Primary dermal melanoma: clinical behaviour, prognosis and treatment

Primary dermal melanoma

Primary dermal melanoma (PDM) is a rare subtype of melanoma with an estimated incidence of <1%. PDM manifests entirely in the dermis or subcutis and histopathologically mimics cutaneous melanoma metastasis due to its lack of connection to the overlying epidermis. A thorough history and examination, including imaging evaluation for metastatic disease, reveals no prior history or concurrent primary cutaneous or metastatic melanoma lesion. Despite its histopathologic similarities to melanoma metastasis, PDM is associated with an unexpectedly favorable prognosis. This review discusses the clinical and histopathologic features of PDM as a distinct subtype of melanoma, as well as the current approach to clinical staging and management.

Metastatic melanoma and rare melanoma variants: a review

The histopathological diagnosis of melanoma is fraught with potential pitfalls. In the setting of cutaneous metastatic melanoma, it is important to recognise the various histological patterns that can be encountered from the more common to the rare, including epidermotropic, folliculotropic, naevoid, and blue naevus-like. In addition, melanoma is notorious for phenotypic plasticity. Thus, there are many different subtypes and cytomorphological variations that can be difficult to recognise as melanoma, particularly in the recurrent or metastatic setting. Select melanoma variants including primary dermal, clear cell, plasmacytoid, signet ring cell, small cell, myxoid, rhabdoid, and dedifferentiated melanoma will be discussed, in addition to composite melanocytic neoplasms. This review is intended to remind the practitioner of key concepts of metastatic disease and select rare melanoma variants, while providing practical guidelines for accurate diagnosis.

Primary Dermal Melanoma: A Case Report

ABSTRACT

Primary dermal melanoma (PDM) is defined as a primary melanoma tumor confined to the dermis, subcutis, or both, without epidermal involvement. The significant overlap of histopathological features in PDM and cutaneous metastatic melanoma makes diagnostic accuracy of PDM challenging. We present a case of a 48-year-old man with a nontender 1.5 × 1.5 cm subcutaneous nodule on the left leg, which had been present for years. Biopsy revealed a dermal tumor with melanocytic differentiation noted to be positive for SOX-10. Additional pathology findings included a high Ki-67 proliferation index and a loss of p16 expression. Pathology reports were consistent with primary tumor stage 4a, and the patient was referred to surgical oncology where examination and workup demonstrated no evidence of the residual lesion representing a metastasis from a primary site. As PDM is histologically indistinguishable from melanoma metastasis to the skin, clues including a history of an evolving subepidermal nodule and exclusion of previous or concurrent melanomas can assist in its accurate diagnosis. Currently, a consensus on the criteria, staging, and management of PDM does not exist. Poorly defined diagnostic criteria and general lack of awareness of PDM result in high rates of incorrect and late-stage diagnoses. This case report highlights the importance of physician familiarity with PDM to ensure accurate recognition, evidence-based management, and improved patient outcomes.

Case report of a primary subcutaneous melanoma; a surprising entity for a subcutaneous nodule

INTRODUCTION

A melanoma can originate at the subcutis without any visible skin lesion.

CASE PRESENTATION

A 73-year old patient came to the outpatient clinic with a subcutaneous nodule on the right thigh without any visible lesion of the skin. It turned out to be a primary subcutaneous melanoma that could be classified as a primary dermal melanoma (PDM).

DISCUSSION

A PDM is a very rare subtype of melanoma that stands out for its excellent prognosis in comparison to cutaneous melanomas. No valid reliable staging system or treatment guideline exists for this entity, Breslow depth might overestimate the clinical aggressiveness possibly leading to overtreatment.

CONCLUSION

It is of great importance for the clinician to be familiar with a primary dermal melanoma. It deserves an appropriate place in the current AJCC system and a treatment guideline for this unique melanoma subtype with relativity excellent prognosis would be beneficial.

Uncommon Subtypes of Malignant Melanomas: A Review Based on Clinical and Molecular Perspectives

Malignant melanoma represents the most aggressive type of skin cancer. Modern therapies, including targeted agents and immune checkpoint inhibitors, have changed the dismal prognosis that characterized this disease. However, most evidence was obtained by studying patients with frequent subtypes of cutaneous melanoma (CM). Consequently, there is an emerging need to understand the molecular basis and treatment approaches for unusual melanoma subtypes. Even a standardized definition of infrequent or rare melanoma is not clearly established. For that reason, we reviewed this challenging topic considering clinical and molecular perspectives, including uncommon CMs-not associated with classical V600E/K BRAF mutations-malignant mucosal and uveal melanomas, and some unusual independent entities, such as amelanotic, desmoplastic, or spitzoid melanomas. Finally, we collected information regarding melanomas from non-traditional primary sites, which emerge from locations as unique as meninges, dermis, lymph nodes, the esophagus, and breasts. The aim of this review is to summarize and highlight the main scientific evidence regarding rare melanomas, with a particular focus on treatment perspectives.