A 58-year-old Indian woman undergoes mastectomy for a 2.5 cm invasive ductal carcinoma of the breast. Histopathology shows moderate nuclear pleomorphism, 18 mitotic figures per 10 high-power fields, and moderate tubule formation. Immunohistochemistry is positive for ER and PR, and HER2 is negative. Sentinel lymph node biopsy shows metastases in 3 out of 4 sampled nodes. What is the Nottingham Prognostic Index (NPI) score, and what is the predicted 10-year survival?

Explanation

## Nottingham Prognostic Index (NPI) Calculation **Key Point:** The NPI is a validated prognostic tool for breast cancer that combines tumor size, histological grade, and lymph node status. It is superior to TNM staging alone for predicting long-term outcome. ### NPI Formula $$\text{NPI} = (0.2 \times \text{Tumor size in cm}) + \text{Histological Grade} + \text{Lymph Node Score}$$ ### Step-by-Step Calculation #### 1. Tumor Size Component - Tumor size = 2.5 cm - Contribution = 0.2 × 2.5 = **0.5** #### 2. Histological Grade (Bloom-Richardson-Elston / Nottingham Grading System) Histological grade is determined by three components: - **Tubule formation** (moderate = 2 points) - **Nuclear pleomorphism** (moderate = 2 points) - **Mitotic count** (18 per 10 HPF = 3 points, since >11 mitoses/10 HPF = score 3) - **Total score = 2 + 2 + 3 = 7 → Grade 3 (poorly differentiated)** - NPI contribution = **3** #### 3. Lymph Node Status - 3 out of 4 sentinel nodes involved = **1–3 positive nodes** - Standard NPI lymph node score: **1** = node negative; **2** = 1–3 positive nodes; **3** = ≥4 positive nodes or internal mammary involvement - With 3 positive nodes → Lymph node score = **2** #### 4. NPI Score $$\text{NPI} = 0.5 + 3 + 2 = \mathbf{5.4}$$ ### NPI Prognostic Groups & 10-Year Survival | NPI Score | Prognostic Group | 10-Year Survival | Risk Category | |-----------|------------------|------------------|---------------| | ≤2.4 | Good | ~90% | Low | | 2.4–3.4 | Moderate I | ~80% | Intermediate | | 3.4–5.4 | Moderate II | ~70% | Intermediate | | 5.4–7.4 | Poor | ~50% | High | | >7.4 | Very Poor | <30% | Very High | **High-Yield:** An NPI of **5.4** places this patient at the boundary of the **Moderate II** prognostic group (3.4–5.4), with a predicted 10-year survival of approximately **70%**. This patient also benefits from adjuvant endocrine therapy given ER/PR positivity. **Clinical Pearl:** The lymph node score in the NPI uses a 3-tier system: score 1 (node-negative), score 2 (1–3 positive nodes), score 3 (≥4 positive nodes). This patient has 3 positive nodes, which correctly maps to a score of 2 — not 3. Misassigning the lymph node score is the most common calculation error in NPI questions. *(Reference: Galea MH et al., Breast Cancer Research and Treatment, 1992; also cited in Robbins & Cotran Pathologic Basis of Disease, 10th ed.)* **Mnemonic:** **"Size × 0.2 + Grade + Node Score = NPI"** — Node score: 1 = negative, 2 = 1–3 nodes, 3 = ≥4 nodes.