Collagen triple helix repeat containing-1 in the differential diagnosis of dermatofibrosarcoma protuberans and dermatofibroma.

BACKGROUND: The distinction between dermatofibroma (DF) and dermatofibrosarcoma protuberans (DFSP) is a well-known challenge for dermatopathologists. Immunohistochemical stains have been used to augment routine histological examination to aid in differentiating DF from DFSP. Collagen triple helix repeat containing-1 (Cthrc1) was identified as a novel gene expressed in the adventitia and neointima on arterial injury. It is indicated to be a cell type-specific inhibitor of transforming growth factor-β, which in turn impacts collagen type I and III deposition, neointimal formation, and dedifferentiation of stem cells. Cthrc1 has also been shown to be highly active and potent in degrading extracellular matrix proteins and was found to be overexpressed in several malignant tumours, such as breast cancer and malignant melanoma. To our knowledge, however, expression of Cthrc1 in DFSP and DF has not been studied before.

OBJECTIVES: To assess the expression of Cthrc1 in DFSP and DF and to ascertain whether Cthrc1 is superior to antibodies traditionally used in differentiating DF from DFSP.

METHODS: Immunohistochemical staining was performed on 23 cases of DFSP and 35 cases of DF, using antibodies to Cthrc1, CD34, factor XIIIa, CD10 and stromelysin-3 (ST3).

RESULTS: Twenty-two of 23 (96%) DFSP samples were positive for Cthrc1, whereas 32 of 35 (91%) DF samples were negative. CD34 was expressed in most DFSPs (22 of 23, 96%), whereas it was completely negative in most cases of DF (29 of 35, 83%). Expression of factor XIIIa was found in most cases of DF (33 of 35, 94%), whereas it was completely absent in 21 of 23 (91%) DFSP cases. Expression of CD10 was found in most cases of DF (30 of 35, 86%), whereas it was completely absent in 13 of 23 (57%) DFSP cases. ST3 was expressed strongly in most cases of DF (32 of 35, 91%), whereas it was completely absent in 18 of 23 (78%) DFSP cases. The preferential Cthrc1 staining of DFSP in comparison with DF was statistically significant (P < 0·01).

CONCLUSIONS: We confirmed that Cthrc1 is a positive marker for DFSP and that Cthrc1 staining might be more reliable than markers traditionally used. Cthrc1 was not positive in absolutely [corrected] all cases of DFSP, and combination with CD34, factor XIIIa and ST3 immunostaining could make the distinction more reliable.