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Revisiting the transcriptional analysis of primary tumors and associated nodal metastases with enhanced biological and statistical controls: application to thyroid cancer

ABSTRACT: The biology underlying nodal metastasis is poorly understood. Transcriptome profiling has helped to characterize both primary tumors seeding nodal metastasis and the metastasis themselves. The interpretation of these data, however, is not without ambiguities. Here we profiled the transcriptomes of 17 papillary thyroid cancer (PTC) nodal metastases, associated primary tumors and primary tumors from N0 patients. We also included patient-matched normal thyroid and lymph node samples as controls to address some limits of previous studies. We found that the transcriptomes of patient-matched primary tumors and metastases were more similar than of unrelated metastases/primary pairs, a result also reported in other organ systems, and that part of this similarity reflected patient background. We found that the comparison of patient-matched primary tumors and metastases was heavily confounded by the presence of lymphoid tissues in the metastasis samples. An original data adjustment procedure was developed to circumvent this problem. It revealed a differential expression of stroma-related gene expression signatures also regulated in other organ systems. The comparison of N0 vs. N+ primary tumors uncovered a signal irreproducible across independent PTC datasets. This signal was also detectable when comparing the normal thyroid tissues adjacent to N0 and N+ tumors, suggesting a cohort specific bias also likely to be present in previous studies with similar statistical power. Classification of N0 vs. N+ yielded an accuracy of 63%, but additional statistical controls not presented in previous studies, revealed that this is likely to occur by chance alone. To address this issue, we used large datasets from The Cancer Genome Atlas and showed that N0 vs. N+ classification rates could not be reached randomly for most cancers. Yet, it was significant, but of limited accuracy (<70%) for thyroid, breast and head and neck cancers.

ORGANISM(S): Homo sapiens

PROVIDER: GSE60542 | GEO | 2015/09/01

SECONDARY ACCESSION(S): PRJNA258507

REPOSITORIES: GEO

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Project description:The biology underlying nodal metastasis is poorly understood. Transcriptome profiling has helped to characterize both primary tumors seeding nodal metastasis and the metastasis themselves. The interpretation of these data, however, is not without ambiguities. Here we profiled the transcriptomes of 17 papillary thyroid cancer (PTC) nodal metastases, associated primary tumors and primary tumors from N0 patients. We also included patient-matched normal thyroid and lymph node samples as controls to address some limits of previous studies. We found that the transcriptomes of patient-matched primary tumors and metastases were more similar than of unrelated metastases/primary pairs, a result also reported in other organ systems, and that part of this similarity reflected patient background. We found that the comparison of patient-matched primary tumors and metastases was heavily confounded by the presence of lymphoid tissues in the metastasis samples. An original data adjustment procedure was developed to circumvent this problem. It revealed a differential expression of stroma-related gene expression signatures also regulated in other organ systems. The comparison of N0 vs. N+ primary tumors uncovered a signal irreproducible across independent PTC datasets. This signal was also detectable when comparing the normal thyroid tissues adjacent to N0 and N+ tumors, suggesting a cohort specific bias also likely to be present in previous studies with similar statistical power. Classification of N0 vs. N+ yielded an accuracy of 63%, but additional statistical controls not presented in previous studies, revealed that this is likely to occur by chance alone. To address this issue, we used large datasets from The Cancer Genome Atlas and showed that N0 vs. N+ classification rates could not be reached randomly for most cancers. Yet, it was significant, but of limited accuracy (<70%) for thyroid, breast and head and neck cancers. We profiled the transcriptomes of 11 primary PTCs with no detectable nodal invasion, 17 primary PTCs with nodal invasion and 17 patient-matched nodal metastases. We also profiled a number of control samples. These included 24 patient-matched normal thyroid tissues (11 from N0, 13 from N+ patients), and 4 normal lymph nodes; technical and biological replicates including additional nodal metastasis for 3 patients, adjacent blocks for 5 primary tumors, 4 normal thyroid tissues and 1 nodal metastasis.

Project description:Well-differentiated tumours (WDT) of the thyroid gland can be difficult to diagnose. Focal nuclear clearing can be suggestive of a papillary thyroid carcinoma (PTC), while questionable vascular or capsular penetration may raise the possibility of diagnosis of a follicular thyroid carcinoma (FTC). The recently proposed term “thyroid tumours of uncertain malignant potential” (TT-UMP) defines cases showing inconclusive morphological evidence of malignancy. We use microRNA (miRNA) expression profiling to analyze 42 well differentiated thyroid tumours including 7 follicular tumours of uncertain malignant potential (FT-UMP), 6 well differentiated tumours of uncertain malignant potential (WDT-UMP), 7 follicular thyroid adenomas (FTA), 5 follicular variant of papillary thyroid carcinoma (FV-PTC) 6 follicular thyroid carcinoma (FTC), and 11 conventional papillary thyroid carcinoma (C-PTC) with 6 C-PTC mutated for BRAFV600E (C-PTC-mut) and 5 not mutated: wild type (C-PTC-wt). Comparison of these 13 tumours of uncertain malignant potential (7 FT-UMP and 6 WDT-UMP) with those obtained from 16 PTC (11 C-PTC and 5 FV-PTC), 6 FTC and 7 FTA is performed in order to clarify the relationships between TT-UMP and the morphologically well characterized categories of thyroid tumours (i.e. C-PTC, FV-PTC, FTC and FTA). In first, each pathological sample (“L” for Lesional tissue) is compared with its matched control (“S” for Safe tissue) for the 42 patients (84 miRNA microarray slides). This control was taken from the same patient at a large distance from the tumour. Secondly, the perilesional tissue from the same patients but 2 (1 PTC and 1 adenoma, without enough RNA left) is compared to normal thyroid tissue (safe tissue reference) obtained from a patient who underwent total thyroidectomy for a laryngeal carcinoma that partially invaded the thyroid gland, to search for microRNA signatures of perilesional tissues (80 miRNA microarray slides).Experiments is performed with a miRNA microarray, referenced in GEO under the accession number GPL4717 (http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GPL4717). 42 Patients: 7 FT-UMP, 6 WDT-UMP, 7 FTA (+1 duplicate sample), 5 FV-PTC, 6 FTC (+ 2 duplicate samples), and 11 C-PTC. 44 dye-swap pairs and 1 with no dye swap pair for a total of 89 samples.

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Revisiting the transcriptional analysis of primary tumors and associated nodal metastases with enhanced biological and statistical controls: application to thyroid cancer

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