Influência dos níveis de prolactina e tamanho tumoral na função hipofisária pós-operatória em macroadenomas hipofisários clinicamente não-funcionantes

The prolactin per unit tumor volume ratio accurately distinguishes prolactinomas from secondary hyperprolactinemia due to stalk effect

OBJECTIVE

Prolactin levels alone are insufficient to distinguish between some cases of prolactinomas and stalk effect. We aimed to (i) formally characterize the relationship between serum prolactin and prolactinoma volume, (ii) determine a cutoff for prolactin/mm³ that accurately distinguishes prolactinomas from stalk effect, and (iii) validate this cutoff in a cohort selected to include ambiguous prolactin values ranging from 50-150 ng/ml.

METHODS

We utilized the Research Patient Database Registry and transsphenoidal surgery database in our institution to retrospectively identify adult patients with clinically nonfunctioning tumors (primary analysis n=279; validation cohort n=10) and prolactinomas (primary analysis n=94; validation cohort n=18). Solid tumor volumes were measured by Visage®7 software, and cystic foci within tumors were excluded.

RESULTS

Prolactin levels correlated strongly with prolactinoma volume (r²=0.801) but were not a relevant predictor of nonfunctioning tumor size (r²=0.015). Prolactin/mm³ values did not overlap between nonfunctioning tumors (median 0.016, interquartile range [IR] 0.009-0.028) and prolactinomas (median 0.551, IR 0.265-0.845), p<0.0001. A cutoff of 0.065 (ng/ml)/mm³ correctly discriminated between prolactinomas and nonfunctioning tumors in all 401 patients in the primary analysis and validation cohort.

CONCLUSIONS

The prolactin:volume ratio correctly distinguished all prolactinomas from stalk effect in this study, including a validation cohort specifically chosen for potential ambiguity. This study is the first formal volumetric analysis of prolactin secretion in pituitary adenomas, and our results suggest that measurement of prolactin/mm³ is a valuable tool to better characterize challenging cases of primary tumoral secretion versus secondary hyperprolactinemia due to stalk effect.