LOH analysis of free DNA in the plasma of patients with mucosal malignant melanoma in the head and neck.

Background: We have conducted charged-particle radiotherapy for mucosal malignant melanoma (MMM) in the head and neck, using carbon ion beams. However, even with the use of carbon ion radiotherapy that is characterized by high local tumor control, a significant number of patients develop metastases after therapy. We conducted research on the assumption that, in MMM, the detection of loss of heterozygosity (LOH) from free DNA in the circulating plasma may be of practical use in the diagnosis of recurrence and metastasis.

Methods: We took blood samples prior to therapy from 17 patients with MMM in the head and neck, and extracted free DNA in plasma. Four types of microsatellite markers were used for LOH detection.

Results: LOH was detected in 1 of 5 patients (20%) for D1S243, 2 of 5 patients (40%) for D6S311, 11 of 17 patients (65%) for D9S161, and 1 of 6 patients (17%) for D19S246.

Conclusion: Evidence based on the irradiated tumor volume suggested a tendency for the group of patients found to have LOH in two loci to have a larger mean tumor volume than the patient groups with no detectable LOH or with LOH detectable in only one locus. Of the 17 patients in this study 4 patients had recurrence and/or metastasis, and all 4 of these patients were found to have LOH in at least one or more loci for any region. LOH analysis of free DNA in plasma may be useful for the early diagnosis of MMM.