‘Rainbow pattern’: a dermoscopic sign of invasive melanoma

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Abstract
Background The “rainbow pattern” was initially described as a highly specific dermoscopic feature of Kaposi’s sarcoma. Since then, it has been reported in many benign and malignant cutaneous tumors, including few melanomas. Aim To determine the frequency and presentation of this dermoscopic pattern in primary cutaneous melanomas in comparison to other cutaneous tumors. Methods The presence of “rainbow pattern” was evaluated in a sample of 1100 dermoscopic images of different melanocytic and non-melanocytic cutaneous neoplasms. Results Rainbow pattern was observed in 23/245 (9.4%) melanomas and 44/855 (5.1%) non-melanoma neoplasms. Melanomas presenting this feature were thicker than 1 mm (82.6%) and 2 mm (43.0%). Compared to non-melanomas, rainbow pattern was more commonly focal (82.7% vs 36.4%, p=0.001) and associated with more than two dermoscopic structures associated to melanoma (100% vs 9%, p=0.001) Conclusion The “rainbow pattern” is a dermoscopic sign that can occasionally be observed in invasive melanomas. In melanomas, this feature is usually associated to other dermoscopic criteria of melanoma and located in a focal and eccentric area, as opposed to a diffuse and isolated presentation in non-melanoma neoplasms.

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