Molecular Endocrine Pathology
Moderators: Dr. Ricardo Lloyd and Dr. George Kontogeorgos
Section 4 -
Molecular Pathology of Adrenal Pheochromocytomas and Extra-adrenal Sympathetic Paragangliomas
Ronald R. de Krijger, Francien H. van Nederveen, Esther Korpershoek, Winand N.M. Dinjens
Dept. of Pathology, Josephine Nefkens Institute
Erasmus MC - University Medical Center
Rotterdam , The Netherlands
Pheochromocytomas (PCC) are rare catecholamine-producing tumours of the adrenal medulla, whereas their
extra-adrenal counterparts, that share a similar histology, have been recently renamed sympathetic
paragangliomas (sPGL). The importance of the clinical and pathological recognition of PCC and sPGL lies
in two aspects. First, through their production of epinephrin and norepinephrin they cause paroxysmal
and often extreme hypertension, endangering patients' lives through an increased risk for myocardial
infarction or stroke. Second, a proportion of PCC and sPGL is malignant. The frequency of malignancy
of PCC has varied between studies, but a figure of 10% can be used as a rule of thumb. It should be
noted that sPGL have a higher frequency of malignancy, when analyzed separately.
Many investigators have tried to find distinguishing criteria, with which PCC and sPGL could be
divided in benign and malignant tumours, allowing clinicians to target the individual patient with
appropriate therapy and follow-up. A major obstacle for these studies is the small number of malignant
PCC available and the fact that PCC can only be regarded as malignant when strict criteria are applied,
i.e. the presence of histologically proven metastases, or post-operatively elevated catecholamine levels
in the presence of meta-iodobenzylguanidine (MIBG) positive lesions in sites where chromaffin tissue does
not normally occur . One of few studies that do not suffer from the abovementioned drawbacks has
proposed a new scoring system, the so-called "Pheochromocytoma of the adrenal gland scaled score" . A
more recently advocated scoring system is that proposed by Kimura et al. . Both systems await
further confirmation. Another promising area is that of the telomeric complex, where independent
confirmation from several groups suggests that upregulation of certain proteins or enzymes occurs in
malignant vs. benign PCC
Attention has also been directed at the proliferative activity of PCC.
Several studies have shown a correlation between the percentage of cells in the cell cycle, determined by
MIB1 labelling, and the clinical behaviour of PCC
Malignant PCC as a group have a higher
labelling index than benign PCC.
As clinical and pathological parameters did not yield one or more clinically applicable distinguishing
criteria, molecular studies have attempted to provide such criteria. Briefly, these can be divided into
two categories: those using a candidate gene approach and those using more global genome-based methods.
Candidate gene analysis.
As PCC and sPGL are known to occur in the context
of several inherited endocrine tumour syndromes, much attention has been focussed on the disease-causing
genes that have been discovered over the past decade. In multiple endocrine neoplasia type 2 (MEN2),
activating mutations in the RET proto-oncogene on 10q11.2 are responsible for the genesis of medullary
thyroid carcinomas in virtually 100% of patients and PCC/sPGL in 50%. Von Hippel-Lindau (VHL) disease is
caused by a variety of inactivating mutations or aberrations in the VHL gene on 3p25, whereas three genes
of the succinate dehydrogenase complex (SDHB, SDHC, and SDHD) have been implicated in the genesis of the
so-called pheochromocytoma-paraganglioma (PCC-PGL)
syndrome . Together, mutations in one of these
genes appear responsible for at least 10%, but possibly up to 25%, of PCC or sPGL, with many apparently
sporadic cases in fact being hereditary
. Apart from this, the frequency of somatic mutations of
each of these genes has been investigated, but it appeared that only a small proportion of truly sporadic
PCC had somatic RET or VHL mutations, whereas somatic mutations in the SDH genes are rare or non-existent
While no loss of heterozygosity (LOH) studies
addressed differences between benign and malignant PCC, comparative genomic hybridisation (CGH) analysis
showed differences between various groups of PCC, including familial vs. sporadic PCC, and also between
benign vs. malignant PCC
Apart from the number of chromosomal changes, that is significantly
different between benign and malignant PCC, selected regions were differentially lost in malignant PCC,
including 6q, 8p, and 18p, or differentially gained, including 5p, 7p, and 12q. Recently, an LOH
analysis-based study has been published, showing that PCC in general have a high frequency of 6q loss
. The overlap between the two groups of tumours and the laborious CGH procedure has prevented the
development of this finding into a clinically useful test. Recently, more detailed CGH analysis
techniques have been developed, so-called array-CGH, which allow detection of chromosomal changes with
superior resolution. In this context, we have studied 1p in detail, showing that there might be several
regions of minimal loss pointing toward the existence of multiple candidate tumor suppressor genes .
Furthermore, Jarbo et al. have shown a high frequency of 22q deletions in sporadic PCC . Clearly,
the results from conventional CGH need confirmation and will be subject to modification as a result of
this technological improvement.
Another major technological advancement represents expression profiling analysis, which has become
available over the past years. This technique allows analysis of the expression level of the majority of
genes and comparisons of gene expression can be made between various groups of tumours, including benign
and malignant PCC. These so-called "gene chips" have been used for the discrimination of breast cancers
with differing prognosis, allowing targeted chemotherapy, but also for the discrimination of various
types of leukaemia, lymphoma, and sarcoma, which could not be discriminated by histology and
In these studies, a relatively small gene set, between 50 and 100
genes, could discriminate between various prognostic groups. For PCC, few studies have been published so
far, and none have addressed the issue of benign vs. malignant PCC. It appears, however, that PCC can be
divided into at least two groups, those with a VHL signature, linked to the hypoxia-angiogenesis pathway,
and those with an MEN2 signature , in line with previous CGH data. While these data are
predominantly based on familial tumours with VHL or RET mutations, it appears that also sporadic tumours
fall into at least two groups, when analysed with the CGH technology (van Nederveen et al., unpublished
The current status of molecular knowledge about the genesis of PCC and sPGL is as follows:
- Depending on the investigated population, between 10 and
25% of PCC and sPGL is caused by germline mutations in one of four genes (RET, VHL, SDHB, and SDHD)
- Somatic mutations in these genes do not appear to play a
major role in the genesis of truly sporadic PCC and sPGL
- Conventional and array-CGH have indicated that potential
tumour suppressor genes involved in benign PCC and sPGL are located on 1p, 3p, 3q, and 11p
- Discrimination of benign and malignant PCC and sPGL
appears feasible by CGH, though not yet clinically applicable
- Gene expression profiling stalludies are awaited for further
discrimination between benign and malignant PCC and sPGL and should be combined with CGH data
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