Risk of Regional Node Metastasis in 0.70 mm Thick Melanoma
The risk of regional node metastasis in a 0.70 mm thick melanoma is less than 5%.
Evidence-Based Assessment
According to the American Society of Clinical Oncology (ASCO) and Society of Surgical Oncology (SSO) clinical practice guideline, melanomas with Breslow thickness ≥0.75 mm have a sentinel lymph node (SLN) positivity likelihood of 8.8% (95% CI, 6.4% to 11.2%) 1. Since the melanoma in question is 0.70 mm thick, which falls below this threshold, the risk would be even lower.
The National Comprehensive Cancer Network (NCCN) guidelines specifically address this issue, stating that "in general, SLNB is not recommended for primary melanomas ≤0.75 mm thick, unless there is significant uncertainty about the adequacy of microstaging" 1. This recommendation is based on the low probability of finding positive sentinel nodes in such thin melanomas.
Risk Stratification for Thin Melanomas
For melanomas ≤0.75 mm thick, the risk factors that might increase the likelihood of sentinel node positivity include:
- Ulceration
- High mitotic rate
- Lymphovascular invasion
- Clark level ≥ IV
However, the NCCN guidelines note that these conventional risk factors "are very uncommon in melanomas ≤0.75 mm thick" 1. When these factors are absent in a 0.70 mm melanoma, the risk of regional node metastasis remains well below 5%.
Clinical Decision-Making
The 2018 ASCO/SSO guidelines report that a systematic review of 60 studies found that after adjusting for all potential risk factors, melanomas with Breslow thickness <0.75 mm have a significantly lower risk of SLN positivity compared to those ≥0.75 mm 1.
The NCCN guidelines from 2013 specifically state that "SLNB is not recommended for primary melanomas ≤0.75 mm thick" 1, which has been consistently maintained in later versions of the guidelines 1.
Practical Implications
For a 0.70 mm thick melanoma:
- Sentinel lymph node biopsy is generally not recommended due to the low yield
- The risk of regional node metastasis is less than 5%
- Wide local excision with appropriate margins is the standard treatment
- Regular follow-up is important for monitoring
Common Pitfalls to Avoid
Overestimating risk: Don't assume that all melanomas carry a significant risk of nodal metastasis. Thin melanomas (<0.75 mm) without adverse features have an excellent prognosis.
Unnecessary procedures: Performing SLNB on all patients with thin melanomas leads to unnecessary procedures with potential complications for very little benefit.
Neglecting other risk factors: While thickness is the primary determinant, in rare cases where ulceration or high mitotic rate is present in a thin melanoma, the risk may be slightly higher.
In conclusion, based on the most recent and highest quality evidence, the risk of regional node metastasis in a 0.70 mm thick melanoma is less than 5% (option A).