Researchers propose using an externally validated nomogram to better select patients with T1 melanoma to undergo sentinel node biopsy (J Clin Oncol. 2020 Mar 13. Epub ahead of print).

“Thin melanomas (T1; ≤ 1 mm) constitute 70% of newly diagnosed cutaneous melanomas. Regional node metastasis determined by sentinel node biopsy…is an important prognostic factor for T1 melanoma,” explained Andrea Maurichi, MD, Melanoma and Sarcoma Unit, Department of Surgery, Fondazione IRCCS Istituto Nazionale dei Tumori di Milano, Italy, and colleagues.

“However, current melanoma guidelines do not provide clear indications on when to perform [sentinel node biopsy] in T1 disease and stress an individualized approach to [sentinel node biopsy] that considers all clinicopathologic risk factors,” they continued.

Thus, Dr Maurichi et al sought to identify causes of sentinel node status for inclusion in an externally validated nomogram that could help better select patients with T1 disease for sentinel node biopsy.

A total of 3666 patients with T1 disease consecutively treated between 2001 and 2018 at the Istituto Nazionale Tumori were included in the development cohort. An additional 4227 patients with T1 disease treated at 13 other centers across Europe during the same time period formed the validation cohort.

The investigators applied a random forest to the development data set to select characteristics tied to sentinel node status for inclusion in a multiple binary logistic model from which a nomogram was expounded. The clinical effectiveness of the nomogram was evaluated via decision curve analyses.

Overall, 1635 patients in the development cohort underwent sentinel node biopsy, 108 (6.6%) of whom were sentinel node positive. Age, growth phase, Breslow thickness, ulceration, mitotic rate, regression, and lymphovascular invasion were factors significantly tied sentinel node status, according to univariable analysis.

A total of 6 variables (not growth phase) were selected for inclusion in the logistic model and nomogram using the random forest procedure.

“The nomogram proved well calibrated and had good discriminative ability in both cohorts,” Dr Maurichi and co-investigators said, adding that the nomogram showed superior net benefit versus each individual variable included in it as well as with variables suggested by current guidelines, according to decision curve analyses.

“We propose the nomogram as a decision aid in all patients with T1 melanoma being considered for [sentinel node metastasis],” they concluded.—Hina Porcelli