P75 nerve growth factor receptor as a useful marker to distinguish spindle cell melanoma from other spindle cell neoplasms of sun-damaged skin.

P75 nerve growth factor receptor (p75 NGF-R) is a low-affinity receptor expressed on the surface of neural crest-derived cells and in a variety of neural tumors. Strong p75 NGF-R expression has been found in spindle cell melanoma (SCM). We studied spindle cell neoplasms of sun-damaged skin to determine whether this marker can reliably distinguish between SCM and other spindle cell malignancies. We evaluated the staining of p75 NGF-R, S100, and HMB-45 in 11 cases of SCM, 16 cases of spindle cell squamous cell carcinoma (SCSCC), 19 cases of spindle cell atypical fibroxanthoma, 6 cases of cutaneous leiomyosarcoma, and 20 scars. Staining with p75 NGF-R was positive in all 11 of 11 (100%) cases of SCM, whereas S100 stained 10 of 11 (91%) cases, and HMB-45 was negative in all SCMs. In addition, there was superior intensity of the staining for p75 NGF-R in comparison to S100. P75-NGF-R showed focal positivity in 3 of 16 (19%) cases of SCSCC. None of the rest of the cases of SCSCC, and none of the cases of spindle cell atypical fibroxanthoma, cutaneous leiomyosarcoma, and scars expressed p75 NGF-R, S100, or HMB-45. P75 NGF-R is a useful marker to distinguish SCM from other spindle cell neoplasms of sun-damaged skin. This marker exhibits greater sensitivity than S100 in identifying SCM and may be a useful diagnostic and ancillary stain especially in the setting of an S100 negative spindle cell neoplasm.

P75 nerve growth factor receptor staining is superior to S100 in identifying spindle cell and desmoplastic melanoma.

BACKGROUND: Spindle cell melanoma (SCM) including desmoplastic melanoma (DM) is a rare variant of malignant melanoma that may present diagnostic difficulties particularly when staining with S100 is negative, weak, focal, or a combination of these. Conventional melanocytic markers in SCM are usually negative. OBJECTIVE: We sought to compare the staining of p75 nerve growth factor receptor (NGF-R) and S100 in SCMs. METHODS: We evaluated the staining of p75 NGF-R and S100 in 13 cases of SCMs: 3 SCMs without desmoplasia, 5 pure DMs, and 5 combined DMs with a conventional component. RESULTS: Staining with p75 NGF-R was positive in 13 of 13 (100%) cases of SCMs. In 3 cases the intensity of staining and the percentage of cells staining with this marker were greater than those with S100. One case of SCM was negative for S100 but demonstrated strong expression of p75 NGF-R. One case was focally and weakly positive with S100 but expressed strong positive staining with p75 NGF-R. Absence of staining with p75 NGF-R was noted in the conventional round cell component of two of 5 (40%) combined DMs whereas the same areas were strongly positive for human melanoma black (HMB)-45 and Melan-A. In 5 of 5 (100%) cases of combined DMs the desmoplastic component stained positive with p75 NGF-R, demonstrating an inverse relationship with the staining of conventional melanocytic markers. LIMITATIONS: Small study size was a limitation. CONCLUSION: p75 NGF-R exhibits superior staining characteristics and greater sensitivity in identifying SCM and DMs than S100. P75 NGF-R may be a useful diagnostic and ancillary stain in addition to S100.