A 58-year-old man presents with a 2-cm dark brown lesion on his left shin that has been present for 8 years without significant change. On dermoscopy, there is a reticular (net-like) pattern with brown globules and no ulceration. Histopathology shows melanoma with a Breslow thickness of 1.2 mm, Clark level III, and mitotic rate of 2/mm². There is no evidence of ulceration or regression. What is the most important prognostic factor that will influence his 5-year survival in this case?

Explanation

## Prognostic Factors in Melanoma **Key Point:** Breslow thickness (vertical depth of invasion in millimeters) is the single most important prognostic factor for cutaneous melanoma and is the primary determinant of staging and survival prediction. ### Breslow Thickness Classification | Thickness | Stage | 5-Year Survival | Risk Category | |-----------|-------|-----------------|----------------| | ≤0.8 mm | IA | 95–99% | Low | | 0.8–1.0 mm | IB | 90–95% | Intermediate | | 1.01–2.0 mm | IB–IIA | 80–90% | Intermediate | | 2.01–4.0 mm | IIB–IIC | 60–75% | High | | >4.0 mm | III–IV | <60% | Very high | **High-Yield:** In this patient, Breslow thickness of 1.2 mm places him in the intermediate-risk category (Stage IB–IIA) with approximately 80–90% 5-year survival. This single measurement is more predictive than Clark level, mitotic rate, or presence/absence of ulceration. ### Why Breslow Thickness Dominates 1. **Direct correlation with lymph node involvement** — thicker lesions have higher rates of occult nodal metastases 2. **Incorporated into AJCC staging** — the primary determinant of T-stage (T1–T4) 3. **Validated across multiple cohorts** — strongest independent prognostic variable in multivariate analysis ### Other Prognostic Factors (Secondary) - **Ulceration** — presence worsens prognosis by ~1 stage; absence is favorable but not the primary driver - **Mitotic rate** — relevant for thin melanomas (≤1 mm) to distinguish T1a from T1b; less predictive in thicker lesions - **Clark level** — largely replaced by Breslow thickness in modern staging; less reproducible and less prognostically powerful - **Regression** — presence may indicate immune response; significance debated **Clinical Pearl:** A patient with Breslow 1.2 mm, no ulceration, and low mitotic rate (2/mm²) is actually lower-risk within the intermediate category and may not require sentinel lymph node biopsy (SLNB) depending on institutional guidelines, though SLNB is often offered for T1b–T2 lesions. **Mnemonic — ABCDE of Melanoma Prognosis:** **A**symptry, **B**reslow thickness, **C**lark level, **D**ermal mitotic rate, **E**xcision margins — but Breslow is the kingpin. [cite:Robbins 10e Ch 25]