Thymic Neuroendocrine Tumors and Cushing's Syndrome

Ectopic ACTH Sources and Thymic Involvement

Elevated ACTH levels indicate that excessive cortisol secretion is not originating from the adrenal gland itself but from other sources such as pituitary tumors or ectopic tumors, according to the National Comprehensive Cancer Network 1
Ectopic ACTH-producing tumors can be found in various locations including the lung, thyroid, pancreas, bowel, and importantly, the thymus, as reported by the National Comprehensive Cancer Network 1
Up to 2% of patients with Cushing's syndrome have it caused by ectopic ACTH production from thymic neuroendocrine tumors, as stated by the European Society for Medical Oncology 2
Thymic carcinoids (neuroendocrine tumors of the thymus) are rare with an overall age-adjusted incidence of 0.02/100,000/year but are established sources of ectopic ACTH, according to the European Society for Medical Oncology 2

When Cushing's syndrome is suspected, the diagnostic approach should include confirmation of hypercortisolism through 24-hour urine cortisol, late night salivary cortisol, or dexamethasone suppression testing, as recommended by the Endocrine Society 3, 4
Measurement of plasma ACTH to determine if the hypercortisolism is ACTH-dependent is crucial, according to the Endocrine Society 3
Bilateral inferior petrosal sinus sampling (IPSS) with CRH stimulation helps differentiate between pituitary and ectopic sources of ACTH, as suggested by the Endocrine Society 3
Somatostatin receptor imaging such as 68Ga-DOTATATE PET can be valuable for localizing ectopic ACTH-producing tumors including those in the thymus, as recommended by the Endocrine Society 3

Medical management with adrenostatic agents such as ketoconazole and mitotane can be used to control hypercortisolism, as suggested by the National Comprehensive Cancer Network 1
Bilateral adrenalectomy may be considered for patients with unresectable ectopic ACTH-producing tumors, according to the National Comprehensive Cancer Network 1
Octreotide can be considered if the tumor is Octreoscan-positive, although it may be less effective for controlling ectopic ACTH secretion than in other contexts, as reported by the National Comprehensive Cancer Network 1

Thymic carcinoid tumors may rarely cause carcinoid syndrome (in about 2% of cases), and carcinoid crisis can occasionally occur following surgical manipulation, as stated by the European Society for Medical Oncology 2
These tumors may be part of Multiple Endocrine Neoplasia type 1 syndrome (MEN-1) in 5-15% of cases, according to the European Society for Medical Oncology 2