Detailed assessment of chromosome 22 aberrations in sporadic pheochromocytoma using array‐CGH

Abstract

Pheochromocytoma is a predominantly sporadic neuroendocrine tumor derived from the adrenal medulla. Previous low resolution LOH and metaphase-CGH studies reported the loss of chromosomes 1p, 3q, 17p and 22q at various frequencies. However, the molecular mechanism(s) behind development of sporadic pheochromocytoma remains largely unknown. We have applied highresolution tiling-path microarray-CGH with the primary aim to characterize copy number imbalances affecting chromosome 22 in 66 sporadic pheochromocytomas. We detected copy number alterations on 22q at a frequency of 44%. The predominant finding was monosomy 22 (30%), followed by terminal deletions in 8 samples (12%) and a single interstitial deletion. We further applied a chromosome 1 tiling-path array in 7 tumors with terminal deletions of 22q and found deletions of 1p in all cases. Our overall results suggest that at least 2 distinct regions on both 22q and 1p are important in the tumorigenesis of sporadic pheochromocytoma. A large proportion of pheochromocytomas also displayed indications of cellular heterogeneity. Our study is to our knowledge the first array-CGH study of sporadic pheochromocytoma. Future analysis of this tumor type should preferably be performed in the context of the entire human genome using genome-wide array-CGH, which is a superior methodological approach. Supplemental material for this article can be found on the International Journal of Cancer website at http://www.interscience.wiley. com/jpages/0020-7136/suppmat/index.html. ' 2005 Wiley-Liss, Inc.Key words: genomic microarray; chromosome 1; PTCH2; deletions; amplifications; tiling-path array; tumor heterogeneity Pheochromocytoma is a neuroendocrine tumor, derived from chromaffin cells in the adrenal medulla. The tumors usually secrete catecholamines and are benign in more than 90% of cases.It is difficult to distinguish clinically and histopathologically between benign and malignant pheochromocytoma. The only certain proof of malignancy is the occurrence of distant metastases, which develop in lung, liver and lymph nodes. Pheochromocytomas occur as a feature of several inherited cancer syndromes, such as multiple endocrine neoplasia type 2 (MEN2; MIM 171400), von Hippel-Lindau syndrome (VHL; MIM 193300) and to a lesser extent in neurofibromatosis type 1 (NF1; MIM; 162200). 1 MEN2 is caused by germline mutations in the RET proto-oncogene located on 10q11.2, whereas VHL results from germline mutations in the VHL tumor suppressor gene situated on 3p25-p26. Pheochromocytoma also occurs as isolated familial tumours, which have been associated with germline mutations in RET, VHL, SDHB (succinate dehydrogenase complex, subunit B) and SDHD (succinate dehydrogenase complex, subunit D) in up to 25% of cases.2 However, the vast majority of pheochromocytoma (75%) is considered to be sporadic, and the molecular mechanism(s) underlying the development of these tumors is largely unknown. Somatic mutations in RET, VHL, NF1 and SDHD have only been found in a minority of sporadic pheochromocytomas...

Intra-tumoral molecular heterogeneity in benign and malignant pheochromocytomas and extra-adrenal sympathetic paragangliomas

“…Jarbo et al (2005) reported that the ratios of chromosome 22q loss in some PCC samples were higher than expected for a single allele ratio, and suggested this could be due to intra-tumoral heterogeneity. Diaz-Cano et al (2000) investigated heterogeneity of sporadic and MEN 2-related PCC and adrenal medullary hyperplasia (AMH) nodules, by determining the methylation patterns of the androgen receptor (AR) gene, localized on the X-chromosome.…”

“…While loss of chromosome 1p is the most common genetic aberration reported in sporadic PCC (Dannenberg et al 2000, Edstrom et al 2000, Cascon et al 2005), particular genetic alterations have been demonstrated in syndrome-related PCC (Edstrom et al 2000, Lui et al 2002, Jarbo et al 2005. Generally, MEN 2-related PCCs show loss of chromosomes 1p and 3q (Edstrom et al 2000, Jarbo et al 2005, SDHD-related PCCs and PGLs display loss of chromosome 11 (Hensen et al 2004), and in NF1-related tumors, frequent loss of 1p and 17q is found (Edstrom et al 2000, Bausch et al 2007.…”

“…Generally, MEN 2-related PCCs show loss of chromosomes 1p and 3q (Edstrom et al 2000, Jarbo et al 2005, SDHD-related PCCs and PGLs display loss of chromosome 11 (Hensen et al 2004), and in NF1-related tumors, frequent loss of 1p and 17q is found (Edstrom et al 2000, Bausch et al 2007.…”

Array-comparative genomic hybridization in sporadic benign pheochromocytomas

“…This technique has facilitated the analysis of chromosomes 21 and 22 that were difficult to analyze in conventional CGH. Recently, copy number imbalances affecting chromosome 22 were confirmed by submegabase array-CGH in 44% (29/66) of PCC analyzed, a percentage that had not been described in conventional CGH (Jarbo et al 2006). In addition, the tiling order of bacterial artificial chromosome (BAC) clones also has the advantage to rule out mismapped clones, and gives precise breakpoint information.…”

Frequent loss of 17p, but no p53 mutations or protein overexpression in benign and malignant pheochromocytomas

“…Loss of heterozygosity (LOH) and comparative genomic hybridization (CGH) studies performed by us and others have reported allelic losses at 1p, 3pq, 17p, and 22q, but corresponding genes have not been identified. [3][4][5][6] Particularly 17p, the chromosome arm where the p53 gene is located, is interesting to investigate knowing that aberrations in this gene are implicated in many inherited and sporadic forms of malignancy, such as colon, lung, brain, and breast tumors. 7 p53 is functionally involved in guarding the stability of the genome.…”