Cutaneous melanoma in situ: a review

Cutaneous melanoma in situ (MIS), also known as 'stage 0 melanoma', is a collection of malignant melanocytes in the epidermis and epithelial adnexa, without evidence of microinvasion to the papillary dermis. Distinct histological subtypes include lentigo maligna (LM), superficial spreading (SS) MIS and acral lentiginous (AL) MIS. LM is the most common subtype, usually diagnosed later in life (median age at diagnosis of 66-72 years) and associated with cumulative ultraviolet radiation exposure. SS MIS is associated with intense episodes of sun exposure and is more common on the trunk and extremities. AL MIS is seen in nonhair-bearing skin. AL MIS, although rare (0.6% of MIS in England), is found in a higher proportion in more pigmented skin types compared with other MIS subtypes. Most international studies between 1990 and 2019 report rising incidence for MIS. US data show a decline in the incidence of LM between 2015 and 2019. For 2013-2019 in England, the recorded incidence of LM is plateauing, whereas that of other MIS is rising. Definitive diagnosis of MIS is by histological examination of biopsied skin with immunohistochemistry but can be supported with dermoscopy and reflectance confocal microscopy. Surgical treatment (excision or Mohs micrographic surgery) is the gold standard. Depending on MIS subtype, other options such as cryotherapy, topical imiquimod, radiotherapy or watchful waiting may be appropriate. The latest 5-year net-survival rates in England between 2013 and 2015 are 98.6% for AL MIS and exceed 100% for all other MIS. This review summarizes the aetiology, pathogenesis, epidemiology, diagnosis and management of MIS.