Indeterminate cell histiocytosis with naïve cells

Area of Science:

• Dermatopathology
• Oncology
• Immunohistochemistry

Background:

• Histiocytoses encompass disorders of mononuclear-macrophage and dendritic cells, including Langerhans cell histiocytosis (LCH) and indeterminate cell histiocytosis (ICH).
• Indeterminate cell histiocytosis (ICH) is an exceptionally rare neoplastic dendritic cell disorder with poorly understood origins and pathogenesis.
• ICH is characterized by dendritic cell proliferation, immunophenotypically resembling Langerhans cells (CD1a+, S-100+) but lacking Birbeck granules.

Observation:

• A 24-year-old male presented with a reddish-brown chest wall nodule.
• Clinical, histopathological, immunohistochemical, and ultrastructural analyses confirmed features typical of ICH.
• The patient remained disease-free with no recurrence or metastasis after 24 months of follow-up.

Findings:

• Unusual histopathological findings included unidentified cells with Langerhans-like features that were negative for S-100, CD1a, Langerin, and CD68.
• The infiltrating cells demonstrated epidermotropism and, notably, neural and perineural invasion, features not previously reported in ICH.
• Absence of cellular atypia and mitosis was observed.

Implications:

• The unique features challenge current diagnostic paradigms for indeterminate cell histiocytosis.
• The findings support a potential reclassification or expanded definition of dendritic cell neoplasms.
• A tentative diagnosis of 'dendritic cell tumor, not otherwise specified' or 'Indeterminate cell histocytosis with naïve cells' is proposed for this case.