Introduction. Ki-67 is a marker of proliferation activity associated with invasiveness and prognosis in human tumours.

Aim of the study. to evaluate the Ki-67 index prognostic relevance in a group of acromegalic patients who underwent transsphenoidal surgery for a GH-secreting pituitary adenoma.

Material and methods. We selected 68 consecutive acromegalic patients referred to our hospital during a 5-years period. The Ki-67 index was determined by immunohistochemistry on tissue samples obtained from each adenoma after surgery. Those patients who were not completely cured after surgery begun medical therapy with somatostatin analogs (SSA). Periodical pituitary MRI and hormonal evaluation were performed during the follow-up.

Results. Twenty-eight out of 68 patients were cured after surgery (41%). Among the 40 patients treated with SSA, 13 were considered as uncontrolled. Pituitary MRI showed residual/recurrent disease in 25 out of 68 patients after 6 months. No correlation was found between Ki-67 index and age, tumour size, GH or IGF-I plasma levels. Tumours described as having cavernous sinus invasion had a higher mean Ki-67 index as compared to non-invasive tumours (p<0.01). The Ki-67 index was significantly lower in tumours in patients cured after surgery as compared to patients considered as not cured (p<0.01) and in tumours in patients controlled by SSA therapy as compared to patients considered as uncontrolled (p<0.05).

Conclusion. The Ki-67 labelling index may predict clinical outcome in post-surgical management of acromegalic patients. We suggest routinary Ki-67 evaluation in GH-secreting pituitary adenomas.