Pure and Mixed Desmoplastic Melanomas: A Retrospective Clinicopathologic Comparison of 33 Cases

Pure and Mixed Variants of Desmoplastic Melanoma: A Single-Center, Retrospective, Clinicopathologic Review

BACKGROUND

Desmoplastic melanoma (DM) is a rare melanoma variant. Prognostic indicators and survival vary widely and are further confounded by the histopathologic distinction between pure DM (pDM) and mixed DM (mDM) subtypes. The utility of current treatment guidelines is limited by the lack of evidence-based recommendations.

OBJECTIVE

To compare the clinicopathologic characteristics of pure and mixed subtypes of DMs.

METHODS

All cases of DM were identified from the Washington University in St Louis institutional pathology database between January 2000 and September 2022. Fifty-two cases were identified and subsequently categorized as pure ( n = 26) or mixed ( n = 26). Clinical and histopathologic data were collected and compared.

RESULTS

There were no differences in demographics or tumor location between pure and mixed subtypes. Patients with mDM were more likely to have mitoses present ( p = .03). There were no differences in Breslow depth, tumor diameter, level of invasion, ulceration, and lymphovascular or perineural invasion. The utilization of sentinel lymph node biopsy ( p = .17) and sentinel lymph node positivity ( p = .67) were also similar.

CONCLUSION

Despite histopathologic distinction between pDM and mDM, these subtypes were found to have similar clinicopathologic characteristics, including similar rates of sentinel lymph node metastasis.

Top 10 Differential Diagnoses for Desmoplastic Melanoma

BACKGROUND

Desmoplastic melanoma is a rare subtype of melanoma mainly appearing on sun-exposed skin. Clinically, it is many times non-pigmented and therefore the diagnosis is often not suspected.

METHODS

Review article.

RESULTS

In this paper we review the main histopathological, immunohistochemical, and molecular features of desmoplastic melanoma, as well as the top 10 morphologic differential diagnoses which should be considered in most cases. The histopathological pattern can be many times deceptive, mimicking a scar, a fibrous reaction, a fibrohistiocytic tumor such as a dermatofibroma, a vascular tumor such as angiosarcoma, a smooth muscle tumor such as leiomyosarcoma, or a neural tumor. Although an overlying atypical junctional melanocytic proliferation may be seen in most cases, it is absent in a significant percentage (up to 30%) of cases, making the diagnosis even more difficult in those instances. The range of diagnostic pitfalls is wide, which may present disastrous prognostic consequences.

CONCLUSION

Desmoplastic melanoma is often a difficult diagnosis to make, as it frequently shows nonspecific clinical findings and overlapping histologic features with many other tumors. However, the potential clinical and prognostic consequences of misdiagnosis as another entity are great. Therefore, this diagnosis must always be kept in mind when encountering spindle cell tumors affecting the head and neck area.