title: Complete regression of primary cutaneous malignant melanoma associated with distant lymph node metastasis: a teaching case mimicking blue nevus.
abstract: BACKGROUND
  Malignant melanoma (MM) tends to be spontaneously regressed, however, complete regression of primary cutaneous MM is an extremely rare phenomenon. Our aim is to be aware that pathologists and/or dermatologists can readily misinterpret it as the other benign or malignant lesions.
  
  
  METHODS
  A gradually growing and verrucous hypopigmented macule had been noticed in the right sole of a 65-year-old Japanese male since 2 years before, and it turned to be a solitary bluish to black patch with surrounding depigmentation and was recently decreased in size. In parallel, the patient had a rapidly growing black-pigmented mass lesion at the right inguen. The cutaneous specimen from the sole showed an aggregation of many melanophages predominantly in the middle to deep layer of dermis, associated with surrounding fibrosis, reactive vascular proliferation and CD8-positive T-lymphocytic infiltrate, covered by attenuated epidermis with absence of rete ridge. However, no remnant MM cells were completely seen in the step-serial sections. We first interpreted it as blue nevus. By contrast, the inguinal mass revealed a diffuse proliferation of highly atypical mono- to multi-nucleated large cells having abundant eosinophilic cytoplasm in the enlarged lymph node tissue. Immunohistochemical findings demonstrated that these atypical cells were specifically positive for HMB45 and Melan A. Therefore, we finally made a diagnosis of complete regression of primary cutaneous MM associated with distant lymph node metastasis of MM.
  
  
  CONCLUSIONS
  Careful, not only general/cutaneous but histopathological, examinations should be necessary and adjunctive aids for reaching the correct diagnosis of complete regression of cutaneous MM.
authors.affiliation: Department of Pathology, Field of Oncology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan. sohsuke@m.kufm.kagoshima-u.ac.jp.|Department of Pathology and Cell Biology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan. sohsuke@m.kufm.kagoshima-u.ac.jp.
authors.forename: Sohsuke
authors.identifier: http://orcid.org/0000-0003-2662-0024
authors.initials: S
authors.lastname: Yamada
authors.affiliation: Department of Pathology and Cell Biology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
authors.forename: Aya
authors.initials: A
authors.lastname: Nawata
authors.affiliation: Department of Dermatology and Immunology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
authors.forename: Manabu
authors.initials: M
authors.lastname: Yoshioka
authors.affiliation: Department of Pathology, Field of Oncology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
authors.forename: Tsubasa
authors.initials: T
authors.lastname: Hiraki
authors.affiliation: Department of Pathology, Field of Oncology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
authors.forename: Michiyo
authors.initials: M
authors.lastname: Higashi
authors.affiliation: Department of Pathology, Field of Oncology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Hatanaka
authors.affiliation: Department of Pathology, Field of Oncology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
authors.forename: Akihide
authors.initials: A
authors.lastname: Tanimoto
mesh_terms: D000368:Aged; D003937:Diagnosis, Differential; D006801:Humans; D008198:Lymph Nodes / Q000473:pathology*; D008207:Lymphatic Metastasis; D008297:Male; D008545:Melanoma / Q000175:diagnosis* / Q000276:immunology / Q000473:pathology; D009365:Neoplasm Regression, Spontaneous; D018329:Nevus, Blue / Q000175:diagnosis* / Q000276:immunology / Q000473:pathology; D012878:Skin Neoplasms / Q000175:diagnosis* / Q000276:immunology / Q000473:pathology; D000096142:Cutaneous Malignant Melanoma