A 58-year-old Indian woman presents with a 4-month history of a dark nodular lesion on her right calf. On examination, she has a 12 mm dark brown-black nodule with irregular borders and surface bleeding. Histopathology reveals invasive melanoma with Breslow thickness of 3.8 mm, ulceration present, 8 mitoses per mm², and Clark level IV invasion. Sentinel lymph node biopsy shows 1 micrometastasis (0.5 mm) in a single right inguinal lymph node with no extranodal extension. No distant metastases are detected on staging imaging. What is the AJCC TNM stage?

Explanation

## AJCC TNM Staging of Melanoma with Nodal Micrometastasis ### Clinical Data Summary - **Breslow thickness:** 3.8 mm (T3 range) - **Ulceration:** Present → T3b (not T3a) - **Mitotic rate:** 8 per mm² (high, but does not change T-stage given ulceration) - **Sentinel lymph node:** 1 micrometastasis (0.5 mm) in single node = N1a - **No extranodal extension:** Confirms N1a (not N2a or N3) - **Distant metastases:** M0 ### T-Stage: T3b **Key Point:** Breslow thickness 2.01–4.0 mm **with ulceration** = T3b. The presence of ulceration is the critical modifier that escalates from T3a to T3b. ### N-Stage: N1a | Nodal Involvement | Definition | N-Stage | |---|---|---| | 1 lymph node with micrometastasis (<0.1 mm) | Clinically occult | N1a | | 1 lymph node with macrometastasis (≥0.1 mm) | Clinically occult | N1b | | 1 lymph node, any size | Clinically detected | N1c | | 2–3 nodes with micrometastases | Clinically occult | N2a | | 2–3 nodes, 1+ macrometastasis | Clinically occult | N2b | | 2–3 nodes, clinically detected | Any size | N2c | | ≥4 nodes OR in-transit/satellite metastases | Any | N3 | **This patient: 1 micrometastasis (0.5 mm) in 1 node = N1a** ### Stage Determination - **T3b, N1a, M0 = Stage IIIC** **High-Yield:** The AJCC 8th edition uses a **three-tier nodal staging system** based on: 1. **Number of involved nodes** (1 vs. 2–3 vs. ≥4) 2. **Size of metastasis** (micrometastasis <0.1 mm vs. macrometastasis ≥0.1 mm) 3. **Clinical detectability** (clinically occult vs. clinically detected) Micrometastases detected only on sentinel lymph node biopsy are classified as "clinically occult" and assigned the "a" suffix (N1a, N2a). ### Stage Grouping for T3b with Nodal Disease | N-Stage | Stage | |---|---| | N1a | IIIC | | N1b | IIIC | | N1c | IIIC | | N2a | IIIC | | N2b | IIIC | | N2c | IIIC | | N3 | IIIC | **Key Point:** Any T3b or T4 lesion with nodal involvement (N1–N3) is classified as **Stage IIIC**, regardless of the specific N-stage. This reflects the poor prognosis of thick, ulcerated melanomas with lymph node metastases. **Clinical Pearl:** Micrometastases detected on SLNB (N1a, N2a) have a better prognosis than macrometastases (N1b, N2b) or clinically detected nodes (N1c, N2c, N3), but all are still Stage IIIC when combined with T3b or T4 primary tumors. **Mnemonic: SLNB Indications** — **S**ensitivity >90%, **L**ow **M**orbidity, indicated for **B**reslow ≥1 mm, ulceration, high mitotic rate, or young age with intermediate thickness.