Prolactinomas in women commonly present as small intrasellar
tumors, but are usually much larger in men. This discrepancy has generally been attributed to differences in the delay before diagnosis. However, studies comparing clinical and pathological correlates of growth of these
tumors in both sexes are lacking. We conducted a retrospective study comparing 45 men and 51 women bearing
prolactinoma to determine whether the predominance of large
tumors in men was due to a delay in diagnosis or, rather, to a fundamental sex-related difference in
tumor growth. Basal PRL levels (mean +/- SEM, 2789 +/- 573 ng/mL) and mean
tumor diameter (26 +/- 2 mm) were significantly higher in men than in women (292 +/- 74 ng/mL and 10 +/- 1 mm, respectively; P < 0.001), but were not correlated to the age at diagnosis or the duration of symptoms. Giant
tumors (n = 8) occurred in males only. The frequencies of
bromocriptine-resistant
tumors (30 vs.5%; P < 0.01) and invasive macroadenomas (52 vs.27%; P < 0.001) were significantly greater in men than those in women. Lastly,
macroprolactinomas in males exhibited higher indexes of proliferating cells by Ki-67 immunoreactivity (2.6 +/- 1.1% of positive nuclei) than did similar
tumors in female patients (0.4 +/- 0.2%; P = 0.08). We conclude that the predominance of large
prolactinomas in men is due to a high frequency of rapidly growing
tumors, which are often invasive and frequently
bromocriptine resistant.