Severe Cyclical Hypercortisolism Due to Metastatic Neuroendocrine Cancer Initially Diagnosed as Colon Cancer

Case Description: A 65 year-old male with initial diagnosis of metastatic colon cancer based on liver biopsy presented for evaluation of severe hypercortisolism with 24-hour urinary free cortisol (UFC) of 1184 mcg/day after presenting to his Oncologist in December 2019 requesting evaluation for muscle weakness and weight gain. On re-evaluation in March, his cortisol had dramatically improved with 24-hr UFC of 120 mcg/day and ACTH of 84 pg/mL and had resolved with 24-hr UFC of 32.6 mcg/day by May. A 2 cm pancreatic lesion was noted during cancer staging; a second opinion was obtained on the liver biopsy which was interpreted as metastatic neuroendocrine tumor, possibly of pancreatic origin. The patient was started on FOLFINIRNOX in December 2019. This was transitioned to carboplatin and etoposide after the revised diagnosis and was continued through May with regression of liver lesions on followup imaging. A 68 Ga-DOTATATE PET CT confirmed uptake in the pancreas, retroperitoneal lymph nodes, and thyroid. A thyroid ultrasound was obtained which did not meet FNA criteria. Given the chronologic association between cortisol levels and chemotherapy response we were suspicious for ectopic Cushing’s syndrome due to metastatic neuroendocrine cancer and the patient was followed for recurrence. In September, the patient endorsed leg weakness and hyperglycemia and was found to have a 24-hr UFC of 4731 mcg/day and an 8 am cortisol of 102 mcg/dL. The patient developed severe hypokalemia requiring admission and was restarted on chemotherapy with moderate improvement in cortisol levels and symptoms. Given the degree of cortisol elevation, we recommended bilateral adrenalectomy, for which the patient established care at a more specialized center. Discussion: Ectopic Cushing’s syndrome is an uncommon variety of ACTH-dependent Cushing’s syndrome caused by CRH or ACTH-producing tumors. The more aggressive form is associated with small-cell lung cancer while the chronic form is associated with indolent tumors. Cyclical Cushing’s syndrome is a rare cause of hypercortisolism characterized by cyclical variations in cortisol levels. The pathophysiology of the cyclical variation is unclear. About half of cases are caused by pituitary corticotrophs but up to 26% can be attributed to ectopic ACTH production, typically due to indolent tumors rather than aggressive malignancies. We present a case of cyclical hypercortisolism with an initial diagnosis of colon cancer. On further review, the cyclical hypercortisolism was likely associated with chemotherapy response. Reevaluation of surgical pathology was consistent with metastatic neuroendocrine cancer, the likely source of ectopic ACTH. Our case highlights the importance of maintaining a broad differential when considering cases of cyclical cortisol elevation, including consideration of concurrent chemotherapy for seemingly unrelated malignancies.