Simple numerical chromosome aberrations in two pituitary adenomas

Insights into pituitary tumorigenesis: from Sanger sequencing to next-generation sequencing and beyond

Introduction: This review explores insights provided by next-generation sequencing (NGS) of pituitary tumors and the clinical implications.Areas covered: Although syndromic forms account for just 5% of pituitary tumours, past Sanger sequencing studies pragmatically focused on them. These studies identified mutations in MEN1, CDKN1B, PRKAR1A, GNAS and SDHx causing Multiple Endocrine Neoplasia-1 (MEN1), MEN4, Carney Complex-1, McCune Albright Syndrome and 3P association syndromes, respectively. Furthermore, linkage analysis of single-nucleotide polymorphisms identified AIP mutations in 20% with familial isolated pituitary adenomas (FIPA). NGS has enabled further investigation of sporadic tumours. Thus, mutations of USP8 and CABLES1 were identified in corticotrophinomas, BRAF in papillary craniopharyngiomas and CTNNB1 in adamantinomatous craniopharyngiomas. NGS also revealed that pituitary tumours occur in the DICER1 syndrome, due to DICER1 mutations, and CDH23 mutations occur in FIPA. These discoveries revealed novel therapeutic targets and studies are underway of BRAF inhibitors for papillary craniopharyngiomas, and EGFR and USP8 inhibitors for corticotrophinomas.Expert opinion: It has become apparent that single-nucleotide variants and small insertion/deletion DNA mutations cannot explain all pituitary tumorigenesis. Integrated and improved analyses including whole-genome sequencing, copy number, and structural variation analyses, RNA sequencing and epigenomic analyses, with improved genomic technologies, are likely to further define the genomic landscape.

Molecular cytogenetic analysis in the study of brain tumors: findings and applications

Classic cytogenetics has evolved from black and white to technicolor images of chromosomes as a result of advances in fluorescence in situ hybridization (FISH) techniques, and is now called molecular cytogenetics. Improvements in the quality and diversity of probes suitable for FISH, coupled with advances in computerized image analysis, now permit the genome or tissue of interest to be analyzed in detail on a glass slide. It is evident that the growing list of options for cytogenetic analysis has improved the understanding of chromosomal changes in disease initiation, progression, and response to treatment. The contributions of classic and molecular cytogenetics to the study of brain tumors have provided scientists and clinicians alike with new avenues for investigation. In this review the authors summarize the contributions of molecular cytogenetics to the study of brain tumors, encompassing the findings of classic cytogenetics, interphase- and metaphase-based FISH studies, spectral karyotyping, and metaphase- and array-based comparative genomic hybridization. In addition, this review also details the role of molecular cytogenetic techniques in other aspects of understanding the pathogenesis of brain tumors, including xenograft, cancer stem cell, and telomere length studies.

Molecular defects in the pathogenesis of pituitary tumours

The majority of pituitary adenomas are trophically stable and change relatively little in size over many years. A comparatively small proportion behave more aggressively and come to clinical attention through inappropriate hormone secretion or adverse effects on surrounding structures. True malignant behaviour with metastatic spread is very atypical. Pituitary adenomas that come to surgery are predominantly monoclonal in origin and roughly half are aneuploid, indicating either ongoing genetic instability or transition through a period of genetic instability at some time during their development. Few are associated with the classical mechanisms of tumour formation but it is generally believed that the majority harbour quantitative if not qualitative differences in molecular composition compared to the normal pituitary. Despite their prevalence and the ready availability of biopsy material, at the present time, the precise molecular pathogenesis of the majority of pituitary adenomas remains unclear. This review summarizes current thinking.

Genesis of pituitary adenomas: state of the art

In recent years, remarkable progress has been made in the understanding of the pathogenesis of pituitary tumors. Pituitary tumors originate from the uncontrolled proliferation of a single transformed cell in which an initiating event has caused a gain of proliferative function. After the initiation, promoting factors cooperate in the clonal expansion. Common oncogenes, such as ras, are only exceptionally involved. The only activating mutations identified so far are gsp mutations causing the constitutive activation of cAMP pathway. However, gsp-positive adenomas are not associated to a more aggressive tumoral phenotype. The oncogenic potential of gsp mutations is limited by a more rapid degradation of the mutant Gs(alpha) with respect to the wild-type protein, and by a faster removal of cAMP due to increased phosphodiesterase activity. Estrogen-inducible gene sequences with transforming properties (pituitary tumor-transforming gene (PTTG)) have been identified in human pituitary tumors. Human pituitary tumor-transforming gene (hPTTG) is involved both in early pituitary tumorigenesis, as it causes in vitro and in vivo transformation acting as a transcription activator, and in tumor progression, as it regulates the production of basic fibroblast growth factor (bFGF), a potent activator of angiogenesis and mitogenesis. Moreover, a role of cyclin D1 in pituitary tumorigenesis is emerging. The allelic loss of loci for unknown oncosuppressor genes are currently under investigation, while an exceedingly limited role for menin gene and RB1 has been demonstrated for sporadic pituitary tumors. Abnormal methylation that predisposing toward genetic instability may favor the allelic loss or the reduced expression of oncosuppressor genes, is also an emerging field of investigation. Several promoting factors, including the excessive action of physiological stimulators, the defective action of inhibitors, the susceptibility to respond to inappropriate stimuli and the locally produced growth factors, help in tumor progression. The study of homeobox genes that intervene in pituitary cell differentiation may help in expanding our knowledge in pituitary tumor cell genealogy.

Chromosomal aberrations in sporadic pituitary tumors

Pituitary adenomas are common intracranial neoplasms that may be hormone-secreting or nonfunctional. Genetic defects associated with some pituitary tumors have been identified, although our understanding of the underlying molecular mechanisms remains incomplete. We have studied 75 sporadic pituitary tumors, representing the major clinical subtypes, by comparative genomic hybridization (CGH) with the aim of assessing for DNA copy number changes. CGH revealed chromosomal imbalances in 34 adenomas (45.3%), whereby gains were 4.9 times more frequently observed than losses. Most of the genetic alterations detected by CGH affected entire chromosomes (108/131, 82.4%). Gain of genetic material was observed predominantly on chromosomes X (24/75, 32%), 19 (12/75, 16%), 12 (6/75, 6.7%), 7 and 9 (5/75, 6.7%), whereas loss of DNA sequences most frequently affected chromosomes 11 (4/75, 5.3%), 13 and 10 (3/75, 4%). There were no significant differences in the CGH results for the individual clinical subtypes of pituitary tumors. These results reveal a nonrandom pattern of chromosomal alterations in pituitary tumors, in particular gains of entire chromosomes, and this may contribute to the development of such neoplasms.

Genetic heterogeneity and alterations in chromosome 9 loci in a localized region of a functional pituitary adenoma

The molecular alterations reported in pituitary adenomas include mutations at the G(s)alpha in somatotrophinomas, and hypermethylation of the p16 tumor suppressor gene. There are, however, no reports of genomic instability or intratumor genetic heterogeneity in pituitary adenomas. We have studied the microsatellite loci on the short arm of chromosome 9 (9p) and the DNA fingerprinting pattern, of adjacent compartments, about 2 mm across, in a functional chromophobe pituitary adenoma secreting growth hormone and prolactin. The microsatellite loci were studied by PCR amplification using locus specific primers, while the DNA fingerprinting pattern was studied by randomly amplified polymorphic DNA (RAPD) analysis. Normal leukocyte DNA was taken as control. Only one compartment (Ta) showed alterations in several of the microsatellite loci and in the RAPD pattern vis a vis corresponding normal DNA and also the other two compartments of the tumor. This provides evidence for the localized nature of genomic instability in this tumor.

Chromosomal abnormalities in pituitary adenomas

Cytogenetic studies were conducted on 30 pituitary adenomas, using both direct and/or short-term in vitro culture methods. An apparently normal chromosome complement was found in 14 tumors; 5 adenomas were characterized by hyperdiploid or near-triploid modal chromosome numbers. Recurrent numerical deviations were identified in 12 samples, which primarily involved gains of chromosomes 4, 7, 8, 9, 12, and 20 by gains, and losses of chromosomes 10, 14, 19, and 22. Four adenomas were shown to have structural chromosome rearrangements with no apparent recurrent pattern of involvement.

Non-random trisomies of chromosomes 5, 8 and 12 in the prolactinoma sub-type of pituitary adenomas: conventional cytogenetics and interphase FISH study

Specimens from 53 pituitary adenomas (PAs), including 17 NFPA, 16 PRL-, 9 ACTH-, 9 GH- and 2 TSH-secreting tumors, underwent cytogenetic analysis by the direct and short-term culture methods. Only 8 tumors (15%) appeared to have an abnormal karyotype. To increase the resolution of cytogenetic analysis, direct preparations from 31 PAs were investigated by interphase FISH with probes specific for chromosomes 5, 8, 12 and X, for which gain in pituitary tumors has been reported. Of these 31 PAs, 17 (54.8%) had an abnormal dosage of one or more of the 4 chromosomes tested. Separate or combined trisomies of chromosomes 5, 8 and 12 were found in 10/10 prolactinomas and in 4/9 NFPA, whereas the combined loss of chromosomes 5 and 8 was observed in 1/6 ACTH- and 1/6 GH-secreting PAs. Present and earlier data on 23 PAs showed that tumors with the highest frequency of abnormal karyotypes revealed by cytogenetics and/or interphase FISH were PRL (78%), followed by NFPA (26%) and GH (18%). Recurrent structural rearrangements affecting chromosomes 1, 3 and 12 were also identified in prolactinomas, which therefore appear to be the only pituitary adenoma sub-type with a defined trend of tumor-specific chromosomal changes. Cytogenetic and FISH analyses of different pituitary tumor sub-types indicate that they may harbour genetically distinct lesions.

Molecular cytogenetics of chromosome 11 in pituitary adenomas: a comparison of fluorescence in situ hybridization and DNA ploidy study

Chromosome 11 abnormalities were detected by fluorescence in situ hybridization (FISH) technique and compared with DNA ploidy in 24 surgically removed pituitary adenomas. The tumors were diagnosed and classified by histology, electron microscopy, and pituitary hormone immunocytochemistry. They included 2 densely granulated somatotroph (DG-SM) and 4 sparsely granulated somatotroph (SG-SM) adenomas, 3 SG lactotroph (LT), 2 mixed somatotroph-lactotroph (SM-LT), 4 functioning corticotroph (CRT), 1 silent CRT subtype 1, 1 thyrotroph, 1 mixed thyrotroph-somatotroph, 2 gonadotrophs, and 4 null cell adenomas. FISH analysis with an alpha-satellite DNA probe specific for chromosome 11 showed numerical abnormalities in 16 functioning (94%) and 5 nonfunctioning (71%) adenomas. Ten functioning tumors showed aneuploid histograms, whereas the remaining and all nonfunctioning adenomas were diploid. Aberrant chromosome 11 signals were noted mostly in aneuploid adenomas involving 17% to 100% of their cell population. The severity of chromosome 11 aberrations in adenomas containing extra copies often correlated with a higher DNA index (DI). Monosomy 11 as dominant aberration was noted in a mixed SM-LT and to a lesser degree in 3 CRT adenomas involving 21% to 97% of their cell population. Two of these CRT adenomas were associated with normal DI, whereas the remaining third showed a high DI, indicating increased copy number of chromosomes other than of chromosome 11. In conclusion, chromosome 11 abnormalities are common in all types of pituitary adenomas, occurring more frequently in functioning tumors. Specific numerical abnormalities, such as monosomy and trisomy, tend to be associated with certain adenoma types, whereas tumors with extra chromosome 11 copies often exhibit aneuploid histograms.

Simple numerical chromosome aberrations characterize pituitary adenomas

Although pituitary adenomas are among the most frequent intracranial neoplasms, only very few have been cytogenetically analyzed. We have short-term cultured and karyotyped 28 consecutive pituitary adenomas (16 clinically nonfunctioning adenomas and 12 clinically functioning adenomas), finding a normal karyotype in 22, whereas 6 had clonal chromosome aberrations (5 nonfunctioning pituitary adenomas and 1 prolactinoma). The abnormal karyotypes were relatively simple. Most anomalies were numerical, with a structural rearrangement, t(6;19), being found in only one tumor. The most common aberrations were trisomy 7 (3 adenomas), trisomy 9 (2 adenomas), trisomy 12 (2 adenomas), trisomy 20 (2 adenomas), and loss and gain in 2 separate clones of one X chromosome (2 adenomas).

Cytogenetic study of pituitary adenomas

We report the results of cytogenetic studies on 23 pituitary adenoma specimens, using both the direct and short-term tissue culture methods. The direct method was applied to all of the specimens and allowed a karyotype to be identified in 15 of the processed samples (65%). Four tumors were shown to have a hypotriploid chromosomal constitution, two of which also presented structural clonal rearrangements: an isochromosome 1q,i(1)(q10) and a der(1)t(1;3)(p22;q21) were observed in two PRL-secreting adenomas, one of which also had a telomeric association involving the short arms of chromosomes 14 and 19. Telomeric associations of the long arms of chromosomes 11, 19, and 22 were observed in a near-diploid, non-secreting tumor showing monosomy 13. One other adenoma showed trisomies 8 and 12, a finding that was confirmed by means of the FISH analysis of chromosome 8 and 12 centromeric probes in the more than 300 scored nuclei. An apparently normal chromosome constitution was observed in the remaining nine cases. Short-term cultures were set up in 21 of the 23 samples, allowing us to obtain a karyotype in 18 specimens (85%). The six tumors that could not be analyzed using the direct method showed a normal karyotype. A diploid chromosome constitution was observed in the four tumors shown to be hypotriploid by the direct method as well as in the tumor with monosomy 13. The trisomies 8 and 12 identified by the direct method in one tumor were still observed, but a clone with a normal karyotype was also found. To the best of our knowledge, this is the only report of the results of cytogenetic studies on pituitary adenomas performed using both direct preparation and short-term culture.

Interphase Analysis of Chromosome 11 in Human Pituitary Somatotroph Adenomas by Direct Fluorescence In Situ Hybridization

Chromosome 11 numerical abnormalities were detected by fluorescence in situ hybridization (FISH) technique in four surgically removed pituitary somatotroph adenomas from patients clinically associated with acromegaly. The tumors were diagnosed by histology. immunocytochemistry, and electron microscopy, and included two densely granulated somatotroph (DG-SM) and two sparsely granulated somatotroph (SG-SM) adenomas. For demonstration of chromosome 11, the direct FISH technique was applied on imprints from fresh adenoma tissue fixed in acetone using an a-satellite specific centromeric probe. The slides were studied with a fluorescence microscope and the percentages of positive nuclei with aberrant fluorescent signals were counted. All tumors exhibited numerical chromosomal abnormalities in 8-23% of their cell population and included nuclei containing 1-3 extra chromosome 11 copies. The SC-SM adenomas exhibited more prominent abnormalities compared with the DG-SM adenomas. We conclude that numerical chromosome 11 abnormalities represent a frequent event among somatotroph adenomas with a tendency for higher frequency in SC-SM adenomas.

Pituitary Carcinomas

Pituitary carcinomas are defined by their metastatic growth. Most of them also invade into surrounding tissues. They should be classified by the site of their metastases (cerebrospinal, systemic, or combined) and by the presumable cell type of origin, respectively with the hormone being demonstrable by immunohistochemistry (adrenocorticotrophic hormone [ACTH], prolactin [PRL], growth hormone [GH], hormone-negative). Pituitary carcinomas develop from invasive adenomas. Nearly all tumors had been treated by surgery or X-ray before they metastasized. Since 1976, 37 cases demonstrated with modern methods were reported: 23 had metastasized into the brain or meninges, 10 showed extracerebral metastases, and 4 showed both types of metastases. In our collection of pituitary tumors, three carcinomas (0.13%) were identified: two with systemic metastases (one ACTH secreting and one PRL secreting) and one with meningeal dissemination and ACTH production. The diagnosis of pituitary carcinomas should be based on four criteria: a demonstrable metastasis, identification of the primary tumor as a pituitary tumor, similarity between the structure and immunohistological marker expression of metastasis and primary tumor, and exclusion of an alternative primary tumor.