To assess the proliferative activity of pituitary adenomas, 36 surgica
lly removed adenomas were studied by light microscopical parameters; m
itotic count; expression of PCNA, Ki-67, cathepsin D, and EGF; and ima
ge cytometry. Three adenomas (9%) showed high, 11 (34%) medium, 17 (53
%) moderate, and 1 (3%) low structural differentiation. In 10 adenomas
(31%), no mitosis was observed. The average was 2.4 mitoses/100 HPF;
the highest count was 7.1 mitoses/100 HPF. Eleven adenomas (33.3%) wer
e PCNA-negative; in 20 adenomas (60.6%), between 0.05 and 3.9, and in
2 adenomas (6.0%), between 10.5 and 16.4 PCNA-positive nuclei were obs
erved. Only a recurrent null-cell adenoma (9%) was Ki-67-negative. Thr
ee adenomas (9.1%) were EGF-negative, 28 (84.8%) showed up to 10% posi
tive cells, and 2 (6.1%) showed between 10 and 30% positive cells; 19
adenomas (68%) were cathepsin D-negative, including all endocrine-inac
tive adenomas. Half the adenomas had an euploid DNA stem line. Endocri
ne-inactive adenomas displayed a higher rate of euploid DNA stem lines
than endocrine-active adenomas. The S-phase fraction varied between 2
.97 and 28%, with a mean value of 14.4%. Half the adenomas showed an S
-phase fraction fo 11.65% or lower.