The majority of melanocytic lesions can be diagnosed clinically, dermoscopically and by histology. Yet, dermato-pathologists and clinicians may face tumours that cannot be classified as bona fide benign or malignant. The World Health Organization Classification of Skin Tumours recognized this dilemma and included the term MelTUMP and melanocytoma to account for melanocytic tumours with ambiguous morphology, architecture, and cytology.1 Similar to challenges with their clinical and histologic classification, it is hard to predict the biological behaviour of MelTUMPs at the time of diagnosis. For the most part, however, they rarely cause distant metastasis and death. Nonetheless, lymph node involvement is not uncommon. This may sound like a contradiction, but actually reflects the same dilemma present in diagnosing such tumours: they are neither unequivocally good nor bad. Many terms have been introduced to reflect this grey zone in terms of diagnosis and course of the disease: MelTUMP (melanocytic tumour of uncertain malignant potential), PEM (pigmented epithelioid melanocytoma), ATM (animal type melanoma), AST (atypical Spitz tumour), and many others, all trying to tackle characteristic features for diagnosis. While it may be possible to histologically find some commonality to define subgroups within the collection of MelTUMPs, interrater agreement between dermatopathologists is typically poor. However, all terms have one thing in common: they communicate uncertainty. This also affects clinical decisions and raises several questions how to manage such lesions: Which excision margins are advisable? Should sentinel lymph node (SLN) surgery be performed? Is adjuvant systemic treatment warranted? A recently published systematic review by Varey et al.2 aimed to address some of these questions. Key messages from this article are: 5â10 mm excision margins for the primary tumour appear to be an appropriate balance between surgery-associated morbidity and adequacy of treatment for MelTUMPs. Tumour cell deposits in the SLN are frequent (even compared to clear-cut cutaneous melanomas), and even more frequent in younger patients (>50% positivity rate in patients <18 years of age). However, of the 288 patients analysed in the above study with positive SLN, only 15 developed further disease, of which three died. Thus, the prognostic value of the SLNB is poor. Altogether this paper provides a useful guidance for managing MelTUMPs and has one core message: first do no harm. We are looking forward to seeing data solving the molecular puzzle of MelTUMPs in the future, which has the potential to shed light into this grey zone of melanocyte biology. Open Access funding enabled and organized by Projekt DEAL. CP has received honoraria and travel support from BMS, MSD, Roche, Almirall, Pelpharma, Sanofi, Pfizer, Merck, Abbvie, and Novartis all unrelated to this manuscript.