We assessed the reproducibility and clonality of these eight differentially methylated regions in our cohort of cases with multiple spatially separate tumour samples, matched benign tissue and blood DNA samples (Fig. 1b and Supplementary Figure 1f, g, h, i, j, k, l, m).
A separate study of a large number of thyroidectomies for Hürthle cell tumours found that about 20% of cases showed multiple separate Hürthle cell tumours, and that these were significantly younger and much more often female than the solitary tumours (Katoh et al, 1998).
In our cohort of multiple spatially separated tumour samples, we found that HES5 expression was decreased in tumour cores compared with matched benign tissue and that HES6 was also increased in some of those tumour cores, consistent with HES5 silencing in tumourigenesis and additional mechanisms regulating HES6 expression (Supplementary Figure 5e and f).
Tissues were microdissected to separate tumour from normal tissues.
The fundamental problem is to identify and separate tumour initiating cells from more differentiated tumour cells.
Therefore using our cohort of cases with multiple tumour foci and matched benign samples, we found that hypermethylation at the HES5 promoter region was observed across tumour samples from all patients and in all spatially separated tumour foci from the same patient.
Moreover, for patients with multiple tumours, an approximate tumour location was given by a range of slices where the tumour could be located.
Campbell BA, Horsman DE, Maguire J, Young S, Curman D, Ma R, Thiessen B. Chromosomal alterations in oligodendroglial tumours over multiple surgeries: is tumour progression associated with change in 1p/19q status?
For patients with multiple, apparently separate, primary lung adenocarcinomas, each tumour should be evaluated.
To address ITH in this study, lysates were taken for multiple, spatially separate areas of each primary tumour.
