A 52-year-old man from Mumbai presents with a pigmented lesion on his back that was excised. Histopathology shows a melanoma with a Breslow thickness of 2.8 mm, 3 mitoses per mm², and no ulceration. Regarding the AJCC TNM staging of this melanoma, all of the following statements are TRUE EXCEPT:

Question

Accepted Answer

B. A mitotic rate of 3 per mm² automatically upgrades the T stage by one level regardless of thickness. ## AJCC TNM Staging of Cutaneous Melanoma (8th Edition)

### T Stage Classification Rules

**Key Point:** AJCC 8th edition uses Breslow thickness and mitotic rate (or ulceration) as the primary determinants of T stage. The relationship between these factors is hierarchical, not additive.

### Breslow Thickness Tiers

| Thickness | T Stage (without ulceration) | T Stage (with ulceration) |
|-----------|------------------------------|---------------------------|
| ≤ 1.0 mm | T1a (if no mitoses) | T1b (if ≥1 mitosis/mm²) |
| 1.01–2.0 mm | T2a | T2b |
| 2.01–4.0 mm | T3a | T3b |
| > 4.0 mm | T4a | T4b |

### Mitotic Rate Modifiers

**High-Yield:** Mitotic rate (≥1 mitosis/mm²) is used to **upgrade T1 tumors only**:
- T1a (≤1.0 mm, no mitoses) → T1b if ≥1 mitosis/mm²
- For T2 and above, mitotic rate does NOT independently upgrade the stage; thickness is the primary driver.

### Analysis of This Case

- **Breslow thickness:** 2.8 mm → falls in T3 range (2.01–4.0 mm)
- **Mitotic rate:** 3 per mm² → present, but does NOT upgrade T3 further
- **Ulceration:** Absent → T3a (not T3b)

**Therefore, this tumor is T3a.**

### Why Each Option Is Evaluated

1. **"T3b based on thickness and mitotic rate"** — INCORRECT. The tumor is T3a (no ulceration). Mitotic rate alone does not upgrade T3.
2. **"Ulceration is absent, so no upstaging"** — CORRECT. Absence of ulceration keeps it T3a, not T3b.
3. **"Mitotic rate of 3 per mm² automatically upgrades T stage by one level"** — **INCORRECT (THE ANSWER)**. Mitotic rate upgrades only T1 tumors; it does not upgrade T2, T3, or T4 stages.
4. **"Ulceration would have changed T3a to T3b"** — CORRECT. If ulceration were present, this would be T3b.

**Clinical Pearl:** A common exam trap is assuming mitotic rate is a universal T-stage modifier. In reality, it is only used to upgrade T1 melanomas. For thicker tumors, Breslow thickness and ulceration are the determinants.

**Mnemonic:** **MITOSIS MODIFIES T1 ONLY** — Mitotic rate is a T1 upgrader; thickness and ulceration drive T2–T4.

Answer

A. Ulceration is absent, so the tumor does not qualify for upstaging due to this adverse feature

Answer

C. The primary tumor is classified as T3b based on thickness and mitotic rate

Answer

D. The presence of ulceration would have changed the T3a classification to T3b

A 52-year-old man from Mumbai presents with a pigmented lesion on his back that was excised. Histopathology shows a melanoma with a Breslow thickness of 2.8 mm, 3 mitoses per mm², and no ulceration. Regarding the AJCC TNM staging of this melanoma, all of the following statements are TRUE EXCEPT:

Explanation

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