Role of cell and explant culture in the diagnosis and characterization of human pituitary tumours

Summary

The pattern of hormone secretion by human pituitary tumours in cell or explant culture has been shown to be of value in establishing the nature of the tissue. There was complete agreement between the diagnosis reached by conventional immunocytochemical techniques and by examining the secretion of hormones in culture. Culture techniques, however, have some advantages over immunocytochemical analysis. In particular, immunocytochemical techniques can only be used to examine a small, possibly unrepresentative, portion of the pituitary tissue, whereas the in vitro culture systems make use of the whole tissue. In addition, in vitro culture is simpler to employ and can be carried out relatively rapidly. Cell and explant culture was therefore used to examine the nature of human pituitary tumours.

To determine the incidence of mixed GH-PRL secreting pituitary tumours in acromegaly, the pattern of hormone secretion in vitro by 98 somatotrophic tumours was examined. Thirty-seven per cent were found to be pure somatotrophic tumours and 59.2% secreted both GH and PRL, but no other hormone, indicating that these tumours were of mixed nature. This latter group could be divided into those removed from patients with hyperprolactinaemia (35.7% of all tumours) and those from patients with normal pre-operative serum PRL levels (23.5%). A further small group (3.1%) of tumours secreted only GH in culture, despite elevated pre-operative serum PRL levels, indicating that the hyperprolactinaemia in these patients was due to pituitary stalk compression by the somatotrophic tumour, thereby preventing prolactin release inhibiting factor reaching the lactotrophs and allowing uncontrolled PRL secretion.

Pituitary tumours, pre-operatively diagnosed as ‘functionless’ could be classified on a secretory basis, most producing gonadotrophins (57.3%), whilst 7.3% secreted GH, 8.5% secreted PRL and 1.2% secreted ACTH. Presence or absence of PRL secretion by ‘functionless’ tumours was correlated with 88 patients whose pre-operative serum PRL was measured. The findings indicated that, in this series, 12.7% of tumours diagnosed as ‘functionless’ were, in fact, prolactinomas. Additionally, 18.3% of ‘functionless’ tumours failed to secrete PRL in vitro but were removed from patients with elevated PRL levels. These results suggest that the pre-operative hyperprolactinaemia in these cases was due to compression of the pituitary stalk by the tumour. It is concluded that in vitro pituitary culture techniques can be used to diagnose and characterize the nature of pituitary tumours.