Pituitary adenomas: tumor cell growth by cluster formation. Pattern analysis based on immunohistochemistry.

The topographical distribution of adrenocorticotropic hormone, growth hormone and prolactin was studied in nine multihormonal pituitary adenomas and two normal adenohypophyses using quantitative immunohistochemical methods. For each pituitary hormone paraffin sections stained by antihormone antibodies were scanned with a light microscope equipped with a projection and scanning device. The number of immunoreactive cells of each square in the grid was counted and transformed into pseudocolors. In this way, the distribution of each hormone was documented. A chi-square test was applied to these distribution patterns to prove randomness. A nonrandom distribution of immunoreactive cells was observed in all pituitary adenomas and normal pituitary glands. Cluster formations of immunoreactive cells were found for each hormone. The clusters were surrounded by halo-like areas of decreasing number of immunoreactive cells from center to periphery. The cluster-halo type of immunoreactive cells was found not only in the adenomas but also in the normal pituitary gland. This may be explained by the similarity of biological processes during cell proliferation either in normal development or in adenoma formation. It can be concluded from our studies that pituitary adenomas in most cases develop by multicentric but not diffuse proliferation of cell clones of different endocrine activity.