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Metastatic melanoma without an identifiable primary lesion presents a unique diagnostic challenge and raises consideration of immune-mediated regression or non-cutaneous tumour origin. We describe the case of a man in his 80s diagnosed with metastatic melanoma, for whom a thorough skin examination and staging workup revealed no definitive primary lesion. Dermatologic evaluation revealed vitiligo-like depigmentation and a grey macule with clinical features suggestive of regression. While a definitive primary site could not be established, the constellation of clinical and dermatologic findings raises consideration of melanoma-associated depigmentation, an immune phenomenon in which both melanocytes and melanoma cells are targeted. This case highlights how immune-mediated mechanisms may obscure the detection of a primary lesion. Recognition of this pattern may aid in evaluating atypical presentations and contribute to the broader understanding of immune involvement in melanoma progression.