Establishment of aspiration biopsy nucleic acid diagnosis of malignant lymphoma

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Distinguishing between thyroid malignant lymphoma and lymphocytic thyroiditis (Hashimoto's thyroiditis) is quite difficult and problematic. B-cell lymphomas display clonal immunoglobulin heavy chain (IgH) gene rearrangement, and Southern blot hybridization (SBH) is often used for detection of the monoclonality of the IgH gene. However, SBH is often problematic, since it requires a large volume of samples. Vectorette PCR is a method for amplifying DNA fragments of which the 5' sequences are unknown, using a modified linker to facilitate specific amplification of the targeted sequence, and it requires only 200 ng of genomic DNA to start with, which is easily obtainable by fine needle aspiration biopsy. We examined the efficiency in detecting the monoclonality of IgH gene in thyroid malignant lymphomas by vectorette PCR, which we started with 200 ng of genomic DNA obtained either from tissue samples or tumor aspirates. In the analysis using tissue samples, monoclonality was detected in 36 (76.6%) of 47 malignant lymphomas, whereas it was not detected in 10 samples of tissue of Hashimoto's thyroiditis. The sensitivity was almost the same as that with SBH in which monoclonality was detected in 33 (73.3%) of 45 malignant lymphomas. Further, one case in which aspirated tumor cells showed monoclonality in the IgH gene by vectorette PCR revealed to be diffuse large cell B-cell lymphoma by histopathological diagnosed after open biopsy. These results suggest that vectorette PCR may be a substitute for SBH, and since it requires only a small volume of samples, it is also used in the analysis of aspiration biopsies.