How Estrogen Fluctuations Before Diagnosis Affect the Size Prolactin-secreting Tumors

Plain-language summary

Prolactinomas are the most common pituitary adenomas, representing about two-thirds of clinically relevant cases. Their prevalence is around 50 per 100,000 individuals, with an incidence of 3-5 new cases per 100,000 per year and has been rising in recent decades. They may increase morbidity and mortality due to several factors: * Hormone hypersecretion: excess prolactin causes galactorrhea, amenorrhea, and infertility. * Mass effect: macroadenomas can compress adjacent structures, leading to headaches, visual loss, or neurological symptoms. * Treatment complications: medical or surgical treatments may carry risks. A marked sex difference exists, with a male-to-female ratio of 1:5-1:10, and peak diagnosis in women aged 25-44. This disparity disappears after menopause, supporting a potential role of estrogens in tumor development. Lactotrope cells, from which prolactinomas arise, are estrogen-sensitive, unlike other pituitary tumor cells (e.g., somatotrophs, gonadotrophs). A large 2022 prospective cohort (nurses) suggested a possible association between pituitary adenomas and both combined oral contraceptives (COCs) and hormone therapy (HT). However, limitations included self-reported diagnoses, lack of adenoma characterization, and contradictory findings (association with HT but not consistently with COCs). A 2009 case-control study including all adenomas found no link with hormonal contraception, while older studies from the 1980s assessed high-dose contraceptives no longer in use. Microprolactinomas are 4-5 times more frequent than macroprolactinomas (≥10 mm). Distinguishing between the two is essential, as they differ in clinical presentation, prognosis, and sex distribution. Macroadenomas are more common in men, possibly due to delayed diagnosis, as symptoms such as decreased libido are less specific, whereas women often present with amenorrhea or galactorrhea. However, studies suggest tumor size is not directly linked to symptom duration, indicating other factors may explain macroadenoma development. Why some patients develop macro- rather than microadenomas remains unclear. Estrogen exposure is a possible explanation. It is therefore relevant to investigate whether women with macroprolactinomas had greater exposure to endogenous estrogens (early menarche, late menopause, pregnancies, breastfeeding) or exogenous estrogens (contraception, menopausal HT) compared to women with microprolactinomas. The hypothesis is that women with macroprolactinomas were exposed to higher cumulative levels of estrogens before diagnosis than women with microprolactinomas.

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