AITL-like PTCL-NOS, although inapplicable to detect minimum residual disease. Stable detection of TET2 mutations regardless of chemotherapy might indicate the presence of the mutations in the 'pre-cancerous cells' which are resistant to the chemotherapy.