Proving the Source: Tests, Scans, and Your Pathology Report

Proving that a pancreatic tumor is responsible for your cortisol excess is a complex, multi-step “detective” process. Because the symptoms of Cushing syndrome are the same whether the cause is a tiny growth in the brain (pituitary) or a tumor in the pancreas, doctors must follow a current specialist-guideline pathway to confirm the source before they can properly treat it ^[1][2]. Testing is highly individualized, and you may not follow these exact steps in order.

Step 1: Proving the Cortisol Excess

The first goal is to prove your body is making too much cortisol. Your team likely used these three standard tests:

• 24-Hour Urinary Free Cortisol (UFC): You collect all urine for 24 hours to measure total cortisol production ^[3]. In ectopic cases, this number is often 10 times higher than the upper limit of normal ^[4].
• Late-Night Salivary Cortisol (LNSC): Cortisol should be at its lowest around midnight. If it remains high in your saliva at night, it confirms the “clock” for your hormone production is broken ^[5].
• Low-Dose Dexamethasone Suppression Test (LDDST): You take a small steroid pill (dexamethasone) at night. A healthy body reacts by shutting down its own cortisol production. If your levels stay high, it suggests autonomous (uncontrolled) production ^[2].

Step 2: Finding the Source (Pituitary vs. Ectopic)

Once high cortisol is confirmed, doctors check your ACTH (adrenocorticotropic hormone) levels. High ACTH means the problem is “ACTH-dependent.” To assess whether the ACTH is coming from the pancreas and not the pituitary gland, they may use:

• High-Dose Dexamethasone Suppression Test (HDDST): Similar to the low-dose test, but using a much higher dose. Pituitary tumors sometimes lower their cortisol in response, while ectopic tumors usually ignore it. However, this test has limited accuracy and is rarely a definitive standalone test ^[6].
• BIPSS (Bilateral Inferior Petrosal Sinus Sampling): If imaging is unclear, a specialized radiologist threads tiny catheters to the veins draining the pituitary gland to measure ACTH directly. It assesses the central-to-peripheral ACTH gradient. While highly accurate, it is invasive and may be unnecessary when other biochemical and imaging evidence is convincing. If the ACTH levels in the brain are low but the levels in the rest of your body are high, it strongly suggests the source is ectopic (outside the brain) ^[7][8].

Step 3: Mapping the Tumor with Imaging

Standard CT or MRI scans may find the tumor, but specialized scans are often needed to see the full picture:

• Ga-68 DOTATATE PET/CT: This scan uses a tracer that “sticks” to somatostatin receptors (SSTR) often found on neuroendocrine cells ^[9].
• FDG PET/CT: If the DOTATATE scan is negative, it might mean the tumor is more aggressive, but can also result from low receptor expression, small lesions, or tumor heterogeneity. FDG PET/CT provides complementary information by measuring glucose uptake, helping find “faster-growing” cells ^[10][11].

Step 4: Decoding Your Pathology Report

If you have had a biopsy or surgery, your pathology report is the most important document in your care. It tells your team exactly how “aggressive” the cells are.

Understanding the Grade and Ki-67

Doctors use two main numbers to grade the tumor ^[12]:

1. Ki-67 Index: This is a percentage that tells you how many cells are currently dividing. A Ki-67 under 3% is Grade 1 (slowest), 3–20% is Grade 2, and over 20% is Grade 3 ^[13]. It must be interpreted with mitotic rate, necrosis, and morphology.
2. Mitotic Rate: A manual count of how many cells are caught in the act of dividing under a microscope ^[12].

NET vs. NEC: The Most Important Distinction

• Well-Differentiated (NET): The cells still look somewhat like normal pancreatic cells. These can be G1, G2, or even G3 (well-differentiated G3) ^[14].
• Poorly Differentiated (NEC): The cells look very abnormal and aggressive. This is called a Neuroendocrine Carcinoma (NEC) and requires a different treatment approach ^[15].

The Role of Staining

The pathologist uses special dyes to identify the cells:

• Chromogranin A & Synaptophysin: These “stains” confirm the cells are neuroendocrine in nature ^[16].
• ACTH Staining: This looks for the hormone inside the tumor cells. Crucially, tissue immunostaining can be technically variable, and a negative ACTH stain does not always mean the tumor isn’t the cause. Sometimes the tumor releases the hormone so fast it doesn’t “store” enough to show up on the stain, or it might be producing a precursor called POMC that the standard ACTH stain can’t see ^[17].

Pathology Completeness Checklist

Ensure your report includes these vital pieces of information:

• Differentiation: (Well-differentiated NET vs. Poorly differentiated NEC) ^[14][15]
• Grade: (G1, G2, or G3) ^[12]
• Ki-67 Index: (The exact percentage) ^[13]
• Hormone Markers: (Chromogranin A, Synaptophysin, and ACTH/POMC) ^[16][17]