Clinicopathological study of blue nevi of the gastrointestinal (GI) tract: first case series

Melanoma arising in extracutaneous cellular blue nevus: report of two cases with comparison to cutaneous counterparts and uveal melanoma

AIMS

Blue nevi are benign melanocytic lesions that typically occur in the dermis. Melanoma arising in blue nevus is rare and shows a molecular profile distinct from conventional forms of cutaneous melanoma and more similar to uveal melanoma and central nervous system (CNS) melanocytomas. In contrast to conventional cutaneous melanoma, these tumor types typically show activating driver mutations in GNAQ or GNA11, a low mutational burden without evidence of a UV signature, and a reproducible pattern of chromosomal copy number changes. Blue nevi can also occur at extracutaneous sites. Here we report two cases of melanoma arising in extracutaneous blue nevus and compare their molecular features to cohorts of melanoma arising in cutaneous blue nevus (5 patients) and uveal melanoma (6 patients).

METHODS AND RESULTS

We describe the clinical, histomorphologic, immunohistochemical, and molecular findings in these two cases of melanoma arising in extracutaneous blue nevus. We compare their molecular profiles to melanomas arising in cutaneous blue nevus and uveal melanoma using a targeted next-generation DNA sequencing platform and find striking similarities between all three groups.

CONCLUSIONS

The close relationship between blue nevus-associated melanomas, regardless of their anatomic site, supports and validates the concept of melanoma arising in extracutaneous blue nevus and suggests that the two groups share common pathogenic mechanisms. The similarity of both groups to uveal melanoma in turn supports the close relationship between blue nevus-associated melanoma, uveal melanoma, and CNS melanocytoma, and their distinction from conventional UV-associated melanoma. These findings have important implications for prognosis and therapy.

Large Plaque-type Blue Nevus with GNAQ Q209P Mutation, Involving Mammary Gland Tissue: Under-Recognized Mammary Condition as an Origin of Primary Mammary Melanocytic Tumors

ABSTRACT

Plaque-type blue nevus is a rare variant of blue nevi that was first described in 1954. This article presents clinical, macroscopic, histopathological, and genetic findings for a case of large plaque-type blue nevus expanding into the mammary gland tissue as well as the skin of the right breast. A 63-year-old woman presented with a congenital, large, blue-colored macule limited to the hypochondriac area of the right breast. A nodule 8 mm in diameter was also present in the mammary gland tissue. Magnetic resonance imaging was unable to detect diffuse melanin deposition in the mammary gland tissue, but pigmentation in the whole mammary parenchyma was observed in the cut surfaces of the mastectomy specimen. Histopathology revealed a sparse distribution of dendritic melanocytes in whole sections of the mammary fibrous tissue and partial sections of the dermis. The histopathological criteria for atypical cellular blue nevus were fulfilled for the mammary tumor. Nodal blue nevus was diagnosed in the sentinel lymph node. Sanger sequencing confirmed the GNAQ Q209P mutation, which was also identified in all 4 literature cases of plaque-type blue nevus, but rarely in conventional blue nevi and uveal melanoma. It should be noted that plaque-type blue nevus can expand into the mammary gland tissue, even if the pigmented lesion does not exist on the overlying breast skin. The mammary condition can be the origin of primary mammary melanocytic tumors. Mosaicism of the GNAQ Q209P mutation can be a characteristic genetic alteration to extensive blue nevi, including plaque-type blue nevus.