Objective: To explore the basis of the gender-based differences in endocrine and surgical findings in patients with prolactinoma (prolactin cell adenoma) as well as in their clinical outcome. Material and Methods: In young or reproductive-age female patients, older women (beyond 40 years of age), and male patients, we systematically studied the following factors: operative and endocrine features (tumor size, invasiveness, preoperative serum prolactin level, and biochemical outcome), specific biologic variables (mitotic index, MIB-1 labeling index, and p27 immunoreactivity), and hormone receptor status (estrogen and progesterone receptor proteins as well as dopamine D2 receptor messenger RNA). Results: Of the various factors assessed, the preoperative prolactin level and MIB-1 labeling index were lower in young female patients in comparison with older female and particularly male patients. Hormone levels were also positively associated with mitotic activity as well as the MIB-1 labeling index. Although invasion was infrequent in microadenomas of young female patients, no statistically significant differences in tumor size or invasiveness were noted among the three patient groups. Absence of differences in invasiveness may, in part, be explained by artifacts of case selection. Conclusion: The basis for the observed differences in proliferative activities in tumors of the three study groups is not readily apparent but may reflect differences in the endocrine milieu or the effect of sex steroid hormone receptors, tumoral vascularity, or specific growth factors.
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