Tumour suppressor genes in pituitary tumour formation

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.

Downregulation of putative tumor suppressor gene TSC-22 in human brain tumors

BACKGROUND AND OBJECTIVES

Our objective was to identify differentially expressed genes involved in the pathogenesis of glioblastoma multiforme (GBM).

METHODS

Screening of arrayed human fetal brain and human postnatal brain cDNA libraries was performed by differential hybridization with glioblastoma multiforme and human normal brain cDNAs.

RESULTS

Repeated differential hybridization of more than 100 cDNA clones selected by primary screening and analysis of RNA from adult normal brain and glial tumors showed 16 nucleotide sequences differentially expressed between normal brain and brain tumors. Among others, decreased content in astrocytic tumors was determined for TSC-22 mRNA corresponding to cDNA in the ICRFp507J1041 clone from human fetal brain cDNA library. Northern blot hybridization of RNA from different human brain tumors showed very low amounts of TSC-22 mRNA in most investigated samples of GBM, anaplastic astrocytoma, and some other tumors. Complete lack of expression of TSC-22 occurred in one sample of anaplastic astrocytoma, as well as in meningioma, brain sarcoma, sarcomatous meningioma, and oligodendroglioma. The differential expression of TSC-22 gene was confirmed by semiquantitative RT-PCR in 15 samples of astrocytomas WHO grade II-IV and three samples of normal brain.

CONCLUSIONS

Significantly decreased levels of TSC-22 mRNA in human brain and salivary gland tumors and antiproliferative role of TSC-22 strongly suggest a tumor suppressor role for TSC-22. J.

Classification of pituitary adenomas

This brief review summarizes various schemes which were introduced to classify pituitary tumors of adenohypophysial origin. Many different classifications were proposed. Pathologists prefer classifications based on the morphologic features of tumor cells. The gold standard is the light microscopic study of hematoxylin-eosin stained sections of formalin fixed and paraffin-embedded tissues. For correlation between hormone production, secretory activity and cytogenesis, immunohistochemical and transmission electron microscopic investigation is needed. We are convinced that in the future, molecular and genetic techniques will also be applied. We present here our five-tier scheme for classification of pituitary tumors which was accepted by the 'World Health Organization International Histological Classification of Tumours'. This classification takes into consideration the clinical and laboratory findings, imaging results, histologic, immunocytochemical and ultrastructural features of tumor cells. Despite several recent attempts to assess the growth rate, aggressiveness and invasiveness of pituitary tumors, more work is required to draw conclusions on their prognosis.