Endocrine Abstracts

Clinically non-functioning pituitary adenomas (NFA) are common anterior pituitary tumours, arising from a variety of pituitary cell types, but little is known of their pathogenesis. The vast majority of NFA are benign tumours; some of which may remain intrasellar, while others may exhibit expansive extrasellar growth and/or become invasive and infiltrate dura and bone. Pituitary carcinoma, defined as a tumour with subarachnoid, brain or systemic metastases is very rare. Determination of predictive factors for aggressive behaviour would enable appropriate treatment and follow-up to be tailored to the patient.

Tumours can be considered to be displaying aggressive behaviour in different ways; for example malignant transformation is rare, in contrast to invasive tumour growth. Unlike other tumour types, complications due to excess hormone production are, by definition very unusual, although occasionally seen in association with progression of silent ACTH tumours. There are marked differences in tumour growth between those NFA that exhibit rapid expansion and mass effects, contrasting with incidentally detected NFA which may show little change during serial imaging. Tumours that regrow following surgery, and less frequently following post-operative radiotherapy illustrate aggressive tumour behaviour.

Determination of predictive factors for aggressive behaviour has been the goal of many clinical and laboratory studies. These have included assessment of tumour characteristics such as proliferation (e.g. Ki-67 labelling), markers of the cell cycle (e.g. cyclin and regulatory kinin expression), angiogenesis and differences in growth factor (e.g. FGF) or receptor expression. Accumulation of genetic aberrations has been shown in some but not all aggressive NFA. Studies investigating the predictive significance of patient and tumour characteristics (histological subtype, invasiveness, apoplexy, post-operative appearance) often show conflicting results. Thus at present there is a lack of reliable consistent prognostic factors for aggressive NFA behaviour.