CRTC1::TRIM11 Cutaneous Tumors With Atypia: Melanoma Mimicry, Aggressive Potential, and Methylation Classifier Limitations.

CRTC1::TRIM11 cutaneous tumors are an emerging subset of MITF pathway-activated neoplasms that typically present as dermal nodules and can closely mimic clear cell sarcoma or malignant melanoma. Most reported tumors behave in an indolent manner, yet rare malignant cases have been documented. We report three additional CRTC1::TRIM11 cutaneous tumors with atypical features, including two patients with nodal or visceral disease at presentation. Histologically, all three tumors showed marked cytologic atypia with prominent nucleoli, and the usual nested and short-fascicular architecture was largely replaced by broad sheet-like growth, raising concern for melanoma. The tumors expressed SOX10 (diffuse) and S100 protein (patchy) with focal to absent expression of Melan-A and HMB45. PRAME was negative. CRTC1::TRIM11 was confirmed in all tumors. Two tumors harbored TERT promoter mutations, and one showed additional low-level copy-number gains of 1q, 8q, and 12q with 14q loss. In one case, methylation profiling yielded a clear cell sarcoma score of 0.885, just below the confidence threshold, likely due to shared CREB-MITF pathway activation and the lack of a dedicated CRTC1::TRIM11 reference class. A literature review identified nine previously reported metastatic CRTC1::TRIM11 cutaneous tumors. When combined with our series, extremities were the predominant primary site, and metastases most often involved regional lymph nodes and the lung. Fusion status remains the molecular gold standard, while secondary events such as TERT promoter mutations and 8q gains may contribute to aggressive behavior in a subset of tumors.