Development and Validation of a Modified Pathologic Nodal Classification System for Cutaneous Melanoma

Given the evolving patterns of lymph node evaluation for cutaneous melanoma, it is unclear whether the current nodal classification system will continue to accurately reflect prognosis in the modern era. Existing nodal staging for cutaneous melanoma was developed primarily for patients undergoing completion lymph node dissection (CLND) for node-positive disease and does not produce groups with continuously increasing mortality.

To develop and validate a modified nodal classification system for cutaneous melanoma.

This retrospective cohort analysis included 105 785 patients with cutaneous melanoma undergoing surgery and nodal evaluation from January 1, 2004, to December 31, 2015, in the National Cancer Database. Extent of lymph node dissection was available for patients diagnosed in 2012 and onward. Multivariable models were generated with number of positive lymph nodes modeled using restricted cubic splines. A modified nodal classification system was derived using recursive partitioning analysis (RPA). The proposed lymph node classification system was validated in 85 499 patients from the Surveillance, Epidemiology, and End Results (SEER-18) database. Data were analyzed from April 9, 2020, to May 28, 2021.

Overall survival.

Among the 105 785 patients included in the analysis (62 496 men [59.1%]; mean [SD] age, 59.9 [15.5] years), number of positive lymph nodes (hazard ratio [HR] per lymph node for 0 to 2 positive lymph nodes, 2.48 [95% CI, 2.37-2-61; P < .001]; HR per lymph node for ≥3 positive lymph nodes, 1.10 [95% CI 1.07-1.13; P < .001]), clinically detected metastases (HR, 1.35; 95% CI, 1.27-1.42; P < .001), and in-transit metastases (HR, 1.48; 95% CI, 1.34-1.65; P < .001) were independently associated with mortality. An RPA-derived system using these variables demonstrated continuously increasing mortality for each proposed lymph node classification group, with HRs of 1.83 (95% CI, 1.76-1.91) for N1a, 2.72 (95% CI, 2.58-2.86) for N1b, 3.79 (95% CI, 3.51-4.08) for N2a, 4.56 (95% CI, 4.22-4.92) for N2b, 6.15 (95% CI, 5.59-6.76) for N3a, and 8.25 (95% CI, 7.64-8.91) for N3b in the proposed system (P < .001). By contrast, the current American Joint Committee on Cancer (AJCC) nodal classification system produced a more haphazard mortality profile, with HRs of 1.83 (95% CI, 1.76-1.91) for N1a, 3.81 (95% CI, 3.53-4.12) for N1b, 2.59 (95% CI, 2.30-2.93) for N1c, 2.71 (95% CI, 2.56-2.87) for N2a, 4.51 (95% CI, 4.17-4.87) for N2b, 3.44 (95% CI, 2.60-4.55) for N2c, 6.06 (95% CI, 5.51-6.67) for N3a, 8.15 (95% CI, 7.54-8.81) for N3b, and 6.90 (95% CI, 5.60-8.49) for N3c. As a sensitivity analysis, the proposed system continued to accurately stratify patients when excluding those undergoing CLND for microscopic lymph node metastases. This system was validated for overall survival and cause-specific mortality in SEER-18. Last, a new overall staging system for node-positive patients was developed by RPA and demonstrated improved concordance vs the AJCC, 8th edition system (C statistic, 0.690 [95% CI, 0.689-0.691] vs 0.666 [95% CI, 0.666-0.668]).

The findings of this cohort study suggest that a modified nodal classification system can accurately stratify mortality risk in cutaneous melanoma in an era of increasing use of sentinel lymph node biopsy without CLND and should be considered for future staging systems.