Aim Blue nevus (BN) is a benign melanocytic proliferation that is typically cutaneous. Extracutaneous BN is infrequent and is reported in the mucosa of various organs. Gastrointestinal (GI) tract BN is rare. Here, we describe the clinicopathological findings of the largest series of GI tract BNs.

Methods A search of our Pathology Data System (1984–2019) identified six GI tract blue nevi. Clinical information, pathology reports and available H&E-stained section slides were reviewed.

Results Lesions predominated in the middle-aged adults (mean 54, range 27–80) with a slight female predominance (66%). Most cases arose in the rectum and colon (83%), with one gastric lesion (17%). Four cases were identified during endoscopic examination performed either for screening or for unrelated symptoms (66%). Two patients presented with rectal bleeding (33%) unassociated with the BN. Endoscopically, most lesions appeared as superficial hyperpigmented areas (83%). One case was described as abnormal mucosa (17%). Microscopically, the mucosa was involved in all of the cases (100%). One case showed submucosal extension in addition to the mucosal component (17%). Lesions showed a proliferation of bland spindle cells with abundant granular pigment. No nuclear atypia or mitoses were identified. Immunostains showed immunoreactivity for melanocytic markers. Follow-up information available for five patients showed no recurrences to date (mean follow-up 1 year).

Conclusions BN is a benign melanocytic proliferation. It is important to be aware of the occurrence of such lesions outside of the skin and consider the possibility of BN when pigmented lesions are encountered in the GI tract.