Spindle Cell Melanoma and Interdigitating Dendritic Cell Sarcoma

Abstract

Intranodal spindle cell lesions on biopsy are problematic for a surgical pathologist, often requiring an extensive immunohistochemical evaluation with variable and frequently unsatisfactory results. In the absence of a history of malignancy, the differential diagnosis of a spindle cell tumor must include both a primary nodal proliferation and a metastatic process. Particularly challenging are those lesions that share morphologic and immunohistochemical features; spindle cell melanomas (SCM) and interdigitating dendritic cell sarcomas (IDCS) belong to this category. At present, electron microscopy is the only method proposed to distinguish between the 2 entities; however, this method is often unavailable and impractical. In this study, we assessed the comparative immunophenotypes of 18 cases of SCM and 8 cases of IDCS, with particular emphasis on the expression of MUM-1, β-catenin, SOX-10, MiTF, and p75. Our results showed nearly equivalent staining patterns and profiles; 12% and 17% of IDCS and SCM were labeled for MUM-1, 75% and 83% stained for β-catenin, 0% and 24% expressed MiTF, and 100% and 94% labeled for p75, respectively. All cases of IDCS and SCM displayed strong nuclear reactivity for SOX-10. On the basis of our study and pertinent literature, the morphologic and immmunophenotypic features of SCM and IDCS appear to be virtually indistinguishable from one another, raising the question as to whether these 2 entities represent a pathobiologically similar or even identical process.

SOX‐10 staining in dermal scars

“…SOX‐10 is a reliable marker in evaluating sentinel lymph nodes for metastatic melanoma and identifying rare tumor cells in heavily regressed areas of metastatic melanoma with abundant melanophages . Immunohistochemical evaluation with SOX‐10 also has found utility in evaluation of intranodal spindle cell tumors …”

Spindle cell melanoma: Incidence and survival, 1973‑2017

“…Immunohistochemistry is a helpful tool in distinguishing SCM from other sarcomas and carcinomas ( 9 , 10 ). However, diagnosis remains a challenge as a number of sarcomas share some morphological and immunohistochemical features with SCM ( 5 , 11 ). Differentiation of SCM from desmoplastic melanoma is difficult because both melanomas are characterized by atypical, spindled, malignant melanocytes.…”

“…A limited number of case reports and incomplete retrospective case studies of the differential diagnostic viewpoints of SCM exist ( 3 , 4 , 11 – 15 ). To the best of our knowledge, few studies have reported SCM incidence, clinicopathologic features, treatment, treatment outcome and disease-specific independent prognostic factors.…”

Histiocytic and Dendritic Cell Sarcomas of Hematopoietic Origin Share Targetable Genomic Alterations Distinct from Follicular Dendritic Cell Sarcoma

“…Mutations in the MAPK pathway, as reported in case reports, were identified in a subset of tumors herein [ 48 , 49 , 50 , 51 , 52 , 53 , 54 ]. Our findings also highlight the diagnostic challenge of IDCS and its distinction from spindle‐cell melanoma, given their histologic and immunophenotypic overlap [ 55 ]. In difficult cases, analysis of mutation signature by NGS may be helpful in distinguishing metastatic melanoma from IDCS.…”