Linear variant of large plaque-type blue naevus with subcutaneous cellular nodules

The clinico-pathological spectrum of plaque-type blue naevi and their potential for malignant transformation

AIMS

Plaque-type blue naevi are rare melanocytic tumours presenting as large, pigmented plaques at birth or during childhood. There is a risk for malignant transformation, but no larger comprehensive studies exist and the diagnosis is challenging, especially on limited biopsy material. The aim is to describe the clinicopathological features and behaviour of the disease more comprehensively.

METHODS AND RESULTS

We retrieved eight plaque-type blue naevi, presenting as large, pigmented plaques (median = 7 cm; range = 3-26) most frequently affecting the scalp (four) followed by the cheek, arm, abdominal wall and gluteal cleft (one each), with a slight female predilection. Median age at time of biopsy was 39.5 years (range = 15-90), but three tumours had been present at birth and one since childhood. Histopathologically, the tumours were poorly circumscribed and composed of cellular fascicles of uniform spindle cells in a background of variably prominent pigmented dendritic cells affecting dermis and subcutaneous tissues. The majority had mutations in GNAQ. One tumour showed malignant transformation, characterised by an expansile nodule of pleomorphic epithelioid melanocytes with rhabdoid morphology, high mitotic activity and areas of necrosis. This patient developed metastatic melanoma to lymph nodes. All patients are alive with a median follow-up of 60 months.

CONCLUSION

Plaque-type blue naevi are diagnostically challenging tumours with risk for malignant transformation. Awareness and familiarity with the salient clinicopathological features are necessary for reliable diagnosis, and long-term clinical follow-up is required to monitor for malignant transformation.

Unraveling the Mysteries of Perineural Invasion in Benign and Malignant Conditions

Perineural invasion (PNI) is defined as the dissemination of neoplastic cells within the perineural space. PNI can be a strong indicator of malignancy and is linked to poor prognosis and adverse outcomes in various malignant neoplasms; nevertheless, it can also be seen in benign pathologic conditions. In this review article, we discuss various signaling pathways and neurotrophic factors implicated in the development and progression of PNI. We also describe the methodology, benefits, and limitations of different in vitro, ex vivo, and in vivo models of PNI. The spectrum of presentation for PNI can range from diffuse spread within large nerves ("named" nerves) all the way through localized spread into unnamed microscopic nerves. Therefore, the clinical significance of PNI is related to its extent rather than its mere presence or absence. In this article, we discuss the guidelines for the identification and quantification of PNI in different malignant neoplasms based on the College of American Pathologists (CAP) and World Health Organization (WHO) recommendations. We also describe benign pathologic conditions and neoplasms demonstrating PNI and potential mimics of PNI. Finally, we explore avenues for the future development of targeted therapy options via modulation of signaling pathways involved in PNI.

A cellular blue nevus with pigmented epithelioid melanocytoma-like pattern on the ipsilateral upper arm associated with a congenital plaque-type blue nevus on the hand

A 36-year-old man presented with a subcutaneous nodule on the right upper arm. A small nodule had developed 8 years earlier, and grew in size, accompanied by a tingling sensation and numbness. In addition, he had a bluish irregular patch on the right hand since birth, which crossed from the palm to the dorsal hand. Skin biopsies from the hand showed a heavily pigmented melanocyte proliferation in the dermis with perieccrine, perivascular, and perineural involvement, and a diagnosis of congenital plaque-type blue nevus was made. The tumor on the arm was located closely along the median nerve, and was observed as a large black pedunculated round tumor. Histopathologically, the tumor on the arm consisted of densely packed tissue with nevoid cells without atypia in the larger nodular part, and heavily pigmented spindle and epithelioid melanocytes in the slender stalk area, which was diagnosed as cellular blue nevus with pigmented epithelioid melanocytoma-like pattern. Next-generation sequencing revealed GNAQ mutations in the hand lesion, and in the lesions on the arm. This case suggests that the areas of skin following the same neural distribution of a congenital plaque-type blue nevus on the extremities should be followed up for secondary changes.