dromlakhani GAPP Score Application for PPGL Metastasis Risk Assessment
STEP 1 — Gather Information
Obtain formalin-fixed paraffin-embedded tumor slides and pathology report; document presence of necrosis, vascular invasion, and mitotic count per 10 high-power fields (HPF).
STEP 2 — Rule In / Rule Out
If adequate tumor tissue is available for histopathological evaluation, proceed to scoring; otherwise, the GAPP score cannot be applied and alternative risk assessment methods should be considered.
STEP 3 — Classify or Stratify
Assign points: necrosis (0‑2), vascular invasion (0‑2), mitotic count (≥5/10 HPF = 1 point); sum to obtain GAPP score (0‑5). Stratify risk: low (0‑2), intermediate (3‑4), high (5).
STEP 4 — Decide
For high GAPP score (≥5), recommend intensified surveillance (e.g., contrast-enhanced MRI or 18F‑FDG PET every 6 months) and consider genetic testing for SDHB; for low/intermediate scores, follow standard postoperative surveillance (annual biochemical testing and imaging every 1‑2 years).
Clinical Guardrails / Mimics / Pitfalls
Requires expert pathology assessment; avoid using GAPP score alone without clinical context; do not substitute for genetic testing; be aware of inter‑observer variability and sampling error in small biopsies.
Concrete Clinical Example
A 48‑year‑old with an adrenal PPGL shows focal necrosis (1 point), focal vascular invasion (1 point), and mitotic count of 6/10 HPF (1 point) → GAPP score = 3 (intermediate risk) → schedule annual abdominal MRI and yearly plasma‑free metanephrines.
Source: Japan Endocrine Society Clinical Practice Guideline for the Diagnosis and Management of Pheochromocytoma and Paraganglioma 2025, Japan Endocrine Society, 2025, DOI:10.1507/endocrj.EJ25-0165
TODO: consider adding scripts/calc.py for the ppgl-gapp-score-application calculator