title: Amelanotic melanoma: a detailed morphologic analysis with clinicopathologic correlation of 75 cases.
abstract: Amelanotic melanoma can have a varied appearance both clinically and microscopically. Here, we present our experiences with 75 cases of amelanotic melanoma defined clinically as a non-pigmented lesion and histopathologically as a tumor lacking significant melanization. We evaluated microscopic features such as morphology, mitotic count, nuclear atypia and presence of solar elastosis. Our amelanotic melanomas exhibited the following morphology: epitheloid (72%), spindled (18.7%) or desmoplastic (5.3%). In addition, we obtained patient information and clinical presentations on most of the cases (74/75; 98.7%) and follow-up data on 40% (30/75) of the cases. The majority of amelanotic melanomas in men were found on the trunk (13/45; 29%), head and neck (12/45; 26.7%), and lower limb (13/45; 29%) and in women were found on the lower limb (12/30; 40%), upper limb (10/30; 33.3%) and head and neck (6/30; 20%). In addition, we found that an increase in mitotic index correlated with worse survival (p < 0.026), whereas there were no differences in survival for other pathological features, such as nuclear atypia or solar elastosis. Furthermore, in cases with available tissue, all amelanotic melanoma expressed microphthalmia-associated transcription factor and tyrosinase, suggesting that the tumor cells retained melanocytic lineage and an enzyme in melanin formation, respectively. As the occurrence of amelanotic melanoma and the expression melanoma markers were similar to pigmented melanoma, we favor that amelanotic melanoma represents a subtype of melanoma rather than poorly differentiated or de-differentiated melanoma.
authors: Dermatopathology Division, Department of Pathology and Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
authors: Wang L
authors: WL
authors: Cheung
authors: Rishi R
authors: RR
authors: Patel
authors: Aimee
authors: A
authors: Leonard
authors: Bahar
authors: B
authors: Firoz
authors: Shane A
authors: SA
authors: Meehan
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000096:biosynthesis*; D002467:Cell Nucleus / Q000378:metabolism / Q000473:pathology; D018572:Disease-Free Survival; D005260:Female; D005500:Follow-Up Studies; D015972:Gene Expression Regulation, Neoplastic; D006258:Head and Neck Neoplasms / Q000378:metabolism / Q000401:mortality / Q000473:pathology; D006801:Humans; D008297:Male; D008543:Melanins / Q000378:metabolism; D018328:Melanoma, Amelanotic / Q000378:metabolism / Q000401:mortality / Q000473:pathology; D008875:Middle Aged; D008938:Mitosis; D012189:Retrospective Studies; D012737:Sex Factors; D012878:Skin Neoplasms / Q000378:metabolism / Q000401:mortality / Q000473:pathology; D015996:Survival Rate
chemical_list: D014408:Biomarkers, Tumor; D008543:Melanins