title: Amelanotic malignant melanoma: two collision tumors presenting as basal cell carcinoma and atypical fibroxanthoma.
abstract: Collision (contiguous) tumors of the skin can result in misleading clinicopathological presentations, and the choice of appropriate diagnostic techniques may prevent incomplete diagnosis and management. We report 2 cases of collision tumors involving amelanotic malignant melanoma of the back. One patient is a 79-yr-old male with an 8.7 x 5.5 x 4.5 cm polypoid lesion that on shave biopsy was diagnosed as basal cell carcinoma. Subsequent excision showed that the lesion was largely composed of amelanotic melanoma underlying a relatively small and thin basal cell carcinoma, and this probably would have been demonstrated in a punch (rather than shave) biopsy. The other patient is a 71-yr-old male with a 1 cm exophytic lesion on the back, which was determined microscopically to be melanoma, and a 0.6 cm papule on the back. This lesion was composed of 2 distinct contiguous neoplastic infiltrates, the predominant component being an atypical fibroxanthoma and the smaller component an amelanotic melanoma (primary vs metastatic), with diagnostic confirmation requiring multiple immunohistochemical stains.
authors.affiliation: Pathology & Laboratory Medicine Service, Veterans Affairs Medical Center, and Department of Pathology and Laboratory Medicine, University of Kansas Medical Center, Kansas City, Kansas 64128, USA.
authors.forename: Douglas H
authors.initials: DH
authors.lastname: McGregor
authors.forename: Rachel
authors.initials: R
authors.lastname: Cherian
authors.forename: Maria M
authors.initials: MM
authors.lastname: Romanas
authors.forename: Ozlem
authors.initials: O
authors.lastname: Ulusarac
authors.forename: Sharad C
authors.initials: SC
authors.lastname: Mathur
authors.forename: Mary M
authors.initials: MM
authors.lastname: Feldman
mesh_terms: D000368:Aged; D000951:Antigens, Neoplasm / Q000378:metabolism; D014408:Biomarkers, Tumor / Q000378:metabolism; D002280:Basal Cell Carcinoma / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology; D003937:Diagnosis, Differential; D018219:Histiocytoma, Benign Fibrous / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D018328:Melanoma, Amelanotic / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology; D009378:Neoplasms, Multiple Primary / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology; D012878:Skin Neoplasms / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology
chemical_list: D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor