**6. Diagnosis and staging**

As CM and MM are known for early hematogenous spread, secondary gastrointestinal melanomas are not rare. Hence, for differentiation between primary and secondary melanoma, the following criteria must be satisfied: absence of melanoma at any other cutaneous or mucosal sites confirmed by thorough clinical including genital, oropharyngeal, ophthalmological and endoscopic examination; no past history of melanoma and presence of atypical melanocytes in the basal epithelium of the tissue sample [36].

There is no formal staging system for AM. However, the most commonly described system for AM in previous studies is the Ballantye clinical system which has three stages as follows: Stage I – localized disease, Stage II – presence of inguinal or pelvic lymph nodes and stage III – distant metastasis [37–39]. Interestingly, a recent study by Nagarajan et al. involving 160 AM patients found that the clinical American Joint Cancer Committee (AJCC) staging system (8th edition) for CM significantly stratified disease-specific survival of AM patients. Moreover, the authors recommended slight modifications in the AJCC 'T' category criteria of staging for better stratification [40]. Hence, either of the two staging systems can be used to prognosticate the disease in patients with AM.
