Fugitive Acromegaly: A Historical, Clinical, and Translational Perspective.

The term 'fugitive acromegaly' was introduced by the neurosurgeons Bailey and Cushing in 1928 to describe subjects manifesting signs and symptoms of somatotroph hyperfunction with pituitary insufficiency. Currently, it identifies patients with subtle acromegalic dysmorphisms and inconsistent hormonal profile, possibly presenting only with hyperprolactinemia and related clinical symptoms. Patients have rapidly growing, locally invasive, relapsing pituitary macrotumors that can be classified as either acidophil stem cell tumors (ASCTs) or sparsely granulated somatotroph tumors (SGSTs), both of PIT1-lineage. ASCTs also express estrogen receptor (ER)α, show predominant prolactin (PRL) release, and less abundantly, growth hormone (GH). In contrast, SGSTs have moderately increased GH and IGF1 levels, but rarely PRL increase. ASCTs often present resistance to dopamine agonists, and long-acting somatostatin analogs are used. In contrast, SGSTs are often resistant to somatostatin analogues and instead are treated with the GH receptor antagonist pegvisomant. Differential diagnosis includes mammosomatotroph, mixed GH-/PRL-secreting, immature PIT1-lineage, and densely granulated somatotroph tumors. Studies in ER-sensitive rat tumoral mammosomatotroph cells (GH3, GH4C1) suggest that overexpression of chaperones in immature PIT1-/ER-expressing progenitors induces posttranscriptional conformational changes to tumor suppressors of the ERα and aryl hydrocarbon receptor pathways, like AIP, leading to the development of aggressive pituitary tumors like those causing fugitive acromegaly.