Benign or aggressive? Understanding spinal melanocytomas in comparison to malignant melanoma

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INTRODUCTION: Spinal melanocytic tumors are rare, with limited data on their clinical course and aggressiveness. Since intraoperative dark pigmentation and infiltrative margins can lead to misclassification of MC as MM-especially in the absence of a known primary-this multicenter study characterizes melanocytomas (MC) and contrasts them with malignant melanoma (MM). METHODS: We retrospectively analyzed 56 patients with spinal intradural melanocytic tumors (2010-2024) from seven European neurosurgical centers. Clinical, radiological, histological, and surgical features were analyzed. Univariate and multivariate analyses were performed to identify prognostic risk factors. RESULTS: The study included 22 patients with spinal MC and 34 patients with MM. Median age was comparable (61 vs. 58 years, p = 0.09), but MC patients had a longer symptom history (13 vs. 1.3 months, p = 0.0001) and more often intramedullary tumors (72.7% vs. 2.9%, p < 0.0001). Gross total resection was achieved in 40.9% of MC cases and 61.8% of MM cases (p = 0.07), with instrumentation required more often for MM (p = 0.0022). Ki-67 proliferation index was significantly higher in MM than MC (26.7% vs. 6.6%, p < 0.0001). Postoperative deficits were more frequent in MC (54.6% vs. 14.7%, p = 0.002) and MCs showed higher frequency of ataxia postoperatively (36.4% vs. 11.8%, p = 0.04). MM patients received more adjuvant therapy (88.2% vs. 31.8%, p = 0.0001), with a trend toward higher local recurrence (26.5% vs. 14.7%, p = 0.31). CONCLUSION: Our study demonstrates that MC, though considered benign, carries a high risk of postoperative deficits. Furthermore, GTR was achieved in only 40% of cases, underscoring its locally infiltrative nature and potential for semi-benign biology.

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