Endocrine effects of non-endocrine tumors

Paraneoplastic Syndromes - Hormones Rogue

Tumors producing hormones not native to their tissue of origin, causing systemic effects.

• Ectopic ACTH (Cushing Syndrome):
  • Source: Small Cell Lung Cancer (SCLC), pancreatic cancer.
  • Effect: ↑Cortisol → Cushingoid features, hypertension, hypokalemia.
• Ectopic ADH (SIADH):
  • Source: SCLC, CNS tumors.
  • Effect: ↑ADH → Hyponatremia, ↓serum osmolality.
• PTH-related peptide (PTHrP):
  • Source: Squamous Cell Lung Cancer, Renal/Bladder/Breast Ca.
  • Effect: Hypercalcemia (mimics hyperparathyroidism).
• Ectopic Erythropoietin (EPO):
  • Source: Renal Cell Carcinoma, Hepatocellular Carcinoma.
  • Effect: Polycythemia.

⭐ Small Cell Lung Cancer (SCLC) is the most common cause of both ectopic ACTH and ADH production, making it a classic culprit for multiple paraneoplastic syndromes.

Ectopic Cushing & SIADH - Small Cell's Double Trouble

• Small Cell Lung Cancer (SCLC) is notorious for paraneoplastic syndromes via ectopic hormone production.

• Ectopic Cushing Syndrome:

  • Cause: Ectopic ACTH secretion.
  • Features: Rapid onset hypertension, hypokalemic metabolic alkalosis, and hyperglycemia. Classic cushingoid signs (e.g., moon facies) are often absent.
  • Diagnosis: ↑ ACTH & cortisol levels that are not suppressed by a high-dose dexamethasone test.

• SIADH (Syndrome of Inappropriate ADH):

  • Cause: Ectopic ADH secretion.
  • Features: Euvolemic hyponatremia with ↓ serum osmolality (<275 mOsm/kg) but ↑ urine osmolality (>100 mOsm/kg).

⭐ High-Yield: The most common paraneoplastic syndrome associated with SCLC is SIADH, while ectopic Cushing syndrome is the second most common endocrine manifestation.

Hypercalcemia of Malignancy - Bone Breakers

• Most common paraneoplastic syndrome. Presents with "stones, bones, groans, thrones, psychiatric overtones."
• Primary Mechanisms:
  • Humoral (HHM): Accounts for ~80% of cases. Mediated by parathyroid hormone-related protein (PTHrP).
    • Mimics PTH: ↑ bone resorption, ↑ renal Ca²⁺ reabsorption.
    • Associated Tumors: Squamous cell (lung), renal, bladder, breast, ovarian.
  • Local Osteolysis: Direct bone destruction from metastases (e.g., breast cancer, multiple myeloma) releasing osteoclast-activating cytokines.
  • Ectopic Vitamin D: Rare. Tumor production of $1,25-( ext{OH})_2 ext{D}_3$ (calcitriol), seen in lymphomas.

⭐ In Humoral Hypercalcemia of Malignancy, labs show ↑ serum Ca²⁺ and ↑ PTHrP, but endogenous PTH is suppressed (↓ PTH).

Other Notable Syndromes - The Rare Rebels

• Stauffer Syndrome: Paraneoplastic hepatic dysfunction (non-metastatic) seen in Renal Cell Carcinoma (RCC).

  • Features: Fever, hepatosplenomegaly, ↑ ALP, ↑ ESR, ↑ prothrombin time.
  • Mechanism: Likely cytokine-mediated (e.g., IL-6); resolves after nephrectomy.

• Hypertrophic Osteoarthropathy: Triad of digital clubbing, arthritis, and periostitis of long bones.

  • Strongly associated with non-small cell lung cancer (especially adenocarcinoma).

• Polycythemia: Ectopic erythropoietin (EPO) production leading to ↑ RBC mass.

  • Associated tumors: Renal Cell Carcinoma, Hepatocellular Carcinoma, Cerebellar Hemangioblastoma.

⭐ Trousseau Syndrome (Migratory Thrombophlebitis): Superficial venous thromboses appearing in different locations over time. It is a classic sign of visceral malignancy, particularly mucin-producing adenocarcinomas of the pancreas or lung.

High‑Yield Points - ⚡ Biggest Takeaways

• Ectopic Cushing syndrome is most often from small cell lung cancer (SCLC) secreting ACTH.
• SIADH, causing hyponatremia, is also commonly associated with SCLC.
• Hypercalcemia, the most frequent syndrome, is often due to PTHrP from squamous cell lung cancer.
• Hypoglycemia can be caused by tumors overproducing IGF-2, like hepatocellular carcinoma.
• Polycythemia can result from ectopic EPO production by renal cell or hepatocellular carcinomas.
• Carcinoid syndrome (flushing, diarrhea) is due to serotonin from metastatic carcinoid tumors.