Growth potential of prolactinomas in men: is it really different from women?

In comparison to prolactinomas in women, those in men are usually large tumors and have been suggested to have a higher proliferation activity. To elucidate the reason for the predominance of large tumors in men, we investigated the gender-related difference of prolactinomas including growth potential.

We conducted a retrospective study comparing unselected 16 men and 27 women with prolactinoma concerning clinical and endocrine findings, tumor volume, and the mean Ki-67 (MIB-1) positive cell index (PCI).

Prolactinomas in men were larger in size (p = 0.0090), higher in serum prolactin level (p = 0.0359), and exhibited higher PCI (p = 0.0138) than those in women. However, the three factors-tumor volume, prolactin level, and the PCI-showed positive correlations with each other. There was no gender-related difference in the PCI when small tumors (<1.0 cm3) were excluded.

High PCI is associated with large tumors in both men and women. Because large tumors predominate in men, this is in fact consistent with the view that the biologic behavior of prolactinomas is different between the sexes.