A 58-year-old woman from Mumbai presents with a 10-month history of a changing pigmented lesion on her right calf. Examination reveals an irregularly bordered, asymmetrical nodule measuring 12 mm with mixed colours (dark brown, black, and red). The lesion is firm and slightly raised. Dermoscopy shows atypical vascular patterns and irregular dots. Excisional biopsy confirms melanoma with Breslow thickness of 3.5 mm, ulceration present, and mitotic rate of 8/mm². Sentinel lymph node biopsy shows micrometastasis in one lymph node (tumour burden <0.1 mm). No distant metastases are detected. What is the AJCC TNM stage?

Explanation

## AJCC TNM Staging for Cutaneous Melanoma with Nodal Micrometastasis **Key Point:** According to the AJCC 8th Edition, T3b (Breslow 3.5 mm with ulceration) combined with N1a (micrometastasis in 1 lymph node) and M0 corresponds to **Stage IIIC**, not Stage IIIB. ### T-Stage Determination - **Breslow thickness:** 3.5 mm → falls in the 2.01–4.0 mm range - **Ulceration:** Present - **T-Stage:** **T3b** (2.01–4.0 mm with ulceration) ### N-Stage Determination | Nodal Involvement | Tumour Burden | N-Stage | |---|---|---| | 1 node (clinically occult/micro) | Any | N1a | | 1 node (clinically detected/macro) | Any | N1b | | 2–3 nodes (clinically occult) | Any | N2a | | 2–3 nodes (≥1 clinically detected) | Any | N2b | | 4+ nodes, matted, or in-transit + nodes | Any | N3 | - **Nodal status:** Micrometastasis in one lymph node (sentinel node biopsy) = **N1a** - **M-Stage:** M0 (no distant metastases) ### Stage Grouping (AJCC 8th Edition) | T-Stage | N-Stage | M-Stage | Clinical Stage | |---|---|---|---| | T1a–T2a | N1a–N2a | M0 | IIIA | | T1b–T2b | N1a–N2b | M0 | IIIB | | T2a | N1b–N2b | M0 | IIIB | | **T3b** | **N1a** | **M0** | **IIIC** | | T3b–T4b | N1b–N3 | M0 | IIIC | | T4b | N1a–N2a | M0 | IIIC | **The critical distinction:** Stage IIIB requires a non-ulcerated primary (e.g., T3a N1a M0). Once ulceration is present (T3b), even a single micrometastatic node (N1a) pushes the stage to **IIIC**. **High-Yield:** In AJCC 8th Edition melanoma staging, ulceration is a powerful upstaging factor. T3b N1a M0 = Stage IIIC (5-year survival ~40%). This mandates adjuvant systemic therapy (PD-1 inhibitors such as pembrolizumab/nivolumab, or BRAF/MEK inhibitors if BRAF V600-mutant). **Clinical Pearl:** Sentinel lymph node biopsy is the gold standard for detecting occult nodal disease in melanomas >1 mm Breslow thickness. Even microscopic nodal involvement significantly worsens prognosis and stage. The presence of ulceration in the primary tumour is an independent adverse prognostic factor that upgrades stage grouping. **Mnemonic:** **Ulceration + any nodal disease ≥ T3b → at least Stage IIIC** in AJCC 8th Edition. [cite: AJCC Cancer Staging Manual, 8th Edition — Cutaneous Melanoma Chapter; Gershenwald JE et al., CA Cancer J Clin 2017]