A study examining the genes expressed in pituitary tumors of Cushing’s disease patients found that these tumors may be grouped into three distinct subsets.
The finding suggests that different biological processes contribute to the development of each subset, an insight that may aid in developing targeted therapies.
The study, “Gene expression profiling in human corticotrope tumors reveals distinct, neuroendocrine profiles,” was published in the Journal of Neuroendocrinology.
In Cushing disease, a pituitary tumor producing excess amounts of the adenocorticotropic hormone causes the body to produce too much cortisol.
Pituitary tumors respond differently to modulators of ACTH secretion, and patients have different disease manifestations, but what makes them differ from one another is unknown.
To determine if the genetic profile of tumors could explain the clinical diversity reported in these patients, Italian researchers evaluated 40 benign, ACTH-secreting pituitary tumors removed from patients with Cushing’s disease.
Of the 20,815 genes examined in the study, 1,259 were significantly elevated in the pituitary tumors. These were mostly involved in pathways that kept the neuroendocrine cell profile.
Based on their genetic profile, researchers were able to cluster tumors into three distinct subgroups. Samples in group A had four specific genes, associated with tumor-related processes, that were overly active. In group B, there were 313 overly active genes, involved in many of the mechanisms of hormone-secreting adenomas.
Group C had 29 highly active genes, all involved in calcium influx and cell growth – mechanisms that are important for the development of ACTH-secreting adenomas.
“It appears that these tumors present a neuroendocrine cell profile but, at the same time, clearly distinct gene expression patterns [are seen] in individual subgroups,” the researchers wrote.
Looking at clinical characteristics that correlated with each subgroup, the researchers found that most group A patients had macroadenomas (large tumors) that had invaded the sella – the compartment where the pituitary gland resides at the base of the brain. These patients were also older than those in the other two subgroups.
Some patients in group B also had macroadenomas, but no such tumors were seen in group C. However, researchers found no association between the groups and the hormonal values, clinical findings, or surgical outcomes.
Collectively, the findings add new clues to the molecular mechanisms involved in the progression of benign pituitary tumors. They also provide new ground for developing targeted therapies, the researchers said.