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Objective: The immune system can halt cancer progression by suppressing outgrowth of clinically occult micrometastases in a state of cancer-immune equilibrium. Cutaneous melanoma provides a unique opportunity to study the immune contexture of such lesions, as miniscule skin metastases are accessible to clinical inspection and diagnostic biopsy., Methods: Here, we analysed by multiplex immunofluorescence microscopy samples from a melanoma patient presenting with an overt and an occult in-transit metastasis (ITM), the latter of which appeared as a small erythematous papule., Results: Microarchitecture and immune composition in the two lesions were vastly different. CD4 + and CD8 + T cells accumulated around the margin of the overt SOX10 + Melan A + ITM but were largely excluded from the tumor centre. By contrast, the occult micrometastasis contained only few SOX10 + Melan A - melanoma cells which were scattered within a dense infiltrate of T cells, including a prominent population of CD103 + CD8 + T cells resembling tissue-resident memory T (T RM ) cells. Notably, almost every single melanoma cell in the micrometastasis was in close proximity to these T RM -like cells., Conclusion: Such results support the emerging concept that CD103 + CD8 + T RM cells are key mediators of cancer surveillance and imply an important function of these cells in controlling clinically occult micrometastases in humans., Competing Interests: The authors declare no conflict of interest., (© 2019 The Authors. Clinical & Translational Immunology published by John Wiley & Sons Australia, Ltd on behalf of Australian and New Zealand Society for Immunology Inc.)