Diagnosis | GIST (rectum/ prostate) | Leiomyoma (rectum/prostate) | Leiomyosarcoma (rectum/prostate) | Schwannoma (rectum/prostate) | Fibromatosis (mesenteric) | Solitary fibrous tumour (prostate) | Malignant melanoma (rectum/ prostate) |
---|---|---|---|---|---|---|---|
Growth Pattern | Fascicles, storiform or palisading | Fascicles | Fascicles | Antoni A/ Antoni B | Parallel fascicles, collagenous background | “Patternless pattern”, collagenous background, staghorn vessels | Diffuse / nested |
Cell Type | Spindle cell, high cellularity, no perinuclear vacuolization | Spindle cell, “cigar-shaped” nuclei, perinuclear vacuolization, low cellularity | Spindle cells, “cigar-shaped nuclei, atypia and intense nuclear pleomorphism, vacuolization, high cellularity | Spindle cells, wavy nuclei, nuclear atypia may be present | Bland spindle or strellate-cells, low to moderate cellularity | Spindle cells, low or high cellularity, pleomorphism (variable) | Epithelioid (rarely spindle cell) |
Mitosis | Few to many | Few | Frequent | Rare | Rare | 0-15 / 10 HPF | Frequent |
Necrosis/ Hemorrhage | May be present | Absent | Present | Sometimes present | Absent | Variable | Usually present |
CD 117 | Consistenly positive (cytoplasmic and membranous) | Negative | Negative | Negative | Positive sometimes (cytoplasmic) | Negative | Rarely positive |
CD34 | Consistenly positive | Rarely positive | Negative | Sometimes focal | Very rare | Positive | Negative |
Actina (SMA) | Sometimes positive | Positive | Positive | Negative | Positive | Rarely | Negative |
Desmina | Rarely | Positive | Positive | Negative | Very rare | Negative | Negative |
S-100 | Rarely | Very rare | Very rare | Strongly positive | Negative | Negative | Positive |
HMB-45 | Negative | Negative | Negative | Negative | Negative | Negative | Positive |
Beta-Catenin | Negative | Negative | Negative | Negative | Positive | Negative | Negative |