PRAME expression in fibrosarcomatous dermatofibrosarcoma protuberans

Abstract

PRAME (PReferentially expressed Antigen in MElanoma) was first identified as a malignant melanoma-specific antigen. Recently, a few cases of fibrosarcomatous dermatofibrosarcoma protuberans (FS-DFSP) were shown to have positivity for PRAME, while conventional dermatofibrosarcoma protuberans (C-DFSP) was negative. Because PRAME may be of diagnostic utility in FS-DFSP and is raising expectations as a new immunotherapy target, we examined the positivity of PRAME in FS-DFSP. Twenty-one cases of FS-DFSP and age/sex/location-matched cases of C-DFSP as a control group were examined by immunohistochemistry for CD34 and PRAME. The results were then evaluated by H-score, which was objectively and semi-quantitatively calculated using the open-source bioimaging analysis software QuPath. The results revealed that the PRAME H-score in FS-DFSP was significantly higher than that in C-DFSP (p = 0.0137). As for CD34, the H-score in FS-DFSP was significantly lower than that in C-DFSP (p < 0.001). Using these two immunohistochemical analyses in combination, the sensitivity and specificity for the diagnosis of FS-DFSP were 86% and 90%, respectively. Double staining of CD34 and PRAME revealed that PRAME-positive and CD34-positive areas did not overlap. This is the largest study to examine PRAME expression in FS-DFSP, and it confirmed the usefulness of PRAME in diagnosing this condition.

Keywords: Bioimaging analysis; CD34; Fibrosarcomatous dermatofibrosarcoma protuberans; PRAME; QuPath.

Fig. 1

Immunohistochemistry for PRAME in FS-DFSP and C-DFSP. A–C: FS-DFSP. A: Loupe image. The tumor is diffusely positive for PRAME. B: Magnified image (×400). The tumor cells are positively stained in the nucleus. C: QuPATH processed image of B shows the staining intensity (blue: negative, yellow: weakly positive, orange: moderately positive, red: strongly positive). D–F: C-DFSP. D: Loupe image. The tumor is negative for PRAME. E: Magnified image (×400). The tumor cells are negative for PRAME. F: QuPATH processed image of E shows the staining intensity (blue: negative).

Fig. 2

H-score (CD34) and mH-score (PRAME) differ significantly between FS-DFSP and C-DFSP. C-DFSP shows a higher CD34 H-score and a lower PRAME mH-score, while FS-DFSP shows the opposite pattern.

Fig. 3

Immunohistochemistry for CD34 in FS-DFSP and C-DFSP. A–C: FS-DFSP. A: Loupe image. The tumor cells are diffusely very weakly positive for CD34. B: Magnified image (×400). The tumor cells are mostly negative for CD34. C: QuPATH processed image of B shows the staining intensity (blue: negative, yellow: weakly positive, orange: moderately positive, red: strongly positive). D–F: C-DFSP. D: Loupe image. The tumor is diffusely positive for CD34. E: Magnified image (×400). The cytoplasmic membrane is diffusely positive for CD34. F: QuPATH processed image of E shows the staining intensity (blue: negative, yellow: weakly positive, orange: moderately positive, red: strongly positive).

Fig. 4

ROC curves of H-score (CD34), mH-score (PRAME), and H-score (CD34 − PRAME). H-score (CD34 − PRAME) shows the largest AUC.

Fig. 5

Two cases of double staining for CD34 (blue) and PRAME (brown). A, B: Case (1) C, D: Case (2) A, C: Loupe images. The PRAME-positive areas did not overlap the CD34-positive areas. B, D: Magnified images (×400). The PRAME-positive area shows decreased CD34 positivity.