Validation of previously proposed criteria for selecting nonulcerated T1b melanoma patients for sentinel lymph node biopsy.

BACKGROUND

Controversy exists regarding the overutilization of sentinel lymph node biopsy for nonulcerated T1b melanomas. We previously proposed an algorithm based on mitotic rate, age, and Breslow thickness that suggested that over half of nonulcerated T1b patients could forgo sentinel lymph node biopsy. We sought to validate this model and compare it with the Melanoma Institute Australia's nomogram.

METHODS

The 2022 National Cancer Database Public Use File was used to identify clinically node-negative melanoma patients with nonulcerated T1b melanomas staged by sentinel lymph node biopsy from 2016 to 2022. The sentinel lymph node positivity rates for our previously described low-risk groups (mitotic rate = 0 mm2 or mitotic rate ≥1/mm2 + thickness <1.0 + age >56) were calculated. The Melanoma Institute Australia's nomogram was used to calculate predicted sentinel lymph node positivity for patients with pathologically complete records.

RESULTS

We identified 18,957 patients with nonulcerated T1b melanomas who underwent sentinel lymph node biopsy. A mitotic rate of <1/mm2 had a low risk of a positive sentinel lymph node (3.9%; 95% confidence interval, 3.5-4.4%). The other previously proposed low-risk group had a sentinel lymph node-positive rate exceeding the >5% threshold (5.7%; 5.0-6.4%). Using a mitotic rate <1/mm2 as a criterion, 38% of T1b nonulcerated patients could avoid sentinel lymph node biopsy. More patients would avoid sentinel lymph node biopsy with our algorithm versus the Melanoma Institute Australia's nomogram (39% vs 28%). For those with mitotic rate = 0, age cutoffs of ≤42 (sentinel lymph node + rate 7.0%, 5.2-9.1%) or ≤56 (sentinel lymph node + rate 5.4%, 4.3-6.6%) identified younger patients for whom sentinel lymph node biopsy should be considered.

CONCLUSION

One-third of patients with nonulcerated T1b melanomas have a low predicted risk of a positive sentinel lymph node. When parameters are not available to calculate the Melanoma Institute Australia's nomogram, mitotic rate in conjunction with age is a suitable decision aid for recommending sentinel lymph node biopsy.