Malignant Melanoma With Paradoxical Maturation

Abstract

Typically, melanocytic nevi "mature" (i.e., exhibit a morphologic shift to smaller or spindle cells with progressive depth in the dermis). In contrast, most malignant melanomas (conventional MMs) lack maturation, and are composed of large pleomorphic cells throughout. The authors describe a series of melanomas with paradoxical maturation mimicking the pattern of nevi. Seventeen primary invasive melanomas with paradoxical maturation (IMPs), two epidermotropic metastatic melanomas with maturation (EMMMs), 13 compound nevi (CN), and 14 conventional MMs without apparent maturation were analyzed by histologic, cytomorphometric, and immunohistochemical techniques. With increasing dermal depth, both CN and IMPs had smaller nuclear and cellular areas, and decreased expression of Ki-67, glycoprotein (gp)100 (with HMB-45), and tyrosinase. IMPs had significant differences from conventional MMs; namely, smaller nuclear and cytoplasmic areas (deep), and decreased expression of Ki-67 (superficial and deep), gp100 (deep), and tyrosinase (deep). IMPs also had notable differences from CN: namely, larger nuclear and cellular areas, more confluence, more mitotic figures, increased Ki-67 and gp100 expression in both the superficial and deep portions, and more melanin (deep). The two EMMMs exhibited histologic and immunohistochemical features similar to the primary IMPs. IMP, because of its mimicry of nevus, can present a diagnostic hazard. The authors propose histologic, morphometric, and immunohistochemical criteria that facilitate recognition and accurate diagnosis of this unusual variant of melanoma.

Atypical histologic and immunohistochemical findings in melanocytic nevi after liquid nitrogen cryotherapy

“…1,6 In contrast, most melanomas lack maturation but exhibit relatively uniform cytology in both superficial and deep components. They also demonstrate large, hyperchromatic nuclei with irregular nuclear membranes and prominent nucleoli.…”

“…They also demonstrate large, hyperchromatic nuclei with irregular nuclear membranes and prominent nucleoli. 1 The histologic findings of a large series of nonsurgically traumatized nevi have been previously described, but the kinds of trauma were not elucidated. 7 Trau et al 8 observed that recurrent lesions after laser therapy often have superficial similarities with melanoma, both clinically and histologically.…”

“…In contrast, most melanomas lack such maturation. 1 Junctional melanocytic nevi and the epidermal component of compound nevi usually exhibit reactivity for HMB-45. 2,3 The dermal component of common compound nevi and intradermal nevi are generally negative for HMB-45.…”

Fluorescence in situ hybridization as a tool for microstaging in malignant melanoma

“…In the latter, the deepest portion of the melanoma can show diminution in the size of nests and individual cells, thereby mimicking the pattern of a benign nevus. 8 We have shown earlier that a fluorescence in situ hybridization (FISH) assay targeting 6p25 (RREB1), 6q23 (MYB), 11q13 (CCND1) and CEP6 could distinguish benign and malignant melanocytic neoplasms with high sensitivity and specificity. 9 In this study, we evaluated 36 melanomas with associated nevi and 6 nevoid melanomas with deep dermal involvement using FISH with probes targeting 6p25, 6q23, CEP6 and 11q13.…”

Aberrant expression of HMB-45 in traumatized melanocytic nevi

“…Histologic maturation is described as a morphologic change of large and epithelioid type A nevomelanocytes to smaller and spindle-shaped type C nevomelanocytes with progressive descent into the dermis. 1,2 Conventional malignant melanomas display similar cytology in both their superficial and deep portions (this is not the case with melanomas that paradoxically do not exhibit such maturation; see below). 2 This lack of maturation provides a useful visual clue to the correct diagnosis of melanoma.…”