Cyclin D1 demonstrates superior sensitivity and consistent nuclear expression compared with MiTF in cellular neurothekeoma.

Cellular neurothekeoma is an uncommon dermal neoplasm that frequently overlaps histologically with fibrohistiocytic and melanocytic tumors, particularly in superficial or limited biopsies. MiTF immunohistochemistry is commonly used for diagnostic support but shows inconsistent sensitivity with variable and often focal expression patterns, which can complicate interpretation. Cyclin D1 is a widely available nuclear marker expressed in some related fibrohistiocytic tumors, but its performance in cellular neurothekeoma has not been studied. Eleven cellular neurothekeomas diagnosed over a 7-year period were identified. Immunohistochemistry for cyclin D1 and MiTF was performed on formalin-fixed, paraffin-embedded tissue. Slides were independently scored using the blue-brown color H-score method, including assessment of overall H-scores and the proportion of tumor nuclei staining at ≥ 2+ intensity. Cyclin D1 showed consistently strong nuclear expression in all cases (11/11, 100%), with a median H-score of 205 (IQR 200-222.5), compared with 40 for MiTF (IQR 27.5-115) (p < 0.001). Strong (≥ 2+) nuclear staining was present in a median of 90% of tumor cells with cyclin D1 (IQR 82.5-100), versus 10% with microphthalmia transcription factor (IQR 0-35) (p < 0.001). MiTF was interpreted as positive in fewer than half of cases (5/11, 45%). Cyclin D1 demonstrated uniform, strong nuclear expression and superior sensitivity compared with MiTF, supporting its use as a sensitive and dependable immunohistochemical marker for cellular neurothekeoma.