A 68-year-old woman from Delhi presents with a 10-month history of a dark nodular lesion on her right calf. She reports recent bleeding and crusting. On examination, the lesion is 12 mm in diameter, dark brown-black, with a firm nodular consistency and surface ulceration. Histopathology shows invasive melanoma with Breslow thickness of 4.2 mm, ulceration present, 8 mitoses per mm², and Clark level IV invasion. Sentinel lymph node biopsy shows micrometastases in 1 of 2 right inguinal lymph nodes (tumor burden <0.1 mm). No distant metastases are detected on staging imaging. According to AJCC 8th edition, what is the stage of this melanoma?

Explanation

## AJCC 8th Edition Staging with Nodal Micrometastases **Key Point:** AJCC 8th edition stratifies nodal disease by number of involved nodes and tumor burden (macrometastases vs. micrometastases). The T-stage is determined solely by Breslow thickness and ulceration status; Breslow 4.2 mm = T4 (>4.0 mm), and with ulceration = **T4b**. ### Prognostic Factors in This Case | Factor | Finding | Stage Impact | |--------|---------|---------------| | **Breslow thickness** | 4.2 mm | T4 (>4.0 mm) | | **Ulceration** | Present | T4b | | **Mitotic rate** | 8/mm² | High risk (does not change T in AJCC 8e) | | **Sentinel lymph node** | 1 node with micrometastases (<0.1 mm) | N1a | | **Distant metastasis** | None | M0 | ### N-Stage Classification (AJCC 8e) | N Stage | Definition | |---------|------------| | **N0** | No regional lymph node metastases | | **N1a** | 1 clinically occult node (detected by SLNB) | | **N1b** | 1 clinically detected node (macrometastasis) | | **N2a** | 2–3 clinically occult nodes | | **N2b** | 2–3 nodes, at least 1 clinically detected | | **N3** | ≥4 nodes, matted nodes, or in-transit/satellite/microsatellite metastases with nodal involvement | ### Stage Assignment (AJCC 8e Table) 1. **T stage:** Breslow 4.2 mm + ulceration = **T4b** 2. **N stage:** 1 node with micrometastases (clinically occult, SLNB-detected) = **N1a** 3. **M stage:** No distant metastases = **M0** 4. **Stage determination:** T4b + N1a + M0 = **Stage IIIC** ### Why Stage IIIC and NOT IIIB? According to the AJCC 8th Edition Melanoma Staging Table (Table 47.3, Gershenwald et al. 2017): | T | N | M | Stage | |---|---|---|-------| | T1a–T2a | N1a–N2a | M0 | IIIA | | T2b–T3b | N1a–N2b | M0 | IIIB | | **T4b** | **N1a** | **M0** | **IIIC** | | Any T | N3 | M0 | IIIC/IIID | - **T4b (Breslow >4 mm + ulceration)** combined with **N1a** maps to **Stage IIIC**, not IIIB. - Stage IIIB requires T2b–T3b (Breslow 1.01–4.0 mm with ulceration, or 2.01–4.0 mm without ulceration) with N1a–N2b. - The original explanation incorrectly assigned T4b as mapping to Stage IIIB with N1a; the correct mapping per AJCC 8e is Stage IIIC. **High-Yield:** The key distinction: T4b (>4 mm + ulceration) with ANY nodal micrometastasis (N1a) = Stage IIIC. Stage IIIB is reserved for lower T-categories (T2b–T3b) with limited nodal involvement. **Clinical Pearl:** Sentinel lymph node biopsy is the gold standard for detecting occult nodal metastases. Even micrometastases (<0.1 mm) detected on SLNB define Stage III disease and significantly impact prognosis and adjuvant therapy decisions. **Mnemonic: T-Stage in Melanoma (AJCC 8e)** - T1: ≤1.0 mm (T1a ≤0.8 mm no ulceration; T1b ≤0.8 mm + ulceration OR 0.8–1.0 mm) - T2: 1.01–2.0 mm - T3: 2.01–4.0 mm - T4: >4.0 mm (Ulceration upgrades "a" to "b" within the same T category) **Warning:** Do not confuse Clark level (histologic depth: I–V) with Breslow thickness (actual measurement in mm). Breslow thickness is the primary prognostic factor in AJCC 8e; Clark level is no longer used for staging. [cite: AJCC Cancer Staging Manual 8th Edition; Gershenwald JE et al. CA Cancer J Clin. 2017;67(6):472–492]