Multifocal papillary carcinomas usually
arise from one clone of thyroid cells
(July 2006)
The background of the study. Patients with papillary
carcinoma of the thyroid may have small foci of carcinoma in their
thyroid gland addition to their main tumor, which may represent
spread of the main tumor or independent tumors. In this study, the
relationships between tumors in the same patient were studied using
analysis of three genes and X-chromosome inactivation.
How the study was done. Papillary-carcinoma tissue
from 23 women was analyzed. The largest tumor in each woman ranged
from 0.3 to 4.5 cm in diameter, and they had from one to five smaller
noncontiguous tumors (total, 64) confined to the thyroid gland.
Tumor and normal thyroid tissue were identified on microscope slides,
DNA was extracted from the tissue, and a polymorphic gene on each
of three different chromosomes was amplified. The pattern of X-chromosome
inactivation was determined by amplification of its constituent
androgen-receptor gene and detection of active and inactive forms
of this gene.
The results of the study. The genetic composition
of all the tumors was similar, indicating common parentage, in 20
of the 23 women (87 percent). They included 1 woman with 5 tumors,
1 with 4 tumors, and 7 with 3 tumors. In the 1 woman with 6 tumors,
the results were similar in 5.
The pattern of X-chromosome inactivation was similar in all the
tumors in 19 of the 20 women (95 percent). In 6 women, all the tumors
had both an active and an inactive X chromosome; in 13, all the
tumors had only an active or only an inactive X chromosome.
The conclusions of the study. In many patients
with multifocal papillary thyroid carcinoma, the genetic composition
of each tumor is the same, suggesting common parentage and therefore
that tumors can spread within the thyroid.
The original article. McCarthy RP, Wang M, Jones
TD, Strate RW, Cheng L. Molecular evidence for the same clonal origin
of multifocal papillary thyroid carcinomas. Clin Cancer Res 2006;12:2414-8.
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