Dermatologica Sinica

: 2020  |  Volume : 38  |  Issue : 2  |  Page : 121--122

Primary thin nodular melanoma: An early tumorigenic vertical growth phase melanoma

Luca Roncati, Francesco Piscioli 
 Department of Medical and Surgical Sciences, University Hospital of Modena, Modena (MO), Italy

Correspondence Address:
Dr. Luca Roncati
Department of Medical and Surgical Sciences, Institute of Pathology, University Hospital of Modena, Policlinico, I-41124 Modena (MO)

How to cite this article:
Roncati L, Piscioli F. Primary thin nodular melanoma: An early tumorigenic vertical growth phase melanoma.Dermatol Sin 2020;38:121-122

How to cite this URL:
Roncati L, Piscioli F. Primary thin nodular melanoma: An early tumorigenic vertical growth phase melanoma. Dermatol Sin [serial online] 2020 [cited 2023 Feb 5 ];38:121-122
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Full Text

Dear Editor,

Nodular melanoma (NM) is the most fatal subtype of melanoma because it tends to grow more rapidly in-depth than on the skin surface.[1] Grossly, it is most often darkly pigmented; however, some NMs can be light brown, multicolored, or even colorless; an ulcerated and/or bleeding lesion is commonly encountered.[2] The microscopic hallmarks are dome-shaped dermal nodule with pushing borders, epidermal thinning, striking cytological atypia, high mitotic and proliferative index, lymphovascular invasion or perineural infiltration, and sometimes, tumor necrosis. According to the previous literature, NM can be considered “thin” when <1.3 mm in thickness.[3] Unlike superficial spreading melanoma (SSM), lentigo maligna melanoma, and acral lentiginous melanoma, NM is devoid of a radial growth phase (RGP) because it directly arises from transformed dermal melanocytes; therefore, it is characterized by the presence of a vertical growth phase (VGP) from the onset.[4] In a recent study, 20,132 melanomas (NM: 5062; SSM: 15,070), diagnosed in 17 centers in Europe, USA, and Australia between 2006 and 2015, have been reexamined by multivariate logistic regression analysis with emphasis in pT1 (≤1.0 mm) melanomas. Compared to pT1 SSM, pT1 NM has been found to be associated with a constellation of aggressive characteristics, such as higher mitotic rate and regional metastasis, that confer a worse prognosis.[5] Following a histogenetic view, RGP is considered a nontumorigenic growth phase limited to the epidermis (in situ) or to the papillary dermis (microinvasive), lacking of metastatic competence; on the contrary, VGP represents a tumorigenic growth phase, burdened by nodular confluence, deeper extension into the dermis or beyond, mitotic activity, and metastatic potential.[6],[7] VGP always follows RGP with the only exception of NM, as above referred. Today, the Breslow depth remains the most important prognostic factor for clinically localized primary melanomas, allowing to distinguish them in ultrathin (≤0.5 mm), thin (≤1 mm), thick (>1 mm), or ultrathick (>6 mm).[8] A histogenetic approach to the Breslow depth permits to explain the debated issue why thin NM behaves aggressively, because it possesses an early tumorigenic VGP inside it.[9] We believe that a renewed histogenetic approach to all melanoma subtypes of the International Classification of Diseases for Oncology, based on the growth phase distinction, deserves a wide scientific dissemination, for a better stratification and clinical management of the individual cases. In comparison with the 7th Edition, the 8th Edition of the American Joint Committee on Cancer (AJCC) staging system no longer considers mitotic count in a or b T1 categorization, but it adopts a substratification based on Breslow's depth and ulceration (pT1a <0.8 mm without ulceration; pT1b <0.8 mm with ulceration or 0.8–1.0 mm with or without ulceration).[10] Although the probability to encounter VGP increases with the depth of thin melanoma and this justifies the choice of a cutoff equal to 0.8 mm, the new AJCC staging system runs the risk to underestimate the metastatic competence of thin melanoma < 0.8 mm, in which a tumorigenic VGP may be found anyway.[10] In practice, the histogenetic approach would allow to identify those thin melanomas to be submitted to sentinel lymph node biopsy, because burdened by a tumorigenic VGP inside them, despite their thickness. The term “stratified medicine” has just been introduced to describe the concept of a modern medicine ad personam, focused on decisions, practices, and interventions tailored to the single patient, and based on the calculation of individual risk for disease progression. To meet these demands, thin NM should be considered a high-risk early tumorigenic VGP melanoma to be included in future prognostic stratifications.

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