Miscoding of Melanoma Thickness in SEER: Research and Clinical Implications.

Melanoma-related deaths and metastases among patients with thin (≤1 mm) and ultrathin (≤0.25 mm) melanomas have been reported. These observations might reflect adverse biology and/or errors in administrative data. Cumulative melanoma-related death rates for thickness groups of patients with thin melanomas were compared among five cohorts including the Surveillance, Epidemiology, and End Results (SEER) registry. Thickness in one SEER region was reexamined in pathology reports. The 5-year cumulative melanoma-related death rate of patients with ultrathin melanomas was higher in SEER (2.8%) compared with other registries (0.6-0.9%). The rates across the 16 SEER regions were 0.25% to 8.4%. In SEER, 21% of thin melanomas were ultrathin; in other registries, they comprised 5.8-15%. A reexamination of thickness in one SEER site revealed that 114 of 447 ultrathin melanomas had errors; after correction, only 17 of the 114 remained ultrathin. The majority of errors were related to decimal point placement. The 86 thin melanomas reclassified to >1.00 mm included 96% of the original ultrathin-associated deaths and 100% of the original positive lymph nodes. Significant miscoding of thickness that is concentrated in ultrathin lesions is present in SEER and results in mischaracterization of patient outcomes. When using administrative data, validation of results can identify critical data issues.