GASTROINTESTINAL HEMORRHAGE (2): Melena. Melena, the passage of black, tarry stools, usually implies blood loss greater than 500 ml originating anywhere between the oropharynx and the right hemicolon. Melena occurs most often, Melanocyte differentiation and mechanosensation are differentially modulated by distinct extracellular matrix proteins EMBO Reports Springer Nature Link Differentiating between early melanomas and melanocytic nevi: A state of the art review ScienceDirect From melanocytes to melanomas Nature Reviews Cancer Oral Melanotic Macule: Symptoms and Treatment Skinsight