General Flashcards
What are the different types of anterior pituitary tumors and how do they differ in terms of hormone secretion and clinical presentation? Classification?
Most pitatuary tumers are bening adenomas. They are classified depending of the hormones produced by the neoplastic cell
- Functional: Hormone producing
- Non functional: Non hormone producing. They are usually found in late state and are often macroadenomas. Due to their size they might destroy the adjacent paranchyma and cause hypopituitarism.
- Silent: Produces hormones on tissue level and does not have clinical presentation
Both functional and non functional are usually composed of one cell type, but some can secrete two different hormones (Growth hormones and prolactine being the most common combination). They are rarely plurihormonal. They are called microadenomas if they are less than 1cm in diameter and macroadenomas if they are larger than 1cm.
What is the role of G-proteins in pituitary adenomas?
Mutation in this gene in one of the most common chaninges in pituatary adenomas.
How does activation of Gsα affect cellular proliferation in the pituitary gland?
Activation of Gsα results in the generation of cAMP, which is a potent mitogenic stimulus in several endocrine cells, promoting cellular proliferation and hormone synthesis and secretion
What is the significance of GNAS mutations in pituatary adenomas?
GNAS has a role in encoding the α subunit of the G-protein and mutation in that gene abrogate the GTPase activity of Gsα, leading to constitutive activation of Gsα, persistent generation of cAMP, and unchecked cellular proliferation.
What molecular abnormalities are associated with aggressive behavior in pituitary tumors?
Molecular abnormalities associated with aggressive behavior include aberrations in cell cycle checkpoint genes, such as overexpression of cyclin D1, mutations of TP53, and epigenetic silencing of the retinoblastoma gene (RB). In addition, activating mutations of the RAS oncogene are observed in rare pituitary carcinomas.
How can mutations in cell cycle checkpoint genes lead to uncontrolled cell growth?
Mutations in cell cycle checkpoint genes, such as TP53 and the retinoblastoma gene (RB), can lead to uncontrolled cell growth by allowing cells to bypass the normal checks and balances that prevent excessive cell division.
What is the usual composition of a pituitary adenoma?
Pituitary adenomas are composed of relatively uniform, polygonal cells arrayed in sheets, cords, or papillae with sparse supporting connective tissue or reticulin. The lesion is usually well-ceicumscribed and soft lesion.
How do larger pituitary adenomas affect adjacent structures?
Larger pituitary adenomas may compress the optic chiasm and adjacent structures, erode the sella turcica and anterior clinoid processes, and extend locally into the cavernous and sphenoidal sinuses.
Is the tumor encapsulated or nonencapsulated?
30% of the cases its nonencapsulated and infiltartes adjacent bone, dura and brain (but its common)
What distinguishes pituitary adenomas from non-neoplastic anterior pituitary parenchyma?
The cellular monomorphism and the absence of a significant reticulin network distinguish pituitary adenomas from non-neoplastic anterior pituitary parenchyma.
What is the functional status of an adenoma predicted from its histologic appearance?
The functional status of the adenoma cannot be predicted from its histologic appearance.
What distinguishes atypical adenomas from other adenomas?
Adenomas that harbor TP53 mutations often demonstrate brisk mitotic activity and higher proliferation rates and are designated atypical adenomas because of their potential for aggressive behavior.
